FISHERY BULLETIN: VOL. 80. NO. 4 



1981). Results generally suggested that reason- 

 able agreement occurs between average appar- 

 ent amino acid availability and protein digesti- 

 bility values of any one specific protein source. 

 However, individual amino acid availabilities 

 were quite variable within and among various 

 feed ingredients tested. Also, apparent amino 

 acid availability values were considerably less 

 than true amino acid availability values for feed 

 ingredients containing relatively low protein 

 content (e.g., 9 to 19%), such as rice bran, rice mill 

 feed, wheat middlings, and corn. 



Lysine 



Dietary lysine requirements for fishes range 

 from 5.0 to 6.8% of the dietary protein. In addi- 

 tion to the quantitative lysine requirements listed 

 in Table 3, rainbow trout fry require 6.8% lysine 

 and lake trout, Salvelinus namaycush, fry re- 

 quire 6.0% lysine as a percentage of total dietary 

 protein (Ketola 1980). Robinson et al. (1980b) re- 

 ported a dietary lysine requirement of 5% of the 

 dietary protein for channel catfish fed an ade- 

 quate dietary protein concentration (30%); thus 

 confirming a dietary lysine requirement (5.1% of 

 the dietary protein) for channel catfish fed a 

 marginal dietary protein concentration of 24% 

 (Wilson et al. 1977). Excessive dietary lysine in 

 the presence of marginal or adequate dietary 

 arginine concentrations did not depress growth 

 or feed efficiency of channel catfish, nor did ex- 

 cessive arginine depress growth or feed efficien- 

 cy of channel catfish in the presence of marginal 

 dietary lysine concentrations (Robinson et al. 

 1981). This is in contrast to lysine-arginine an- 

 tagonisms reported for several terrestrial spe- 

 cies (Maynard and Loosli 1969). 



Lysine deficiency in fish may conceivably re- 

 sult in depressed rates of collagen formation. 

 Hydroxylysine has been shown to be a constituent 

 of collagen in several fish species (Mehrle 5 ). Fin 

 rot occurred in rainbow trout fed a lysine-defi- 

 cient diet containing corn gluten meal as the sole 

 protein source (Ketola 1979a). Supplementation 

 of a combination of lysine, arginine, histidine, 

 isoleucine, threonine, tryptophan, and valine to 

 the corn gluten meal diet resulted in improved 

 survival, increased growth, and prevention of 

 severe caudal fin erosion. At the same time, 



5 Paul M. Mehrle, Columbia National Fisheries Research 

 Laboratory, U.S. Fish and Wildlife Service, Columbia, MO 

 65201, pers. commun. December 1981. 



removal of lysine from the amino acid mixture 

 in the corn gluten meal supplemented diet in- 

 creased mortality, reduced growth, and resulted 

 in caudal fin erosion of rainbow trout. 



Methionine 



Quantitative dietary methionine requirements 

 for several fish species have been shown to de- 

 pend upon dietary cystine concentration, since 

 cystine can substitute for a portion of the methi- 

 onine requirement. This is the result of the con- 

 version of methionine to cystine being a common 

 pathway of intermediary metabolism in many 

 terrestrial animals (Maynard and Loosli 1969) as 

 well as fish (National Research Council 1973). 

 Rainbow trout fingerlings require 0.6% methio- 

 nine (1.7% of the dietary protein) and 0.45% cys- 

 tine (1.29% of the dietary protein), a total sulfur 

 amino acid requirement of 1.05% of the diet 

 (2.99% of dietary protein). This is based upon 

 growth and feed efficiency as demonstrated by 

 feeding studies, using a factorial design of 0.3 to 

 0.75% methionine and 0.04 to 0.6% cystine (Page 

 1978). Excessive cystine for rainbow trout (e.g., 

 0.6%) did not partially satisfy methionine re- 

 quirements in methionine-deficient diets (0.3 and 

 0.45% methionine) based on weight gain and feed 

 conversion. Chinook salmon require 0.5 to 0.6% 

 dietary methionine (1.3 to 1.5% of the dietary pro- 

 tein) in the presence of 1.0% dietary cystine, 

 whereas 1.6% methionine did not produce maxi- 

 mum growth in the presence of 0.05% dietary 

 cystine (Halver et al. 1959). Channel catfish re- 

 quire 0.56% dietary methionine (2.34% of the die- 

 tary protein) in the absence of cystine, while 60% 

 of the methionine requirement is replaceable 

 with cystine (Harding et al. 1977). 



Methionine deficiency has been shown to re- 

 sult in cataractogenesis in lake trout fingerlings 

 and rainbow trout fingerlings. After 12 wk, rain- 

 bow trout fingerlings (initial mean weight = 1.5 

 g) fed 0.6% methionine plus 0.3 or 0.45% cystine 

 did not develop any cataracts (Page 1978). Lower 

 dietary methionine content (0.3 or 0.45%) com- 

 bined with dietary cystine content ranging from 

 0.04 to 0.6% produced varying degrees of cata- 

 racts in rainbow trout. In another study, lake 

 trout fingerlings were fed methionine-deficient 

 diets (0.36% methionine = 0.96% of the dietary 

 protein) containing soybean protein isolate as 

 the sole protein source (40% of the diet). After 

 8 wk, lake trout fingerlings showed only initial 

 signs of opacification of subcapsular areas (Pos- 



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