FISHERY BULLETIN: VOL. 80, NO. 4 



weight = 2.2 g) (Millikin in press and 1982, re- 

 spectively). In separate studies with rainbow 

 trout fingerlings, 35% dietary protein provided 

 as good a growth rate as 40 or 45% protein within 

 any of several temperature regimes (National 

 Research Council 1981). Fingerlings (mean ini- 

 tial weight = 2.0 g) fed either 35, 40, or 45% pro- 

 tein grew equally well within any one tempera- 

 ture regime (9°, 12°, 15°, and 18°C) over a 16-wk 

 period (Slinger et al. 1977, cited in National Re- 

 search Council 1981). Slightly larger rainbow 

 trout (mean initial weight = 3.45 g) also grew 

 equally well when fed 35, 40, or 45% dietary pro- 

 tein within any one of three temperature regimes 

 (9°, 12°, or 18°C) over a 24-wk period (Cho and 

 Slinger 1978, cited in National Research Council 

 1981). Growth rates were progressively higher at 

 each successive increase in rearing temperature, 

 regardless of dietary protein concentration, ex- 

 cept for 18°C in the second study. Increased feed 

 consumption of lower protein diets occurred 

 when rainbow trout were reared at higher tem- 

 peratures and probably satisfied higher protein 

 requirements at elevated water temperatures 

 (National Research Council 1981). Chinook salm- 

 on fry (0.4 g) require 53% dietary protein (dry 

 weight basis) combined with 16% dietary lipid 

 (dry weight basis) when reared at 5° or 12°C 

 based upon weight gain and survival rates (Fow- 

 ler 1980, 1981). However, growth rates were two 

 to three times more rapid for chinook salmon fry 

 reared at 12°C. 



Changes in salinity may alter protein require- 

 ments of anadromous or euryhaline species. Rain- 

 bow trout fingerlings require 45% protein for 

 optimal growth at 20%o compared with a 40% 

 protein requirement at 10%<> (Zeitoun etal. 1973). 

 Since a salinity of 10%ois almost isotonic with in- 

 ternal fluids (9% ) of rainbow trout fingerlings, 

 the higher dietary protein requirement for rain- 

 bow trout reared in a salinity of 20%c. suggests 

 that the higher dietary protein concentration 

 may assist in osmoregulation in a hypertonic ex- 

 ternal environment for this species (Zeitoun et al. 

 1973). Conversely, coho salmon, O. kisutch, smolts 

 require 40% protein in 10 and 20%«. Although 

 maximum weight gain occurred at 40% protein 

 in both salinities, maximum protein retention 

 occurred at 40% protein in 10%« and 50% protein 

 at 20%» (Zeitoun et al. 1974). The authors con- 

 cluded that the hyperosmotic environment (20 %<>) 

 did not stress coho salmon smolts in the same 

 manner as previously shown with smaller rain- 

 bow trout fingerlings. Also, underyearling rain- 



bow trout (mean weight = 70 g) require more 

 dietary arginine (1.2% of the diet) when reared in 

 freshwater than in those individuals reared in 

 20%o (1.0% arginine of the diet) (Kaushik 1977, 

 cited in Poston 1978). Further work is necessary 

 to more firmly establish whether protein require- 

 ments change with salinity for specific life stages 

 of various anadromous or catadromous fish spe- 

 cies. 



AMINO ACIDS 



Qualitative and Quantitative Requirements 



Examination of qualitative amino acid require- 

 ments of fishes has often been based upon growth 

 and feed efficiency in long-term feeding studies. 

 Typically, one of several amino acids is removed 

 singly from a well-defined formula diet which is 

 assumed to be nutritionally complete (i.e., posi- 

 tive control), to determine if significant reduc- 

 tion in weight gain occurs in fish fed the selected, 

 amino acid-deficient diets compared with growth 

 of fish fed the control diet. Thereafter, any group 

 of fish fed a diet determined to be deficient in an 

 amino acid, as indicated by reduced growth and 

 feed efficiency, is separated into two subgroups: 

 One subgroup is retained on the amino acid-defi- 

 cient diet (control diet minus one amino acid), 

 whereas the other subgroup is fed the control 

 diet. Reduced growth rate or cessation of growth 

 in fish fed the amino acid-deficient test diet ver- 

 sus the control diet is considered to be confirma- 

 tion of a dietary requirement for the specific 

 amino acid being tested. On the basis of such 

 amino acid feeding studies, several fish species 

 have been found to require the same 10 amino 

 acids (arginine, histidine, isoleucine, leucine, 

 lysine, methionine, phenylalanine, threonine, 

 tryptophan, and valine) as essential dietary con- 

 stituents. Species requiring dietary inclusion of 

 these amino acids include chinook salmon (Hal- 

 ver et al. 1957); rainbow trout (Shanks et al. 

 1962); sockeye salmon, O. nerka (Halver and 

 Shanks 1960); channel catfish (Dupree and Hal- 

 ver 1970); Japanese eel, Anguilla japonica, and 

 European eel, Anguilla anguilla (Arai et al. 

 1972b); common carp (Nose et al. 1974); red sea 

 bream, Chryxophrys major (Yone 1975); and red- 

 belly tilapia, Tilapia zilli (Mazid et al. 1978). 



Qualitative amino acid requirements of plaice, 

 Pleuronectes platessa, and sole, Solea solea, were 

 investigated, using intraperitoneal injections of 

 uniformly labelled - 14 C-glucose into individuals 



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