Hydrobiologia 358: 265–268, 1997. 265A. Hagiwara, T. W. Snell, E. Lubzens & C. S. Tamaru (eds), Live Food in Marine Larviculture.c 1997Kluwer Academic Publishers. Printed in Belgium.

Essential fatty acid profiles of maturation feeds used in freshwaterornamental fish culture

Clyde S. Tamaru1, Harry Ako2 & Restituto Paguirigan21SeaGrant Extension Service, School of Ocean Earth Science and Technology, Aquaculture DevelopmentProgram, Department of Land and Natural Resources, 1000 Pope Road, MSB 226 Honolulu, Hawaii 96822, USA2College of Tropical Agriculture and Human Resources, Department of Environmental Biochemistry, Henke Hall,329 Honolulu, Hawaii 96822, USA

Key words:essential fatty acids, maturation, freshwater, ornamental fish

Abstract

An investigation of live or freshly prepared feeds used as ‘maturation’ diets for freshwater ornamental fish wasconducted to uncover similarities or differences in total and essential fatty acids. Analysis of these ‘maturation’feeds reveals that there are relatively low levels of total fatty acids (0.81–8.96 mg/100 mg�1 dry weight) and withthe exception of the beef heart diet all other feeds have undetectable levels of docosahexaenoate (22:6n3). Thebeef heart diet was observed to possess 4.86 mg 100 mg�1 dry weight of 22:6n3 most probably due to the additionof skipjack tuna,Katsuwanus pelamis, roe. All other feeds examined were found to contain low to moderatelevels of eicosapentaenoate (20:5n3) 0.00–0.61 mg/100 mg�1 dry weight. Surprisingly relatively high amounts ofarachidonate (20:4n6) 0.16–0.90 mg/100 mg�1 dry weight were observed in all of the maturation diets and rangedbetween 3.79%–27.16% on a percent composition basis. The results obtained to date indicate a need to scrutinizethe role of arachidonate in the maturation and spawning process.

Introduction

A major finding during the development of hatcherytechnologies for marine teleosts was the understand-ing of the nutritional requirements, at all stages in thelife history of fishes, and the effects that result fromfailing to meet those requirements (Watanabe et al.,1983; 1984). Preliminary investigations, in Hawaii, ongrowout of angelfish,Pterophyllum scalare, and gold-fish,Carassius auratus, using feeds developed for theculture of carnivorous marine fish species have resultedin significant improvements in growth and cost savingsfor their culture (Ako, et al., in prep). The results wereencouraging enough to pursue examining the effectsof commercially prepared feeds designed for use withmarine fish species on maturation and spawning offreshwater ornamental species. The first stage in theinvestigation was to examine the total and essentialfatty acids of current feeds used for maturation of fresh-water ornamental fishes.

Materials and methods

Source and preparation of feeds

Live earthworms and mosquito larvae were obtainedfrom a compost bin and bucket of rainwater, respec-tively, located in Maunawili, Hawaii USA. Daphniawas obtained from Lance Pang of Wainani Kai, Hon-olulu, Hawaii, USA. The beef heart preparation andblack tubifex worms were obtained from Fred Lum ofPacific Discus Hatchery, Honolulu, Hawaii USA. Redtubifex worms were obtained from Patrick Vahey ofHanohano Enterprises, Punaluu, Hawaii, USA. All liveand prepared feeds were collected, rinsed in freshwa-ter and stored frozen at�20�C until analyzed. Resultsobtained for beef liver are from a previous investigation(Iwai et al., 1992). Fatty acid analysis was conductedas summarized in Tamaru et al. (1992). The values pre-sented are the averages from triplicate determinations

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and unless specified otherwise, are expressed in termsof mg/100 mg�1 dry weight.

Results

Essential fatty acid profiles of maturation feeds

A summary of the total and essential fatty acids foundin the various feeds used for the maturation and spawn-ing of freshwater ornamental fishes is presented inTable 1. Total fatty acids were observed to rangebetween a low of 0.81 found in earthworms to a highof 8.95 found in beef liver. With the exception of thebeef heart preparation all other feeds were found tobe deficient in 22:6n3. All feeds contained 20:5n3 thatranged between a low of 0.07 found in daphnia to ahigh of 0.61 found in the black tubifex worms. Rel-atively high levels of 20:4n6 were observed in all ofthe feeds tested ranging between a low of 0.16 foundin daphnia to a high of 0.90 found in black tubifexworms. Both 18:3n3 and 18:2n6 were found to rangebetween 0.00–0.51 (beef liver – black tubifex worms)and 0.11–1.71 (earthworms and daphnia – beef heartdiet), respectively.

The data of the observed essential fatty acids weresummarized in a non-conventional fashion (i.e. percentcomposition) where each of the essential fatty acidswithin a particular feed was divided by the observedtotal fatty acids in the respective feed. The value wasthen multiplied by 100. Each of the essential fatty acidswere then ranked on the basis of the percent compo-sition of total fatty acids as summarized in Table 2.When the data are presented in this fashion, all feedsexhibit a high percent composition of either 18:2n6 or20:4n6. On a percent composition basis 18:2n6 rangedfrom a low of 2.61% found in daphnia to a high of35.19% found in the beef heart diet. On a percent com-position basis 20:4n6 was found to range from a lowof 3.42% found in daphnia to a high of 27.16% foundin earthworms.

Discussion

The various live feeds and fresh feed preparationsexamined during the current study are invariably usedby freshwater ornamental fish breeders, who fromexperience have found them to be effective in bringingabout maturation and spawning of their target species.It is interesting to note the inclusion of skipjack tuna

roe in the beef heart diet prepared for growth andmaturation of discus,Symphysodon discus. Discus-sion with numerous freshwater ornamental fish breed-ers reveals similar inclusions of marine products (e.g.blood worms, fish roe, squid, crustacean meat) with apreparation of beef heart or beef liver. While inclusionof marine products in freshly prepared diets is beingpracticed, many hobbyists rely solely on the other livefeeds currently being investigated. The results indicatethat these feed items do not have detectable levels of22:6n3. In addition, the live feeds examined possessrelatively low levels of 20:5n3. This would lead oneto hypothesize that a large number of freshwater orna-mental fishes do not require the long chain polyunsatu-rated fatty acids as has been reported to be essential formarine fish species (Watanabe et al., 1983, 1984). Both18:2n6 and 20:4n6 were found to be the major essentialfatty acids present in the live feeds investigated in thecurrent study implying that they play a critical role inreproduction as these feeds are religiously used by thehobbyist/breeder of ornamental freshwater fishes. Ithas been reported that juvenile chinook salmon do notexhibit the ability to convert dietary 18:2n6 to 20:4n6(Dosanjh et al., 1988) and it remains to be demonstrat-ed to what extent the conversion of 18:2n6 to 20:4n6takes place in teleosts. If this situation is pervasive infreshwater teleosts, then it is not surprising that 20:4n6is present in large quantities in the prey items that thefish consume.

The relatively high levels of both 18:2n6 and 20:4n6in the feeds investigated in the current study are consis-tent with their reported biological roles. In higher ver-tebrates, metabolic conversion of 18:2n6 is the sourceof 20:4n6 (Galli, 1980; Kinsella, 1987) and 20:4n6has been identified as the precursor for prostaglandins(Kinsella, 1987). Prostaglandins have been demon-strated to play a critical role during the ovulatoryprocess in teleosts or serving as pheromones that stim-ulate mating behavior in fishes synchronizing both thephysiological and physical components of the spawn-ing event between both sexes (Goetz, 1983; Kobayashiet al., 1986; Stacey et al., 1986). Investigations into thefatty acid profiles of spawned eggs from striped mul-let, Mugil cephalus, maturing under natural and arti-ficial conditions suggest a linkage with the observedlow levels of 20:4n6 detected in spawned eggs and thereproductive process (i.e. lower percent fertilization)observed in striped mullet (Tamaru et al., 1992). Thedata on the essential fatty acids observed in the variouslive feeds and prepared diets presented in the currentinvestigation strongly suggests that 20:4n6 plays an

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Table 1. Essential fatty acids of maturation feeds used for freshwater ornamental fishes. Valuesare reported in mg 100 mg�1 dry weight.

Fatty acid Beef Beef Black Red Daphnia Earth Mosquito

heart liver Tubifex Tubifex worms larvae

diet worms worms

18:2n6 1.71 1.56 1.68 1.43 0.11 0.11 0.48

18:3n3 0.20 0.00 0.51 0.19 0.04 0.10 0.31

20:4n6 0.51 0.22 0.90 0.64 0.16 0.22 0.33

20:5n3 0.11 0.00 0.61 0.33 0.07 0.09 0.23

22:6n3 0.33 0.00 0.00 0.00 0.00 0.00 0.00

Total fatty acids 4.86 8.96 6.22 4.68 4.22 0.81 8.27

Table 2. Summary of essential fatty acids found in maturation feeds ranked by percentcomposition.

Ranking Beef Beef Black Red Daphnia Earth Mosquito

heart liver Tubifex Tubifex worms larvae

diet worms worms

1 18:2n6 18:2n6 18:2n6 18:2n6 20:4n6 20:4n6 18:2n6

2 20:4n6 20:4n6 20:4n6 20:4n6 18:2n6 18:2n6 20:4n6

3 22:6n3 18:3n3 20:5n3 20:5n3 20:5n3 18:3n3 18:3n3

4 18:3n3 20:5n3 18:3n3 18:3n3 18:3n3 20:5n3 20:5n3

5 20:5n3 22:6n3 22:6n3 22:6n3 22:6n3 22:6n3 22:6n3

integral part in the reproductive mechanism of a largenumber of freshwater ornamental fishes. A concert-ed effort needs to be initiated to determine what thefunction of 20:4n6 is in the reproductive processes ofteleosts.

Acknowledgments

Partial funding was provided by a grant from theNational Oceanic and Atmospheric Administration,project #A/AS-1 sponsored by the University ofHawaii Sea Grant College Program, InstitutionalGrant No. NA36RG0507, Department of Commerce,UNIHI-SEAGRANT-TR-96-01. The views expressedherein are those of the authors and do not necessarilyreflect the views of NOAA or any of its sub-agencies.Support for the project was also provided by the Aqua-culture Development Program, Department of Landand Natural Resources, State of Hawaii, as part oftheir Aquaculture Extension Project with University ofHawaii Sea Grant Extension, Service Contract #9638.The authors wish to thank Christine Carlstrom-Trickof Hawaii C’s Aquaculture Consultant Services for hereditorial comments.

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