FISHERY BULLETIN: VOL. 80, NO. 4 



concentrations fed to coho salmon fingerlings re- 

 sulted in reduced growth rate and feed efficiency 

 values (Yu and Sinnhuber 1979). On the other 

 hand, rainbow trout fingerlings had best growth 

 rates and feed efficiency when fed higher trilino- 

 lenin concentrations combined with low trilino- 

 lein concentrations (5% trilinolenin plus 0% trili- 

 nolein or 3% trilinolenin plus 1% trilinolein) (Yu 

 and Sinnhuber 1976). In a separate study, rain- 

 bow trout fingerlings fed a diet sufficient in 18: 

 3cu3 (1% ethyl linolenate) actually had better 

 growth rates and feed efficiency than fish fed 1% 

 ethyl linolenate plus 1.5% ethyl linoleate (Yu and 

 Sinnhuber 1975). Dietary supplements of 5% 

 ethyl linoleate to feeds containing 0.1, 0.5, or 

 1% ethyl linolenate markedly reduced growth 

 and feed efficiency of rainbow trout finger- 

 lings. 



Chum salmon, 0. keta, fed 5% dietary lipid as 

 either 5% methyl laurate, 4% methyl laurate plus 

 1% 18:2oj6, 4% methyl laurate plus 1% 18:3o>3, or 

 3% methyl laurate plus 1% 18:2o>6 and 1% 18:3to3, 

 showed best weight gain and feed efficiency 

 when offered the 3% methyl laurate plus simul- 

 taneous supplements of 1% 18:2cu6 and 1% 18:3o»3 

 (Takeuchi et al. 1979). Also, simultaneous sup- 

 plementation of 18:2w6 (1%) and 18:3o;3 (1%) pro- 

 duced slightly better weight gain of chum salmon 

 fingerlings than 4% methyl laurate plus 1% of a 

 highly unsaturated fatty acid mix (containing 

 26.5% 20:5a>3 plus 42.1% 22:6a>3). However, mini- 

 mal dietary requirements of 18:2a;6 or 18:3a>3for 

 optimal growth rate of chum salmon fingerlings 

 were not determined. 



Dietary supplements of either methyl linoleate 

 or methyl linolenate at 0.5 or 1.0% concentrations 

 provided better growth of Japanese eel finger- 

 lings than a fat-free diet or 7% methyl laurate (T. 

 Takeuchi et al. 1980). However, contradictory 

 results in two separate studies by these investi- 

 gators prevent any conclusions regarding mini- 

 mal requirements of 18:2oj6 and 18:3co3 for this 

 species. 



Common carp fry and fingerlings have demon- 

 strated better growth when fed diets containing 

 highly polyunsaturated fats (e.g., cod liver oil) 

 than those containing 5% methyl laurate (Wata- 

 nabe 1975a, b). Intermediate growth rates oc- 

 curred in common carp fry fed either 1% methyl 

 linoleate or 1% methyl linolenate plus 4% methyl 

 laurate over a 22-wk period (Watanabe et al. 

 1975a), whereas 1% methyl linoleate or 1% methyl 

 linolenate did not improve growth of common 

 carp fingerlings over an 18-wk period (Wata- 



nabe et al. 1975b). 



High variability exists among various fish spe- 

 cies in ability to elongate and desaturate dietary 

 18-carbon fatty acids to 20- or 22-carbon fatty 

 acids. Several marine species appear to have 

 lower enzymatic elongation-desaturation capa- 

 bilities than freshwater fishes. Administration 

 of (1 — 14 C) 18:3a>3 to individuals of red sea 

 bream; black sea bream, Mylio macrocephalus; 

 opaleye, Girella nigricans; striped mullet, Mugil 

 cephalus; and rainbow trout indicated that only 

 rainbow trout exhibited appreciable radioactiv- 

 ity in 22:6c«3 of body lipids (Yamada et al. 1980). 

 Therefore, it was concluded that marine species 

 have limited ability to elongate and desaturate 

 18:3w3, resulting in dietary essentiality of eico- 

 sapentaenoic acid (20:5a>3) or 22:6a>3 and non- 

 essentiality of 18:3oj3. In another study, injec- 

 tions of (1 — 14 C) 18:3(o3 into two individuals 

 of each of several fish species resulted in inten- 

 sive incorporation of 18:3o>3 into 20:5ai3 and 22: 

 6cu3 in rainbow trout, while very low percent 

 bioconversion of 18:3<w3 to 20:5a»3 and 22:6cu3 

 occurred in marine fish such as globefish, Fugu 

 rubripes rubripes; Japanese eel; red sea bream; 

 rockfish, Sebasticus marmoratus; and ayu, Pleco- 

 glossus altivelis (Kanazawa et al. 1979). The re- 

 sults of this study confirmed that pathways of 

 elongation and desaturation of dietary 18-carbon 

 fatty acids are poorly developed in marine fishes 

 compared with rainbow trout. Earlier, Castell et 

 al. (1972c) had reported elevated 20:4w6 and 22: 

 5w6 concentrations in body lipids of rainbow 

 trout fed 1% 18:2a>6 as well as elevated 22:6^3 

 concentrations in individuals fed 1% 18:3a;3, sug- 

 gesting an ability of rainbow trout to elongate 

 and desaturate linoleic and linolenic acid. Also, 

 rainbow trout, fed a fat-free diet or 5% oleic acid 

 (18:1oj9) as the sole dietary lipid, accumulated 

 high body lipid concentrations of eicosatrienoic 

 acid (20:3w9), an indicator of essential fatty acid 

 deficiency in terrestrial animals. Furthermore, 

 comparison of dietary fatty acid composition and 

 initial and final body fatty acid composition of 

 rainbow trout in another feeding study, suggests 

 the ability of this species to elongate and desatu- 

 rate 20:5tu3 into 22:6a»3 (Castledine and Buckley 

 1980). Cowey et al. (1976) concluded thatturbot 

 lack the necessary microsomal desaturases to 

 effectively convert 18:lcu9, 18:2co6, or 18:3oj3 into 

 polyunsaturated fatty acids for deposition in 

 neutral fats or phospholipids based upon growth 

 and body lipid composition. Also, 1% dietary 18: 

 3w3 or 1% arachidonic acid (20:4<u6) in the pres- 



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