Chemical composition of Mesopelagic fishes from the Eastern Gulf of Mexico

Citation
Chemical composition of Mesopelagic fishes from the Eastern Gulf of Mexico

Material Information

Title:
Chemical composition of Mesopelagic fishes from the Eastern Gulf of Mexico
Creator:
Stickney, Donna G.
Place of Publication:
Tampa, Florida
Publisher:
University of South Florida
Publication Date:
Language:
English
Physical Description:
x, 48 leaves : ill. ; 29 cm.

Subjects

Subjects / Keywords:
Marine fishes -- composition -- Mexico, Gulf of ( lcsh )
Dissertation, Academic -- Marine science -- Masters -- USF ( FTS )

Notes

General Note:
Thesis (M.S.)--University of South Florida, 1987. Bibliography: leaves 45-48.

Record Information

Source Institution:
University of South Florida
Holding Location:
Universtity of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
021364765 ( ALEPH )
18695593 ( OCLC )
F51-00022 ( USFLDC DOI )
f51.22 ( USFLDC Handle )

Postcard Information

Format:
Book

Downloads

This item is only available as the following downloads:


Full Text

PAGE 1

Graduate Council University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL MASTER'S THESIS This is to certify that the Master's Thesis of Donna Gandara Stickney with a major in Marine Science has been approved by the Examining Committee on November 10, 1987, as satisfactory for the Thesis requirement for the Master of Science degree. Thesis Committee: Major Proressor: J. J. Torres Member: T. L. Hopkins Member: E. S. Van Vleet Member: T. G. Bailey

PAGE 2

@Donna Stickney All Rights Reserved

PAGE 3

CHEMICAL COMPOSITION OF MESOPELAGIC FISHES FROM THE EASTERN GULF OF MEXICO by Donna G. stickney A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Marine Science in the University of South Florida December, 1987 Major Professor: Joseph J. Torres, Ph.D.

PAGE 4

ACKNOWLEDGEMENTS As with many endeavors, this thesis project was completed with the help of several people. Among those who made significant contributions is Dr. Jose Torres. I express sincere gratitude not only for his scientific and editorial comments, but his patience in working with me under strict time constraints. I would like to thank my other committee members, Dr. Tom Hopkins, Dr. Ted Van Vleet and Dr. Tom Bailey for helpful suggestions, providing valuable literature references and for their time involved with this project. Thanks to Jack Gartner for being my mentor both at sea and during preparation of the written thesis. His assistance in providing scientific expertise on mesopelagic fishes is greatly appreciated. On a personal note, thanks Jack and Linda Bingler for a chance to relax at my "going away" party. The chicken was superbly prepared however, the myctophid cake, a culinary masterpiece was the creme de la creme. Appreciation is expressed to Gregg Tolley for reviewing my thesis, computer assistance, helpful discussions regarding my project, and for being a good friend. Thanks to Tom Lancraft for providing expertise on midwater fishes, letting me deplete his library of references, and for helpful presentation comments. Several ii

PAGE 5

other people were of invaluable assistance. Thanks to Mike Mitchell for always providing immediate computer assistance, to Tony Greco, an excellent office mate, for being so thoughtful during times when I was so busy,-to Joe Donnelly, for comradery, helpful comments regarding my thesis, and teaching me to play volleyball, and to Mary DeFlaun for helpful presentation comments, for zeroxing figures when I was rushed and for being there as a friend. Gratitude is expressed to Ernest Peebles for discussions on statistics and for listening to my presentation, to Dave Williams for repeating my slides even though he had other work to do and for trying to provide time for me to shop, to Steve Snyder, Sue Davis, and Marie Azzarello for many late night discussions, cups of coffee, graphics materials and general student comradery. Thanks to Wade Jefferies for letting me borrow his thesis as a model even though his copyright page is in the wrong order, to Jeff Brown for always being helpful and for remembering to turn on the projector, and to Jennifer McNellie for coming to my aid by assisting with pagination when time was crucial, for showing me the way by defending before me, and for years of valuable friendship. A special thanks to Ivanhoe and Roweena for putting up with late night dinners and always being happy to see me. Most importantly, thanks to my husband, Randy for making me be tough enough to complete this project at the same time that so many other things had to be accomplised, and for his love and patience over several years. iii

PAGE 6

TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ABSTRACT INTRODUCTION MATERIALS AND METHODS Collection of specimens Proximate Analysis Ash-free dry weight, total ash and skeletal ash Lipid Protein Carbohydrate Carbon, Hydrogen and Nitrogen Caloric Content Vertical distributions swimbladders Data Statistics RESULTS Water content Ash-free dry weight, total ash weight, and skeletal ash iv vi vii viii 1 4 4 5 6 6 6 7 7 8 8 9 13 13 15 15 15

PAGE 7

Lipid 18 Protein 22 Carbohydrate 22 Caloric content 24 Carbon 24 Hydrogen 26 Nitrogen 26 DISCUSSION 28 CONCLUSIONS 43 LITERATURE CITED 45 v

PAGE 8

LIST OF TABLES 1. List of family, genus and species, symbol (SYM), 10 migration, depth ranges, minimum depth of occurrence (MOO), standard length (SL), wet weight (WW), water, ash-free dry weight (AFDW), and skeletal ash (SA). 2. List of family, genus and species, lipid content 19 (%AFDW and %WW), protein content (%AFDW and %WW) carbohydrate content (%AFDW and %WW), hydrogen (%AFDW), nitro2In (%AFDW), and caloric content (Kcal 100 g ww ). 3. Comparison of chemical composition with data from 34 other investigators on congeneric fishes. vi

PAGE 9

1. 2 0 3 0 4. 5. 6. 7. LIST OF FIGURES Regression of water content (% wet weight) on 16 minimum depth of occurrence (MOO) in 21 species of midwater fishes from the Gulf of Mexico. Regression of ash-free dry weight (% dry weight) on 17 minimum depth of occurrence (MOO) in 21 species of midwater fishes from the Gulf of Mexico. Regression of protein content % wet weight) on 23 minimum depth of occurrence (MOO) in 21 species of midwater fishes from the Gulf of Mexico. Regression of caloric content (Kcal 100 g WW 1 ) on 25 minimum depth of occurrence (MOO) in 21 species of midwater fishes from the Gulf of Mexico. Regression of protein content (%AFDW) on nitrogen 27 content (%AFDW) in 20 species of midwater fishes from the Gulf of Mexico. Comparison of 5 regression curves of lipid content 35 (% wet weight) on minimum depth of occurrence (MOO) in midwater fishes. Comparison of 4 regression curves of caloric content 41 (Kcal 100 g ww-1 ) on minimum depth of occurrence in midwater fishes. vii

PAGE 10

CHEMICAL COMPOSITION OF MESOPELAGIC FISHES FROM THE EASTERN GULF OF MEXICO by Donna G. Stickney An Abstract Of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Marine Science in The University of South Florida December, 1987 Major Professor: Joseph J. Torres viii

PAGE 11

The chemical compositions of 33 species of mesopelagic fishes from the eastern Gulf of Mexico were determined. Water content, ash-free dry weight (%dry weight), and protein content (% wet weight) decreased with increasing minimum depth of occurrence. Lipid content, expressed as % wet weight or % ash-free dry weight, did not decrease with minimum depth of occurrence. Skeletal ash (% wet weight) showed a general decrease with minimum depth of occurrence, whereas carbohydrate demonstrated no trend with depth. Eastern Gulf of Mexico fishes exhibit variable water content, low lipid and high protein content resulting in a relatively low caloric content. These results are generally consistent with trends in fishes from stable regions of low productivity, such as those observed for the eastern North Pacific gyre. The constant food supply provided by a stable environment may obviate the need for large lipid reserves in contrast to colder waters where food availability is seasonally determined. In addition, the large energy requirements from diel excursions into high temperature surface waters by the many vertically migrating fishes of this region, may influence lipid deposition. The relatively high protein content found in migrators compared to that of non-migrators or weak migrators indicates locomotory demands influence the percentage of protein found ix

PAGE 12

in Gulf fishes. The lack of a positive correlation between protein content and the food availability of a zoogeographic region, suggested in previous studies, is supported here. Abstract approved: Major Professor Associate Professor of oceanography Date of Approval X

PAGE 13

INTRODUCTION The major biochemical components of mesopelagic fishes are water, lipid, protein, ash and carbohydrate (Childress, 1977). Water content tends to increase with increasing depth while lipid, protein, skeletal ash and caloric content decrease (Childress and Nygaard, 1973; Bailey and Robison, 1986) Carbohydrates are generally low in midwater fishes and do not show trends with depth (Childress and Nygaard, 1973). In deeper living species, dilute fluids are substituted for organic matter (Childress and Nygaard, 1973). This enhances the conservation of metabolic energy and achievement of near neutral buoyancy. Discouragement of predation and a more energy efficient prey capture is made possible through increased size related to a reduction in caloric content per unit weight required as energy for growth. (Childress and Nygaard, 1973). The two predominant organic components of mesopelagic fishes are lipid and protein. Lipids serve as an energy store and correlate with food availability, independent of depth related factors (Bailey and Robison, 1986). The decline in protein content with depth is consistent with the reduction of muscle mass (Blaxter et al., 1971), metabolic

PAGE 14

rate (Childress and Nygaard, 1973; Childress et al., 1980), and tissue density observed in deeper living species (Childress and Nygaard, 1974; Childress et al., 1980). 2 Species proximate composition also varies between regions. In midwater fish inhabiting the highly productive, cold waters of the California current, water content increased while all other components decreased with depth (Childress and Nygaard, 1973). Higher water and protein content were found in mesopelagic fishes from the warmer, low productivity waters of the eastern North Pacific gyre than in species from the California Current or the transition region between the Current and gyre (Bailey and Robison, 1986). In a polar region, such as the Antarctic, total lipid values for many oganisms were reported as similar to temperate species (Reinhardt, and Van Vleet, 1986). In general, regions of high productivity typically have increased lipid and caloric content, whereas regions of low productivity are distinguished by high protein and low lipids (Childress and Nygaard, 1973; Bailey and Robison, 198 6) Similar to the eastern North Pacific gyre, the eastern Gulf of Mexico is a stable, warm water region of low productivity, although it has many vertically migrating midwater fishes. The proximate composition of Gulf species would be expected to reflect the environmental influences of high temperatures, which may result in higher energy expenditures, and the low, although constant food supply.

PAGE 15

This study examines the chemical composition of midwater fishes from the eastern Gulf of Mexico. The results are discussed with respect to physical and biological characteristics which affect proximate composition and make this region different from those previously examined. 3

PAGE 16

4 MATERIALS AND METHODS Collection of specimens Specimens were collected on several cruises in the eastern central Gulf of Mexico within a ten nautical mile radius of 27N, 86w. Cruises were during May-June 1984, July 1985, November 1985, and January 1986 aboard the R.V. Suncoaster. Individuals were taken in the upper 1000 m of the water column using a mouth-closing Tucker trawl with either a 3.2 m 2 or 6.5 m 2 mouth area. The body of the trawl was constructed of 1.1 em stretch mesh with a 1.1 em stretch mesh conical fish catcher fitted anterior to the 505 mesh codend (Hopkins et al., 1973; Hopkins and Baird, 1975). Towing speed was approximately 2 knots. Following net retrieval, fishes were selected for analysis, identified to species, measured to the nearest millimeter standard length (mm SL), blotted to remove excess moisture, and individually placed in polypropylene vials. samples were kept frozen at -2o0c at the lab until analyzed.

PAGE 17

5 Proximate Analyses Individual specimens were allowed to partially thaw, were remeasured to the nearest 0.1 mm SL, transferred to preweighed glass serum vials of appropriate sizes, and weighed to the nearest 0.01 g on a Mettler analytical balance. Any water inside the vials was considered to be part of the wet weight (WW) since all animals were blotted before freezing. After wet weights were obtained, specimens were once again frozen until hard, and then lyophilized in a Labconco freeze dryer. Lyophilization took place for a minimum of eight hours or until a constant weight was obtained. Specimens were then reweighed for dry weight (DW) determination in the same vial, and water content calculated from the difference between WW and DW determinations. Lyophilized specimens were stored in a vacuum dessicator over silica gel. They were reweighed for exact DW in preparation for slurry volume determination. Lyophilization was empirically determined to be a better method for drying than a 60 c oven because it is a more rapid process and results in a more easily homogenized sample. Each fish was homogenized in a Brinkmann Polytron homogenizer using enough deionized water to make a 25 mgjml slurry. The slurry was transferred to a glass tissue grinder for final homogenization. Individual aliquots were dispensed from the slurry for the various analyses.

PAGE 18

6 Ash-free dry weight, total ash and skeletal ash Two aliquots of 0.4 ml (10 mg DW) were dispensed into individual, preweighed aluminum pans and dried for 24 hours, at 60 c, to a constant weight. Dried samples were weighed and ashed in a 1000 Series International Plasma Corporation low temperature (110-150C) asher. Samples were reweighed to determine ash content and ash-free weight. Skeletal ash was estimated by assuming the solute concentration of the body fluids to be 40% that of sea water and subtracting the estimated solute ash from total ash to obtain the skeletal ash (Childress, 1973). Lipid Lipids were extracted from two aliquots (0.2 ml, 5.0 mg ow each) of homogenate using 2:1 methanol-chloroform according to the method of Bligh and Dyer (1959). Extracts were evaporated under a flow of N 2 at 30C and analyzed for lipid using the charring method of Marsh and Weinstein (1966), with stearic acid (Kodak) as the standard. Protein Aliquots of homogenate (0.1 ml; 2.5 mg DW) were diluted 1:10 into deionized water, mixed, and 0.1 ml dispensed into 3 test tubes each for protein analysis. Aliquots were

PAGE 19

7 increased to 0.2 ml volume using deionized water, with the standard (Sigma; human albumin and globulin) treated in an identical manner. A modification of the Lowry et al. method (1951) was used for protein determination. Carbohydrate Two aliquots of 0.4 ml each (10 mg DW) were dispensed into preweighed 5 ml centrifuge tubes and dried in a 60C oven to constant weight. The samples were then washed with acetone and ethyl ether to remove lipids and dried in a 60C oven. Trichloroacetic acid (10%) was added and samples were heated at 100C for 20 min to allow hydrolysis. The supernatant was removed and analyzed for carbohydrate using the method of Dubois et al. (1956), with D-glucose (Sigma) as the standard. Carbon, Hydrogen and Nitrogen Aliquots containing a minimum of 0.4 ml were transferred to glass vials with Teflon lined caps for carbon, hydrogen, and nitrogen analyses. Samples were dried in a Go0c oven, and immediately stored in an evacuated dessicator over silica gel until analyzed. CHN analysis was performed by combustion of the samples and detection of the combustion products in an automated CHN-analyzer (University of California at Santa Barbara, Control Equipment

PAGE 20

8 Corporation, Model 240 XE; equivalent to a Perkin Elmer eRN analyzer). Caloric content Absolute caloric values were calculated using the conversion factors of Brett and Groves (1979): 5.7 Kcal g-1 protein; 8.7 Kcal g-1 lipid; and 4.1 Kcal g-1, carbohydrate. The values provide an estimate of the caloric potential as food for predators of the different species examined. Vertical distributions Of the thirty-three species examined, there were twenty-four migrators, two weak migrators, and six non-migrators (migration/non-migration could not be determined for Maurolicus muelleri). Depth ranges for the fishes were obtained from Hopkins and Baird (1985) for Sternoptychidae, Gartner et al. (1987) for Myctophidae, Keene et al. (1987) for Poromitra and scopeloberyx and from the extensive data base generated by the USF midwater ecology group for Anoplogasteridae, Bathylagidae and Gonostomatidae. Vertical migration patterns and depth distributions reported were for species size ranges given, with the exception of some non-migratory individuals included in the size ranges of the family Myctophidae. Data were examined using the

PAGE 21

minimum depth of occurrence (MOO), "that depth below which 90% of the population lives" (Childress and Nygaard, 1973). In this study, MOO specifically refers to the shallowest depth at which any post-metamorphic member of a species has been found. 9 Assignment of migration categories correlated specific patterns of migration with MOO. Fishes were grouped into three categories based upon vertical migration patterns. The qsthree categories were: 1) migrators, which were defined as those species whose peak abundances were shifted by 200 meters during a diel cycle, 2) weak migrators, defined as species whose peak abundances were shifted by < 100 m during a diel cycle, and 3) non-migrators. Swimbladders Determination of functional swimbladder presence or absence was derived through several sources including: Denton and Marshall (1958) for Gonostoma elongatum, Marshall (1960) for Maurolicus muelleri, Brooks (1977) for Anoplogaster cornuta, sternoptychid symbols (Table 1) 3, 4, and 6, and myctophid symbols (Table 1) I, J, O, R, T, U, V, w, X, Y, and z, Hopkins and Baird (1985) for Sternoptyx pseudobscura, J.V. Gartner Jr. (pers. comm.) for Bathylagus longirostris, and T.M. Lancraft (pers. comm.) for Cyclothone pallida. Information on swimbladder presence or absence was not available for all species.

PAGE 22

TABLE 1. List of family, genus and species, symbol(SYM), migration, depth ranges, depth of occurrence (MOO), standard length (SL), wet weight (WW), water, ash-free dry weight (AFDW), and skeletal ash (SA). NuMbers in parentheses below water, AFDW, and SA values are standard error of the mean, and the number of individuals analyzed. Abbreviations are as follows: S=surface, g=grams, DW=dry weight, WM=weak migrator, NM=non-migrator, M=migrator, and ND=data insufficient for determination. (Brackets) indicate migration pattern is uncertain. FAHIL Y Day/Night Mean SL(-) Mean W(g) WATER AFDW SA Genus and species SYH Migration Range (m) MOO (m) (range SL) (range WW) (XWW) (XDW) (XWW) ANOPLOGASTERIDAE Anoplogaster cornuta A [NHl 600-950 1/ND 600 86.5 32.8 88.1 77.1 1.1 (72.0-101.0) (20.7-45.0) (1.9;2) (3.9;2) (0.3;2) BATHYLAGIDAE Bathylagus longirostrls B (1./141 ND/180-200 1 200 90.8 6.8 86.7 76.5 1.9 (42.0-117.0) (0.5-11.3) (0.1;6) (1.8;6) (0.3;6) GONOSTOHATIDAE Cyclothone pallida c [NHl 430-690 1!430-690 500 42.2 0.5 81.6 67.6 4 7 (36.5-49.0) (0.4-0.1) (1.5;4) (4.4;4) (1.2;4) Gonostoma elongatum 2 D M 425-725/25-325 140 107.9 4.1 85.9 67.9 3.0 (85.0-121.0) (0.9-12.7) (1.0;14) (0.9;13) (0.2;13) HELAHPHAIDAE Helamphaes longivelis E [14] 800 1t130 1 150 20.0 0.2 78.7 65.6 5.9 Poromitra sp. F [14] 800 1100 3t150-5S0 3150 15.0 0.1 84.6 70.6 2.8 Scopelegadus mizolepis G [14] 800-1000/400-600 500 47.6 3.6 88.0 67.7 3.0 mizolepis (31.0-64.0) (0.5-6.9) (1.9;6> (2.2;6) (0.1;6) Scopeloberyx sp. H [NHl 700-1000 1 t700-1000700 22.0 0.2 77.3 90.2 1.1 MYCTOPHIDAE Benthosema suborbitale 14 400-600/50-105 50 20.6 0.4 66.7 80.4 5.4 (18.7-22.5) (0.3-0.5) (3.7;2) (3.0;2) (1.6;2) 0

PAGE 23

TABLE 1. (Cont'd). FAMILY Day/llight Mean Sl(-) Mean W(g) WATER AFDW SA Genus and species SYM Migration Range (m) MOO (m) (range SL) (range WW) (XWW) (XOW) (XWW) Bolinichthys J M 550-700/50-250 50 36.8 1.0 76.2 75.9 4.0 (21.0-49.0) (0.4-1.8) ( 1.4;4) (1.9;4) (0.5;4) Centrobranchus nigroocellatus J( M 400-550/S150 s 24.0 0.19 13.1 69.5 5.5 Diaphus dumerilii L M 300-600/50-155 50 36.1 0.9 16.1 16.1 4.9 (23.5-48.0) (0.3-1.1) (1.3;6) (1.4;6) (0.4;6) D. effulgens M M 300-500/100-3307 !,100 39.6 1.7 76.8 75.2 3.4 (24.0-57.0) (0.2-3.9) (0.7;5) (4.1;5) (0.9;5) D. lucidus N M 450-1000/50-300 50 50.5 2.1 75.6 81.4 3.7 (45.0-55.0) ( 1.5-2. 7) (1.6;6) (1.9;6) (0.6;6) D. moll is 0 M 300-1000/50-225 50 31.4 0.6 73.3 76.0 5.7 (18.0-39.0) (0.3-0.9) (1.6;5) (4.5;4> (1.5;5) D. splendidus p M 300-600/50-250 50 42.5 1.3 74.2 72.7 6.5 (28.0-57.0) (0.2.4) (1.2;2) (8.3;2) (2.8;2) Gonichthys COCCO Q M NO/S s 34.7 0.4 70.0 69.8 8.1 (23.0-43.0) (0.1-0.6) (0.1;3) (3.3;2) (1.6;2) Hygophum benoiti R M 300-700/0-250 s 18.0 0.1 64.5 75.5 6.0 H. reinhardtii s M 550-700/0250 s 31.0 0.3 70.7 86.2 2.9 Lampadena luminosa T M 500 ->1000/65-350 75 43.6 1.8 77.1 70.9 5.7 (22.3-67.0) (0.3-4.2) (1.0;4) (2.1;4) (0.9;4> Lampanyctus a latus u M 550-700/80-200 75 36.0 0.6 78.9 77.3 4.2 (21.7-46.0) (0.28-1.1) (0.6;8) (1.0;7) (0.4;1) L lineatus v M 400 -1000/80-1000 >100 58.5 1.5 88.3 65.3 2.4 (48.0-70.0) (0.7-1.6) (0.9;4) (2.7;4) (0.6;4) Lepidophanes guentheri M 400-900/75-155 75 38.4 0.8 78.2 72.6 5.0 (28.0-51.0) (0.3-2.4) (1.1;10) (2.1;11) (0.6;11)

PAGE 24

TABLE 1. (Cont'd). FAMILY Day/Might Mean SL<-> Mean W(g) WATER AFDW SA Genus and species SYM Migration Range (m) MOO (m) (range SL) (range WW) (XWW) (XOW) (XWW) Lobianchia gemellarii X M 300-450/75-210 75 20.5 0.5 72.9 68.8 7.4 ( 19.5-21.5) (0.4-0.6) (3.4;3) (0.6;3) ( 1.0;3) Myctophum nitidulum y M NO/S-50 s 53.0 2.7 74.9 79.4 4.1 (35.0-65.0) (0.6-4.6) (1.4;3) (2.9;3) ( 1.0;3) Notoscopelus resplendens z M N0/50-250 50 49.1 2.0 73.5 79.5 4.6 (40.0-56.0) (0.1-2.3) (0.5;7) (2.2;7) (0.5;7) Notolychnus valdiviae 2 M 400-500/50-155 50 18.0 0.1 n.1 88.0 2.6 (17.5-18.5) ( 0. 1) (2.7;2) (2.6;2) (1.0;2) Taaningichthys bathyphilus 2 NM 600->1000/900 600 54.0 1.5 79.1 88.5 2.0 STERNOPTYCH I OAE Argyropelecus aculeatus 3 M 160-500/145-300 145 33.1 1.9 79.8 70.2 4.9 (13.0-55.0) (0.2.8) (0.5;21) (1.0;19) (0.3;19) A. hemigymnus 4 WM 350-600/300-500 300 26.1 0.7 76.2 68.9 6.2 (17.5-25.0) (0.3-1.2) (1.0;4) (1.6;4) (0.5;3) Maurolicus muelleri 5 NO NO 30.5 0.3 71.2 68.8 8.0 (29.0-32.0) (0.27-0.4) (1.0;2> (2.4;2) ( 1.0;2) Sternoptyx diaphana 6 NM 500-800/500-900 500 25.3 1. 7 81.2 70.9 5.2 (16.0-37.0) (0.4-3.6) (0.5;8) (3.5;7) (0.3;8) S. pseudobscura 7 NM 800-1000/800-1000 800 33.4 3.5 86.7 72.6 2.7 (27.0-39.0) (1.6-5.5) (1.6;5) (3.3;5) (0.8;4) depth distributions are uncertain 2 data suggests all members are migratory 3 Keene et al., 1987 for Poromitra sp.

PAGE 25

13 Compositional data were expressed as percent of ww and percent ash-free dry weight(% AFDW). As concluded by Childress (1977), AFDW (% DW) represented partitioning of organic matter, and was therefore useful in conceptualizing adaptive strategies in energy utilization. Wet weight was superior in its representation of the ecological and physiological state since it was the "live state" and accounted for the entire body weight (Childress, 1977). Data as% WW and % AFDW allowed for comparisons with other proximate analysis investigations. Statistics Statistical manipulations were performed using Statgraphics (version 1.1, STSC INC., Rockville, Maryland). Regressions, mean values, and the MannWhitney-Wilcoxon Test were performed on 21 species of fishes which had 2, and whose depth distributions appeared certain (except where noted) The statistical tables of Rohlf and Sokal (1969) provided critical values for the correlation coefficients and the student's t-distribution. Values are reported for regressions as significant at P<0.05 (unless noted

PAGE 26

otherwise), with slopes and mean values 95% confidence limits. 14

PAGE 27

1 5 RESULTS Water content Water content of fishes ranged from 64.5% to 88.1% WW (Table 1) Six of the thirty-three species examined had water contents >85.0% wet weight. Three of these were categorized as weak migrators or non-migrators. Nonmigrators and weak migrators had a mean water content of 82.8% WW ( 5.9, n=5) while migrators had a mean water content of 77.6% WW ( 3.1, n=16). Water content in the two groups was somewhat different ( Mann-Whitney-Wilcoxon Test: z=1.73, 0.05
PAGE 28

16 90 -.v G A .... J: 86 D w .... w 82 .c a .... 78 z w 4 .... W = 60.56 D o.oso.o3 z 0 74 R2= 0.51 (.) a: 95%CL= 0.03 w .... 70 < 66 0 200 400 600 800 MINIMUM DEPTH OF OCCURRENCE (m) Fig. 1. Regression of water content (% wet weight) on minimum depth of occurrence (MOO) in 21 species of midwater fishes from the Gu0f of Mexico. Equation for the regression is W=60.56D 05 0 03 where W=water content and D=depth (significant at P
PAGE 29

89 _, A = 86.69 D -0.03 0.03 85 R2=0.22 -95% CL=0.03 ..... J: eN -\ u a: 77 A c ,o #. J eM 73 p c w 7e u. < r 3 6 69 x e4 .o ,c G 65 .v 0 200 400 600 800 MINIMUM DEPTH OF OCCURRENCE (m) Fig. 2. Regression of ash-free dry weight (% dry weight) on minimum depth of occurrence (MOO) in 21 species of midwater fishes from the Gulf of Mexico. Eauation fgr the regression is A=86.69D-o.o3 0 3 where A=ash-free dry weight and D=depth (significant at P<0.05). 17

PAGE 30

18 to have functional swimbladders (Table 1, symbols I-J, o, R, T-Z, and 1-8) ranged from 2.0-8.0% ww (mean=4.8 .4, n=18). Those without swimbladders (Table 1, symbols, A-D) had skeletal ash values ranging from 1.1-4.7% ww (mean=2.7 2.5; n=4). Differences between the two groups were not significant. Lipid Lipid content varied from 4.3 to 43.3% AFDW and from 0.6 to 10.7% WW (Table 2). An exception to the low lipid content in most species was Notoylychnus valdivae which had a markedly high lipid content (43.3% AFDW .7 and 10.7% ww + 1.3; n=2). There was no apparent correlation between lipid content (expressed as % AFDW or % WW) with MOO. The lipid content of migrators when compared with that of nonmigrators and weak migrators was not significantly different whether expressed as % AFDW or % ww. Fishes without swimbladders had a mean lipid content of 10.7 % AFDW ( 4.6; n=4) while fishes with swimbladders had a mean lipid content of 10.0% AFDW (+ 4.2; n=18). Lipid content (% AFDW) in the two groups was somewhat different (Mann-Whitney Wilcoxon Test: z=1.92, 0.05
PAGE 31

TABLE 2. List of faily, genus and species, lipid content and protein content and carbohydrate content -1 and X carbon hydrogen nitrogen and caloric content (Kcal 100 g >-Numbers in parentheses are (standard error of the mean,and the number of individuals analyzed. Abbreviations are as follows: dry weight, weight, g=grams, CHOacarbohydrate, Cacarbon, H=hydrogen, N=nitrogen, and Kcal=kilocalorles. FAMILY Genus and species ANOPLOGASTERIDAE Anoplogaster cornuta BATHYLAGIDAE SYM A 15.0(1.0;2) 1.5(0.9;2) Bathylagus longirostris B 9.1(2.0;6) 0.9(0.2;6) GONOSTOMATIDAE Cyclothone pallid& Gonostoma elongatum MELAMPHAIDAE3 Melamphaes longivelis Scopelegadus mizolepis mizolepfs Scopeloberyx sp. MYCTOPHIOAE c 8.9(1.4;3) 1.0(0.2;3) 0 9.9(1.6;10) 1.6((0.8;10) E 10.4 1.4 G 8.5(0.4;6) 1.4(0.3;6) H 11.8 2.5 Benthosema suborbitale 6.0(1.3;2) 1.6(0. 1;2) Bolinichthys photothorax J 7.0(0.2;4) 1.0(0.5;4) Centrobranchus nigroocellatus 4.3 K 0.8 52.3(0.3;2) 4.9(1.0;2) 64.6(1.5;6) 6.4(0.4;6) 75.3(11.4;3) 8.5(1.2;3) 70.0(2.3;13) 6.9(0.7;13) 71.3 9.5 71.1(3.8;6) 5.8(0.9;6) 72.3 14.8 46.1(4.2;2) 11. 7(0.3;2) 73.2(3.1;4) 13.4(0.4;3) 43.1 7.9 0.9(0.5;2) 0.1(0.0;2) 1.0(0.1;6) 0.1(0.0;6) 0.8(0.2;3) 0.1(0.0;3) 1.0(0.0;12) 0.1(0.1;12) 0.7 0.1 1.0(0.2;6) 0.1(0.0;6) 0.3 0.1 0.6(0.2;2) 0.2(0.1;2) 1.0(0.3;4) 0.2(0.1;4) 1.0 0.2 50.7 (2.7;4) 54.8 51.7 (1.0;4) 49.1 54.6 (4.1;3) 47.6 51.1 (1.5;3) H(1AFDW) 7.6 (0.3;4) 7.9 8.2 (0.4;4) 6.7 8.2 (0.6;3) 7.7 7.7 (0.2;3) M(XAFDW) 13.2 (0.7;4) 15.1 15.1 (0.5;4) 11.7 15.1 ( 1.4;3) 13.1 14.6 (0.2;3) Kcal 100 g 1 41.4 44.7 57.6 53.7 66.7 45.7 106.5 81.4 85.9 52.8

PAGE 32

TABLE 2. (Cont'd). FAMILY SYM LIPID(lAFDY) PROTEU(lAFDY CHO(lAFDY) C(lAFDY) M(lAFDY) 0.8(0.1;2> 54.2 7.6 14.6 89.9 1 .2(0.1;2) 13.8(0.1;2) 0.2(0.0;2) Gonichthys COCCO Q 5.7(0.5;3) 66.4(7.8;2) 0.6(0.2;2> 49.2 8.2 15.2 91.0 1 .3(0. 1 ;3) 13.9(1 .2;2) 0.1(0.0;2) (4.1;2) (0.5;2) (1.1;2) Hygophum benoitii R 13.4 40.8 1.5 95.1 3.6 10.9 0.4 H. reinhardtii s 10.0 59.3 0.9 49.4 7.7 12.8 105.2 2.5 14.5 0.2 Lampadena luminosa T 6.7(0.3;3) 69.2(7.0;4> 1.0(0.1;4) 53.3 7.9 15.1 73.4 1.0(0.02;3) 11 .2( 1 .2;4) 0.2(0.0;4) Lampanyctus a latus u 7.8(0.5;7) 77.3(2. 7;7) 1.0(0.0;7) 51.5 7.8 14.3 91.7 1.4(0.1;7) 13.8(0.9;7) 0.2(0. 1;7) (2.6;5) (0.3;5) (0.4;5) L. l i neat us v 6.6(0.4;4) 77.9(6.9;4) 1.0(0.1;4> 53.1 7.8 15.0 41.0 0.6(0.3;4) 6.2(0.7;4) 0.1(0.0;4) (1.5;2) (0.4;2) (0.1;2) Lepidophanes guentheri IJ 7.3((0.6;10) 74.0(2.6;11) 0. 7(0.1; 10) 53.2 7.9 15.3 81.8 1 .3(0. 1; 10) 12.3(0.8; 1 1) 0.1(0.0;10) Lobianchia gemellarii X 8.3(1. 7;2) 62.1(5 .2;2) 1.0(0.1;3) 50.8 7.7 13.9 68.9 1 .6(0.6;2) 9.5(1 .0;2) 0.2(0. 1 ;3) Myctophum nitidulum y 7 .2( 1.2;3) 63.4(5.4;3) 0. 7(0.1 ;3) 46.3 7.8 13.7 75.9 1 .4(0.3;3) 11.1(2.9;3) 0.1 (0.0;3) [\) 0

PAGE 33

TABLE 2. (Cont'd). FAMILY SYM Lipid 13.2(0.7;7) 0.2(0.0;6> (1.0;3) (0.1;3> (1 .0;3) Notolychnus valdiviae 43.3(6.7;2) 32.11(3.3;2) 50.8 7.2 8.0 142.7 10.7(1.3;2) 8.7(1.0;2> Taaningichthys bathyphi lus 9.9 52.2 1.1 71.2 2 1.8 9.6 0.2 STERNOPTYCHIDAE Argyropelecus aculeatus 3 8.4(0.9;18) 80.6(2.5;21) 1.2(0.1;19) 52.4 8.3 16.2 73.9 1 .0(0.2; 17) 11.3(0.4;21) 0.2(0.0;19) (5.7;9) (0.9;9) (2.0;9) Argyropelecus hemigymnus 4 6.5(0.7;3) 66.1(9.0;3) 1.2(0.1;3) 50.6 7.8 15.5 72.0 1.1(0. 1;3) 10.8(2.0;3) 0.2(0.0;3) (3.1;3) (0.4;3) (0.8;3) Maurolicus muelleri 5 6.9(1.8;2) 75.2(10.0;2) 0.9(0.0;2> 97.9 1.4(0.4;2> 14.9(2.0;2> 0.2(0.0;2> Sternoptyx diaphana 6 11.4(0.7;8) 73.2(2.7;7) 1.3(0.1;11> 52.9 7.6 15.7 68.5 1.1(0.1;8) 10.2(0.5;8) 0.2(0.0;8) (9.1;3) (1 .2;3) (2.6;3> s. pseudobscura 7 9.0(0.4;4> 67.5(4.3;4) 1.4(0.2;4> 49.9 7.2 12.4 52.8 1 .0(0. 1;4) 7.6(0.8;4) 0.2(0.0;4) (3.2;2) (0.2;2> (2.7;2> Poromitra sp.-insufficient sample for determination of chemical composition. 1\)

PAGE 34

Protein Protein content varied from 4.9 to 14.9% ww (Table 2). On a wet weight basis, protein decreased with MOO (Fig.3). Vertical migrators had a mean protein content of 11.0% ww 22 ( 1.1, n=23) while non-migrators and weak migrators had a mean protein content of 9.1% WW ( 2.5, n=8). Protein content in the two groups was somewhat different (MannWhitney-Wilcoxan-Test: z=-1.86, O.OS
PAGE 35

1 4 9 rr------------------1-J: ijj12.9 1w 10.9 Iz w !z 8.9 X 1 p = 26.23 0 -0.20.11 R2=0.44 95% CL= 0 1 1 .s I I I 0 .c ,) (.) z -w 0 I6 9 0 cr v Q. G 4 9 A 0 200 400 600 800 MINIMUM DEPTH OF OCC U RRENCE (m) Fig. 3. Regression of protein content (% wet weight) o n minimum depth o f occurrence (MOO) in 21 species of midwater fishes from the Gulf of Mexigo1 Equation for the regression is P=26.23D-20 1 where P =protein and D =depth (significant at P <0.01). 23

PAGE 36

24 Caloric content Caloric content expressed as Kcal 100 g ww-1 decreased significantly with MOO (Fig.4). Migratory species had significantly higher caloric contents, which ranging from 41.0 to 142.7 Kcal 100 g ww-1 (mean=79.7 Kcal 100 g ww-1 12.5) than non-migrators and weak migrators which ranged from 41.4 to 72.0 Kcal 100 g ww-1 (mean=58.5 Kcal 100 g ww-1 15.3, Mann-Whitney-Wilcoxon Test: Z=-2.19, P<0.05). Depth related trends in caloric content mirrored trends in protein as % WW. The decrease in caloric content (as represented by lipid and protein) with depth appeared distinct from buoyancy mechanisms because it occurred in fishes with well developed swimbladders as well as in those species without them. Carbon carbon as %AFDW ranged from 46.3 to 54.8%. There was no apparent trend with increasing MOO. Carbon content correlated well with protein content (equation for the regression is C=45.29 + o.o9P 0.01 where C=carbon (% AFDW) and P=protein (% AFDW); n=20; P<0.05).

PAGE 37

25 -I 160 J: C = 204.89 0 -0.22.10 w 140 ., R2=0.50 95%CL=0.10 w 120 0 0 0 ._ as 100 N CJ p .u o,J z 80 w Te M e4 z 0 x .a (.) eo (.) 0 C a: 7. 0 G 40 A < (.) 0 200 400 600 800 MINIMUM DEPTH OF OCCURRENCE (m) Fig. 4. Regression of caloric content (Kcal 100 g ww-1 ) on minimum depth of occurrence (MOO) in 21 species of midwater the Gulf o! for the regress1on 1s C=204.89D 0 0 where C=caloric content and D=depth (significant at P
PAGE 38

26 Hydrogen Hydrogen as a percentage of ash-free dry weight ranged from 6.7 to 8.3%. There was no apparent trend with increasing MOO. Hydrogen content did not correlate with either protein or lipid content. Nitrogen Nitrogen content ranged from 7.2 to 16.2% of AFDW. Variation in nitrogen content was largely accounted for by variation in protein content (Fig.5; n=20).

PAGE 39

82 (!J P = -3.80+5.01 N .v -.u w R 2 = 0.72 c. w > 72 Je .e a: 95% CL=1.54 P eG 0 .7 ar-o w a: 62 Lt m < -52 .... I z 0 u 42 z w .... 0 32 7.2 9.2 11.2 13.2 15.2 17.2 NITROGEN(% ASH-FREE DRY WEIGHT) Fig. 5. Regression of protein content (%AFDW) on nitrogen content (%AFDW) in 20 species of midwater fishes from the Gulf of Mexico. Equation for the regression is P=-3.80 + 5.01N 1.54 where P=protein content and D=depth (significant at P
PAGE 40

DISCUSSION Differences in the hydrography, productivity, and faunal composition of midwater systems are central to understanding compositional differences among species of different regions. The eastern Gulf of Mexico and other areas that have been previously examined, e.g., the California Current, the eastern North Pacific gyre, and the transition region between the latter two areas, are dramatically different. The eastern Gulf of Mexico and north Pacific gyre are similar in that they are stable, warm water areas with high faunal diversity, low standing stocks and a primary productivity of approximately 50 g C m-2 y-1 (Nowlin, 1971; McGowan and Williams, 1973; McGowan, 1974; Hopkins, 1982; 28 Cullen and Eppley, 1981; Gartner et al, 1987). Fauna of the California current and eastern North Pacific gyre are similar with greater diversity in the gyre and higher standing stocks in the california current (Barnett, 1983; Bailey and Robison, 1986). The California current is a colder, more variable system with a mean primary productivity (-150 g c m-2 yr-1 ) approximately three times that of the eastern North Pacific gyre (McGowan and Williams, 1973; McGowan, 1974; Cullen and Eppley, 1981;

PAGE 41

Bailey and Robison, 1986). Midwater fishes of the eastern Gulf of Mexico show variable water content, high protein content, low lipid 29 and relatively low caloric content. These trends are characteristic of midwater fishes from geographical areas of low productivity (Bailey and Robison, 1986), whereas high lipid and caloric content are associated with high productivity areas (Childress and Nygaard, 1973). The primary focus for proximate analysis of eastern Gulf of Mexico fishes is to characterize the chemical composition and relate it to habits and adaptations specific to this system. Eastern Gulf of Mexico fishes may be thought of as members of a strongly migrating community that experiences high temperatures and minimum seasonality. Observed low lipid values may reflect an absence of need for energy reserves, or an inability to accumulate these reserves. Food availability, though low, is not strongly cyclic, eliminating the need for large energy depots. In contrast, the high metabolic costs associated with residing part of the day at high surface temperatures may preclude lipid deposition. Low lipids and high protein in Gulf fishes support a reduced requirement for energy reserves and an increased need for muscle mass related to migration. The relatively high seletal ash (% WW) found in eastern Gulf of Mexico fishes, in addition to high protein values, supports the idea of a more robust nature in fishes which

PAGE 42

30 are miqrators. Hiqh protein content in Gulf miqrators suqqests that protein content correlates both with increased liqht at depth and increased importance of visual predation, rather than food availability (Bailey and Robison, 1986). The increase in water content in deeper livinq species from the eastern Gulf of Mexico is similar to that observed in deep livinq species from the California current, and Transition water between the eastern north Pacific qyre and the California current, but different from the qyre where no depth related trends in water content were observed (Childress and Nyqaard, 1973; Bailey and Robison, 1986). Reqressions of water content on MOO for fishes from the eastern Gulf of Mexico (W=60.56o 0 054 ) and eastern N. Pacific transition water (W=58.89o 0 055 ; Bailey and Robison, 1986), had similar slopes. Substitution of dilute body fluids for orqanic matter has been cited as a means of achievinq neutral buoyancy, of reducinq enerqy required per unit qrowth, or as an end result of low food availability (Childress, 1973; Bailey and Robison, 1986). The decline in AFOW (%OW) with MOO in Gulf species contrasts with the absence of such a trend in California current species (Childress and Nyqaard, 1973). Mean AFDW for Gulf species (74.7% ow 2.4; n=33) was lower than that of california current species (82.8% OW 2.0; n=29; Childress and Nyqaard, 1973) and eastern N. Pacific qyre species (87.2 2.0; n=12; Bailey and Robison, 1986). The hiqh end of the ranqe for AFOW (%OW) was comparable between

PAGE 43

3 1 California Current and gyre species while the low end of the range was less in Gulf species than in current or gyre fishes (65.3 to 90.2% AFOW; 73.8 to 92.1% AFOW; 81.3 to 93.7% AFOW, respectively; Childress and Nygaard, 1973; Bailey and Robison, 1986). A consistent pattern was not apparent in AFOW (%OW) of the same species or congeners from different systems (Table 3). The AFOW of the deep dwelling, non-migratory fish, Anoplogaster cornuta is essentially identical between the eastern Gulf of Mexico (77.1% OW) and California current (77.5% OW; Childress and Nygaard, 1973) specimens. However, AFOW differed markedly for the non-migrator, sternoptyx diaphana from the eastern Gulf of Mexico (70.9% OW) when compared to that of the same species from the eastern N. Pacific gyre (81.3%0W; Bailey and Robison, 1986). The AFDW values of non-migrating Cyclothone congeners, pallida (67.6% DW), from the eastern Gulf of Mexico and c.acclinidens (88.8% OW), from the eastern North Pacific gyre also differed. Part of the discrepancies in AFOW between species of the different systems may be methodological in origin. Ash-free dry weights were determined in Gulf species in a low-temperature asher, as opposed to ashing in a high temperature (500o C) muffle furnace. The low-temperature asher was chosen because it has been shown to minimize error. childress and Price (1983) showed that a low temperature asher underestimates the ash-free weight by 1.8%

PAGE 44

OW, in contrast to the muffle furnace which overestimates by 8.6% ow. 32 A significant difference in skeletal ash (%WW) between eastern Gulf of Mexico species with functional swimbladders and those without functional swimbladders was not found. This is in contrast to midwater fishes of the California current where skeletal ash values (%WW) for the two groups were significantly different (Childress and Nygaard, 1973). The mean values of skeletal ash (%WW) for eastern Gulf of Mexico species with functional swimbladders (4.8 0.8, n=18) and without swimbladders (2.7% 2.5, n=4) compared to values for the similar groups in species from the California Current (3.3 1.03, n=4; 1.8% 0.4, n=22 respectively, Childress and Nygaard, 1973) are not significantly higher, P<0.01. An explanation for the relatively high skeletal ash in Gulf species is not readily apparent, unless it is an indication of a more robust skeletal structure. Fishes that are shallow living, or that migrate into shallow waters, appear to have higher skeletal ash content (Childress and Nygaard, 1973). The hatchetfishes, Argyropelecus aculeatus hemigymnus, have a lower mean water content (78.0% WW) and higher mean ash content (5.5% WW) than their deeper living confamilials, sternoptyx diaphana and s.pseudobscura (84.0% ww, 4.0% WW respectively). Argyropelecus aculeatus, a migrator, has a higher protein content (11.3% ww; 80.6% AFOW) than the other three species

PAGE 45

33 which are weak migrators or non-migrators. Midwater fishes that achieve neutral buoyancy by means of a gas filled swimbladder are reported to be high in protein (8.0-15% WW), low in lipid (0.6-4.3% WW), low in water (60.0-83.0% WW), and high in skeletal ash (2.5-5.8% WW) (Childress and Nygaard, 1973). Many of the Gulf migrators have values in these ranges. A greater percentage of species examined from the eastern Gulf of Mexico have functional swimbladders than those examined from the California current (Childress and Nygaard, 1973). Species in the Gulf of Mexico may rely more heavily on swimbladders and dilute body fluids for achieving neutral buoyancy than species from other systems which have higher lipid contents. The general trend of decreasing skeletal ash (% WW) with depth suggests a means for achieving neutral buoyancy in deeper living fishes of the eastern Gulf of Mexico. The lipid component of organic content is low in most eastern Gulf of Mexico species, particularly when compared with values in midwater fishes from cold waters (Table 3; Fig. 6). Electrona antarctica, Bathylagus antarcticus, and Gymnoscopelus nicholsi, three common mesopelagic species from the Antarctic had total lipid contents of 51.1% ow, 17.1% WW and 61.3% OW, 20.7% WW, n=2; 23.3% ow, n=1 and 72.8% ow n=1, respectively (Reinhardt and van Vleet, 1986). The profound differences in lipid content between polar and tropical-subtropical midwater fishes may be attributed to the character of lipid deposition in the

PAGE 46

Table 3. Comparison of cheical composition with data fro other Investigators on congeneric fishes. SPECIES MDO(m) Mean WW(g) WATER AFDW LIPID LIPID PROTEIN PROTEIN Keel 100 g REFERENCE (range WW) (lWW) (lOW) (lAFDW) (lWW) (lAFDW) (lWW) ww1 Anoelosaster cornuta 600 32 8 88.1 77.1 15. 0 1.5 52.3 4.9 41.4 Sti ckney 1987 (20.7.0) (1.9;2> (3.9;2> (7. 0 ;2) (0. 9;2) (0.3 ;2> (1.0;2) Eastern Gulf of Mexico Anoelosas!er cornuta 550 NO 85.0 77 5 24.1 NO 52.6 NO 61.7 Childress and Nygaard 1973 (27.0.0) (1.34;2> (3.2;2) (2.9;2) (0.9;2) San Clemente Basin coast of Southern California diaehana 500 1.7 81.2 70 9 8 4 1.1 73.2 10.2 68.5 Stickney 1987 (0.4-3.6) (0.5;8) (3.5;7) (0.7;8) (0.1;8) (2. 7;7) (0.5;8) dlaebana 500 0.3 83.4 81.3 10. 9 1.4 67.5 9.0 63.7 Bailey and Robison 1986 (0.1 0 .5) (0.9;18) (0.9;18) (1.1;18) (0.1;18) (2.2;18) (0.4;18) Eastern N. Pacfffc gyre eallida 500 0.5 81.6 67.6 8 9 1.0 75.3 8.5 57.6 Stickney 1987 (0.4-0.7) (1.5;4) (4.4;4) (1.4;3) (0.2;3) (11.4;3) (1.2;3) acclinidens 500 0 5 77.2 88.8 36 2 7 3 43.9 8.9 115.0 Bailey and Robison 1986 (0.1-1.1) (1.2;10) (0.8;10) (1.1;10) (0.4;10) (0.7;10) (0.6;10)

PAGE 47

..... J: w 3: ..... w 3: ..... z w ..... z 0 () 0 g; ..J 18 16 14 12 10 8 6 4 2 0 0 \ \ \ \ \ \ ................................. ....... -CALIFORNIA CURRENT (BAILEY AND ROBISON). CAUFORNIA CURRENT (CHILDRESS AND NYGAARD). TRANSITION (CALIFORNIA CURRENT EASTERN N PACIFIC GYRE). EASTERN NORTH PACIFIC GYRE. EASTERN GULF OF MEXICO ----------------------------200 400 600 800 1000 1200 MINIMUM DEPTH OF OCCURRENCE (m) F ig. 6. Comparison of regression curves of lipid content (% wet weight) on minimum depth of occurrence (MOO) in midwater fishes from: the California Current (Bailey and Robison, 1986 significant at PO.OS); the Eastern N. Pacific gyre (Bailey and Robison, 1986, not significant, P>O.OS); the Eastern Gulf of Mexico (Stickney, in prep., not significant, P>O.OS). 35

PAGE 48

36 two regions, rather than as a result of methodological differences. In copepods, wax esters replace triglycerides as the dominant lipid component in species living in cold temperature or at depths greater than 625 meters (Lee et al. 1971). The high temperatures encountered by tropical epipelagic fishes are suggested as inhibitory to lipid deposition (Lee et al., 1971 while lipogenesis is generally higher in cold acclimated fishes (Reinhardt and Van Vleet, 1986). A comparison of lipid content in three myctophid fishes (MOO 50-75 m) from three markedly different systems, Electrona antarctica from the Antarctic (18.9% WW), Lampanyctus ritteri from the California current (11.8% WW) and Lampanyctus alatus from the eastern Gulf of Mexico (1.4% WW) is an example of the markedly low lipid content in fishes from the eastern Gulf of Mexico. The high lipid deposition found in cold water species may be related to the long-term energy reserves necessary for overwintering (Reinhardt and Van Vleet, 1986). Diet may be important in determining the low lipid content observed in Gulf of Mexico species since the lipid contents of predators may mirror that of their prey (Love, 1970; Reinhardt and van Vleet, 1986). In some cases, fatty acid composition of lipid reserves in predators has been shown to reflect that of prey species (Sargent, 1976). However, internally synthesized fatty acids also contribute to the pattern of fatty acids in depot lipids and a good

PAGE 49

correlation between dietary lipid and depot lipid generally cannot be made (Sargent, 1976). Specific fatty acid patterns are not considered here, but there are data on lipid content and vertical distribution of principal 37 prey items which may be informative on the relation of lipid content in predators and prey. The principal taxonomic components of the midwater fish community in the Gulf, the Myctophidae, Gonostomatidae, and Sternoptychidae, forage primarily on copepods and euphausids (Hopkins, 1982). The family containing the largest number of species examined, the Myctophidae, are primarily centered between 50-150m at night (Gartner, et al., 1987) where copepods, euphausiids, and ostracods dominate the biomass (Hopkins 1982, Hopkins, pers. comm.). Low lipid values were observed in the euphausiids (6.8 to 7.3% OW) and copepods (6.8 to 7.8% OW; Morris and Hopkins, 1983; Hopkins, pers. comm.). Only two zooplankton species with lipid contents >27% OW were found in the eastern Gulf of Mexico: Eucalanus monachus (56.3 %OW) generally abundant below 550 m, and Rhincalanus species, predominantly R.cornutus, abundant throughout the entire upper 1000 m, day and night (lipid content of 48.8% OW; Morris and Hopkins, 1983; Hopkins, 1982). The 50 to 150m zone inhabited by most myctophids at night is not the zone of maximum caloric density or maximum caloric content per prey individual, which occurs shallower than 50 m (Hopkins, 1982)

PAGE 50

38 Most mesopelagic species studied reside between 350 and 700 m during the day where again euphausiids, copepods, and ostracods dominate the biomass (Hopkins, pers. comm.). Lipid values are low (3.9% ow to 4.6% DW) with the exception of Eucalanus, which became an increasingly important part of the biomass at depths greater than 400 m, and Megacalanus princeps (19.8% DW) and Rhincalanus (Morris and Hopkins, 1983; Hopkins, pers. comm.) which represented important biomass components below 700 m. Myctophids which are reported to feed primarily at night (Hopkins, 1982) may not be utilizing the higher caloric content zooplankton. Both Lampanyctus alatus, a dominant, subtropical, myctophid (Gartner et al., 1987) and elongatum, an abundant gonostomatid in the eastern Gulf of Mexico have diets selective for the low lipid content copepod genus Pleuromamma (Hopkins and Baird, 1985). Other species from the present study with reported prey items which appear low in lipid content, are Diaphus dumerilii, Lepidophanes guentheri. Gonostoma elongatum, Argyropelecus aculeatus, Benthosema suborbitale, Sternoptyx diaphana, and Sternoptyx pseudobscura (Morris and Hopkins, 1983; Hopkins and Baird, 1977). There were several exceptions to correlations of low lipid content between predator and prey. Notolychnus yaldiyiae, showed high lipid levels (43.4% AFDW; 10.7% WW), but feeds on prey CPleuromamrna, oncaea, conchoecinae (ostracod) and euphausiid larvae) some of which are known to

PAGE 51

39 have low lipid content (Morris and Hopkins, 1983; Hopkins 1982) Sex was not determined for Notolychnus valdiviae, therefore, high lipids may be related to reproductive effort of females. Another exception is the hatchetfish, Argyropelecus aculeatus which was low in lipid content, but feeds heavily on the lipid rich copepod, Eucalanus monachus (Hopkins and Baird, 1985). Since most of the fishes examined vertically migrate, similarity of lipid content between shallow and deep dwellers may reflect similar prey items, although most prey items also migrate (Hopkins, 1982) Low lipid values for most species suggest the possibility that reserves are unnecessary in a stable system. In a tropical-subtropical system, a constant food supply is available in the form of zooplankton (Hayward and McGowan, 1979) lessening the need for lipid reserves. Large wax ester reserves are typically seen in species from cold water systems where food availability is strongly dependent on season (Sargent, 1976). Herbivorous plankton do not abandon surface layers in tropical systems since seasonal changes are minimal and therefore, they serve as a more stable food supply (Vinogradov and Tseitlin, 1983). Decreasing protein content (%WW) with depth in Gulf of Mexico fishes supports previous studies (Childress and Nygaard, 1973; Bailey and Robison, 1986). Somewhat higher protein values (% WW) were observed in migrators than in non-migrators and weak migrators in the eastern Gulf of

PAGE 52

Mexico species. A correlation between protein content and the need for increased locomotory abilities is supported by the generally higher values found in migrators. The locomotory demands associated with vertical migration require greater muscle mass. The differences in protein content, as muscle mass needed for locomotion, between migratory fishes and deep dwelling non-migrators are independent of any enzymatic differences between the two groups (Childress and Somero, 1970; Torres et al, 1979). 40 As with other studies (Childress and Nygaard, 1973; Bailey and Robison, 1986), protein (% AFDW) does not show a trend with MDO in eastern Gulf of Mexico fishes. A weak but significant increase in protein (% AFDW) was seen in those species having higher water content. Since protein constitutes the major percentage of the AFDW (% DW), which is decreasing as water increases, the increase may be a relative one. A reduction in energy required for growth in deeper living species, achieved by reducing caloric content per unit weight as suggested by Childress and Nygaard, 1973, is supported by data for deeper living species investigated from the eastern Gulf of Mexico (Tables 2 and 3). A majority of the eastern Gulf species have reduced caloric content compared to those found in colder waters (Fig. 7). The reduced caloric content (primarily protein and lipid content) is probably not a buoyancy mechanism because it occurs in fishes with functional swimbladders as well as

PAGE 53

I 180 g 160 0 .... tO 140 0 ..... 120 z w 100 0 (J (J 80 -a: 0 ..J 60 < (J Fig. 7. \ \ \ \ \ \ \. \ \ \ \ \ \. \ \ \ \ CALIFORNIA CURRENT (BAILEY AND ROBISON). TRANSITION (CALIFORNIA CURRENT EASTERN N. PACIFIC GYRE). EASTERN NORTH PACIFIC GYRE. EASTERN GULF OF MEXICO. \ \ ' ', ....... ' ................ ........... --..... ..... ................... ......... ....... ..._ -...... ......... ..._ ...... ..... ... ..: ":1:11-. ------...... ---..... ........... ........,.__ ...... __ -.... .:::_7'.::.,::::_--------------. ..:.-------...._--200 400 600 800 1000 1200 MINIMUM DEPTH OF OCCURRENCE (m) Comparison of rigression curves of caloric content (Kcal 100 g ww-) on minimum depth of occurrence (MOO) in midwater fishes from: the California Current (Bailey and Robison, 1986, significant at P<0.05); transition between the California Current and the eastern N. Paci"fic gyre (Bailey and Robison, 1986, significant at P<0.05); the eastern N. Pacific gyre (Bailey and Robison, 1986, significant at P<0.05); the eastern Gulf of Mexico (Stickney, in prep., significant at P<0.01). 41

PAGE 54

42 those without (Childress and Nygaard, 1973). The higher caloric content in migrators than in non-migrators and weak migrators underscores the higher energy demands of the former group.

PAGE 55

4 3 CONCLUSIONS In conclusion, midwater fishes of the eastern Gulf of Mexico inhabit an area where many prey items are low in lipid content. Diets appear to be low in lipid content for several of the species studied. The center of night-time distribution for most fishes does not coincide with that of prey with the highest lipid content. The fact that prey items are low in lipid does not address the fact that lipids are not accumulated. The stable environment inhabited by these fishes p rovides a constant food supply, thereby reducing the need for lipid reserves. The other possibility is that energy requirements of entering the warm surface layers at night and living at high temperatures may preclude the possibility of lipid deposition due to high metabolic costs. The decrease in protein (% WW) with minimum depth of occurence supports previous studies demonstrating this trend. The generally higher protein values in migrators than in non-migrators and weak migrators, and relatively high skeletal ash in Gulf species supports the case for structural enhancement of fishes inhabiting an environment where there is a need for increased locomotory abilities. Further support for a positive correlation between protein

PAGE 56

44 content and the need for increased locomotion comes from a study of the eastern north Pacific gyre (Bailey and Robison, 1986) where the highest protein contents were found in individuals residing in areas of maximal light penetration and enhanced visual predation (Bailey and Robison, 1986). Food availability does not appear to correlate well with total protein content, rather the physiological demands associated with the need for increased locomotion appear to dictate the percentage of protein needed. The higher caloric content of the abundant migrators suggest their high energetic value in the eastern Gulf of Mexico where standing stocks are low.

PAGE 57

45 LITERATURE CITED Bailey, T.G: and B.H. Robison: Food availability as a select1ve factor on the chemical compositions of midwater fishes in the eastern North Pacific Mar. Biol.,91,131-141(1986) Barnett, M.A.: Species structure and temporal stability of mesopelagic fish assemblages in the Central Gyres of the North and South Pacific Ocean. Mar. Biol.,74, 245-256(1983) Blaxter, J.H.S., c.s. Wardle and B.L. Roberts: Aspects of the circulatory physiology and muscle systems of deepsea fish. J. Mar. biol. Ass. U.K.,51,991-10006,(1971) Bligh, E.G. and W.J. Dyer: A rapid method of total lipid extraction. Can. J. Biochem. Physiol.,37,911-917(1959) Brett, J.R. and T.D.D. Groves: Physiological energetics. In: Fish Physiology, Vol.VIII, pp 279-351. Ed. by W.S.Hoar and D.J.Randall. New York: Academic Press 1979 Brooks, A.L.: A study of the swimbladders of selected mesopelagic fish species. In: Oceanic sound scattering prediction. pp 565-590. Ed. by N.R. Anderson and B.J. Zahuranec. New York: Plenum Press 1977 Childress, J.J.: Physiological approaches to the biology of midwater organisms. In: Oceanic sound scattering prediction, pp 301-324. Ed. by N.R. Anderson and B.J. Zahuranec. New York: Plenum Press 1977 Childress, J.J. and M.H. Nygaard: chemical composition of midwater fishes as a funct1on of depth of occurrence off southern California. Deep-Sea Res.,20, 1093 -1109(1973) Childress, J.J. and M.H. Nygaard: Chemical and buoyancy of midwater crustaceans as a funct1on of depth of occurrence of occurrence off southern California. Mar.Biol.,76,165-177(1974)

PAGE 58

Childress, J.J. and M.H. Price: Growth rate of the bathPelagic crustacean Gnathophausia ingens Lophogastridae) 1. Dimensional growth and populat1on structure. Mar. Biol.,50,47-62(1978) Childress, .J:J. G.N. Somero: Depth related enzymic muscle, brain and heart of deep-living pelag1c mar1ne teleosts. Mar. Biol.,52,273-283(1979) Childress, J.J., S.M. Taylor, G.M. Caillet and M.H. Price: 46 Patterns of growth, energy utilization and reproduction in some meso-and bathypelagic fishes off southern California. Mar. Cullen, J.J., and R.W. Eppley: Chlorophyll maximum layers of the Southern California Bight and possible mechanisms of their formation and maintenance. Oceano!. 1,23-32(1981) Denton, E.J. and N.B. Marshall: The buoyancy of bathypelagic fishes without a gas-filled swimbladder. J. Mar. Biol. Ass. U.K.,37,753-767(1958) Dubois, M., K.A. Gilles, J.K. Hamilton, P.A. Rebers and F. Smith: Colorimetric method for determination of sugars and related substances. Analyt. Chem.,28, 350-356. Gartner, J.V., T.L. Hopkins, R.C. Baird and D.M. Milliken: The lanternfishes (Pisces: Myctophidae) of the eastern Gulf of Mexico. Fish. Bull.,85,81-98(1987) Hayward, T.L., and J.A. McGowan: Patt7rn and structure in an oceanic zooplankton commun1ty. Amer. Zool., 1045-1055(1979) Hopkins, T.L.: The vertical distribution of zooplankton in the eastern Gulf of Mexico. Deep Sea Res.,29,1069-1083 (1982) Hopkins, T.L. and R.C. Baird: Net feeding in mesopelagic fishes. Fish. Bull.,73,908-914(1975) Hopkins, T.L. and R.C. Baird: Aspects of feeding ecology of oceanic midwater fishes. In: Ocean1c sound scattering prediction, pp 325-360. Ed. by N.R. Anderson and B.J. zahuranec. New York: Plenum Press 1977 Hopkins, T.L. and R.C. Baird: Aspects of of the mesopelagic fish Lampanvctus Myctophidae) in the eastern Gulf of the trophic ecology alatus (Family Mexico. Biol.

PAGE 59

Hopkins, T.L. and R.C. Baird: Feeding of four hatchetfishes (Sternoptychidae) in the eastern Gulf of Mexico. Bull. Mar. Sci.,l2,260-277(1985) Hopkins, T.L., R.C. Baird and D.M. Milliken: A messengeroperated closing trawl. Limnol. oceanogr. 18 488-490 ( 1973) ,_, Keene, M.J., .R.H. and W.H. Krueger. Family Myctoph1dae, b1g scales. In: Biology of mid-water fishes.of the Bermuda Ocean acre. pp 169-185. Ed. by R.H. G1bbs and W.H. Krueger. Smithsonian contribution to zoology 1987 Lee, R.F., J. Hirota and A.M. Barnett: Distribution and importance of wax esters in marine copepods and other zooplankton. Deep-Sea Love, Malcolm: The chemical biology of fishes. pp 214-262. London, Academic press Inc., 1970 Lowrey, O.H., N.J.Rosebrough, A.L. Farrand R.R. Randall: Protein measurement with the folin phenol reagent. J. biol. Chem.,193,265-275(1951) Marsh, J.B. and D.B. Weinstein: Simple charring method for determination of lipids. J. Lipid Res.,2,574-576(1966) 47 Marshall, N.B.: swimbladder structure of deep-sea fishes in relation to their systematics and biology. Discovery Rep.,31,1-122(1960) McGowan, J.A.: The nature of oceanic ecosystems. In: The biology of the oceanic Pacific, pp 9-28. Ed. C.B. Miller. Oregon state Univ. Press 1974 McGowan J.A. and P.M. Williams: Oceanic habitat differences in the North Pacific. J. exp. mar. Biol. Ecol.,12,187-217(1973) Morris, M.J. and T.L. Hopkins: Biochemical composition of crustacean zooplankton from the eastern Gulf of Mexico. J. Exp. Mar. Biol. Ecol.,69,1-19(1983) Reinhardt, s.B. and E.S. Van Vleet: composition of twenty-two species of Antarct1c m1dwater zooplankton and fish. Mar. Biol.,jl,149-159(1986) Rohlf, F.J. and R.R. Sokal: Statistical tables, 253 pp. san Francisco: Freeman and Company 1969

PAGE 60

48 Sargent, J.R.: The structure, metabolism and function of lipids in marine organisms. In: Biochemical and biophysical perspectives in marine biology, pp 149-212. Ed. by D.C. Malina and J.R. Sargent. New York: Academic Press 1976 Torres, J.J., B.W. Belman and J.J. Childress:Oxygen consumption rates of midwater fishes as a function of depth of occurrence. Deep Sea Res.,26A,185-197(1979) Vinogradov, M.E. and V.B. Tseitlin: Deep-sea pelagic domain (aspects of bioenergetics). In: Deep-sea The sea, Vol.S, pp 123-165. Ed. by G.T. Rowe. New York: Wiley and Sons 1983


printinsert_linkshareget_appmore_horiz

Download Options

close
No images are available for this item.
Cite this item close

APA

Cras ut cursus ante, a fringilla nunc. Mauris lorem nunc, cursus sit amet enim ac, vehicula vestibulum mi. Mauris viverra nisl vel enim faucibus porta. Praesent sit amet ornare diam, non finibus nulla.

MLA

Cras efficitur magna et sapien varius, luctus ullamcorper dolor convallis. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Fusce sit amet justo ut erat laoreet congue sed a ante.

CHICAGO

Phasellus ornare in augue eu imperdiet. Donec malesuada sapien ante, at vehicula orci tempor molestie. Proin vitae urna elit. Pellentesque vitae nisi et diam euismod malesuada aliquet non erat.

WIKIPEDIA

Nunc fringilla dolor ut dictum placerat. Proin ac neque rutrum, consectetur ligula id, laoreet ligula. Nulla lorem massa, consectetur vitae consequat in, lobortis at dolor. Nunc sed leo odio.