reductions in weight gain occurred in channel 

 catfish fed diets containing 17.5 or 33.5 mg cop- 

 per/kg dry diet compared with those individuals 

 fed 9.5 mg copper/kg dry diet. Also, a slight re- 

 duction occurred in the number of erythrocytes 

 and hematocrit levels in channel catfish fed 33.5 

 mg copper/kg dry diet resulting in slight anemia. 

 Murai et al. (1981) suggested that since fish can 

 absorb copper from the surrounding water, ab- 

 sorption of environmental copper may result in 

 lower dietary copper requirements than that re- 

 quired by most terrestrial animals. Common 

 carp fingerlings fed 0.7 mg copper/kg dry diet 

 had lower weight gain than individuals fed 3.0 

 mg copper/kg dry diet (Ogino and Yang 1980). 

 In contrast, no differential growth response oc- 

 curred in rainbow trout fingerlings fed either 0.7 

 or 3.0 mg copper/kg dry diet (Ogino and Yang 

 1980). 



Selenium 



Selenium is an essential dietary constituent for 

 Atlantic salmon and rainbow trout. Poston etal. 

 (1976) demonstrated dietary essentiality of sele- 

 nium for Atlantic salmon fry and fingerlings. 

 Deficiency of dietary selenium suppressed gluta- 

 thione peroxidase activity, while supplements of 

 both vitamin E (500 IU DL-a-tocopheryl acetate/ 

 kg) and selenium (0.1 mg/kg dry diet) prevented 

 muscular dystrophy. However, no minimal die- 

 tary selenium requirement nor minimal seleni- 

 um concentration causing toxicity was deter- 

 mined for Atlantic salmon. Dietary selenium 

 concentrations as low as 0.07 mg/kg dry diet pre- 

 vented selenium deficiency symptoms (i.e., de- 

 generation of liver and muscle) in rainbow trout 

 fingerlings concurrently fed 400 IU vitamin E/ 

 kg dry diet while reared in water containing 0.4 

 isg selenium/1 (Hilton etal. 1980). Since selenium 

 is a component of glutathione peroxidase, it is of 

 interest that maximal plasma glutathione per- 

 oxidase activity was obtained at a dietary sele- 

 nium concentration of 0.15 to 0.38 mg/kg dry 

 feed. On the other hand, selenium toxicity oc- 

 curred in rainbow trout fed dietary selenium 

 concentrations of 13 mg/kg of dry diet, causing 

 reduced growth and feed efficiency and uncoordi- 

 nated spiral swimming behavior 12 to 24 h be- 

 fore death. Hilton et al. (1980) emphasized the 

 importance of reporting dietary vitamin E con- 

 centrations and water borne selenium concen- 

 trations when investigating dietary selenium re- 

 quirements of fish. 



FISHERY BULLETIN: VOL. 80, NO. 4 



Iodine 



Iodine has been shown to have a role in thyroid 

 metabolism in fishes similar to that occurring in 

 terrestrial animals. Woodall and LaRoche(1964) 

 examined dietary iodide requirements of chinook 

 salmon fed 0.1 to 10.1 mg iodide/kg diet during 

 an initial 6-mo study and an additional 9-mo 

 study. After 6 mo, no significant differences oc- 

 curred in growth, feed efficiency, and body com- 

 position. However, iodine stored in the thyroid 

 glands of chinook salmon fed 0.1 mg iodide/kg 

 dry diet equaled only 40% of the iodide in indi- 

 viduals fed higher iodide concentrations (0.6, 1.1, 

 5.1, and 10.1 mg iodide/kg dry diet). The authors 

 concluded that the minimal dietary iodide re- 

 quirement of chinook salmon fingerlings was 

 about 0.6 mg iodide/kg dry diet based upon the 

 iodide content in thyroid glands. Additionally, 

 they recommended a higher dietary iodide re- 

 quirement for advanced parr (1.1 mg iodide/kg 

 dry diet) and speculated that smoltification may 

 be accompanied by increased thyroid activity. 

 Increased thyroid activity has been demon- 

 strated in several salmonids during the parr- 

 smolt transformation (Wedemeyer et al. 

 1980). 



SUMMARY AND 

 RECOMMENDATIONS 



1) All fish species examined thus far in feeding 

 studies require the same dietary essential 

 amino acids (arginine, histidine, isoleucine, 

 leucine, lysine, methionine, phenylalanine, 

 threonine, tryptophan, and valine). 



2) Optimal dietary lipid concentrations for 

 maximal protein sparing action in most 

 fish species range from 12 to 24%. 



3) Qualitative essential fatty acid require- 

 ments and ability to elongate and desatu- 

 rate fatty acids such as linoleic and linolenic 

 acids are highly variable among fishes, in- 

 dicating a need for more species-specific 

 research. 



4) Relative protein sparing action of carbo- 

 hydrates and lipids is also highly variable 

 among fish species, necessitating more spe- 

 cies-specific research in place of approxi- 

 mating metabolic capabilities of an un- 

 studied species based upon knowledge of 

 other species. 



5) Extensive research is needed to determine 



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