MILLIKIN: NUTRIENT REQUIREMENTS OF FISHES 



any) dietary magnesium requirements, since 12 

 versus 66 mg magnesium/ 100 g diet fed to red 

 sea bream did not differentially affect growth, 

 vertebral magnesium content, or vertebral cal- 

 cium content. 



Quantitative dietary magnesium requirements 

 for rainbow trout (0.06 to 0.07%) and carp (0.04 to 

 0.05%) were established based upon one dietary 

 calcium concentration and one calcium and mag- 

 nesium concentration in ambient water in each 

 study (Ogino et al. 1978; Ogino and Chiou 1976, 

 respectively). Cowey (1976) reported that exces- 

 sive dietary calcium (2.7%) in relation to dietary 

 magnesium (0.04%) was accompanied by renal 

 nephrocalcinosis in rainbow trout, while 0.1% 

 magnesium fed to rainbow trout along with 2.7% 

 calcium resulted in normal renal calcium con- 

 centrations. Further increases in dietary cal- 

 cium concentrations to 4% required dietary mag- 

 nesium concentrations of 0.1%, rather than 0.06% 

 magnesium to prevent renal calcinosis (Cowey et 

 al. 1977). Therefore a direct interrelationship 

 was established between dietary calcium and 

 magnesium fed to rainbow trout in freshwater 

 (Cowey 1976). 



bow trout fed 1 mg zinc/kg dry diet (Ogino and 

 Yang 1978). Although carboxypeptidase activity 

 was not tested, lower activity of this zinc-contain- 

 ing enzyme could explain lower protein digesti- 

 bility (Ogino and Yang 1978). Ketola (1979b) 

 determined that laboratory diets containing 40% 

 white fish meal (60 mg zinc/kg dry diet) caused 

 bilateral cataracts in rainbow trout, possibly as a 

 result of excesses of other minerals in white fish 

 meal (calcium, phosphorus, sodium, or potas- 

 sium). Supplementation of 150 mg zinc/kg dry 

 diet to the laboratory diet containing 40% white 

 fish meal and 60 mg zinc/kg dry diet resulted in 

 normal growth rates and prevented cataract for- 

 mation in rainbow trout. Common carp, fed 1 

 ppm dietary zinc in the presence of 10 jug zinc/1 

 rearing water over 12- and 16-wk periods in sep- 

 arate studies, had high mortality rates, reduced 

 growth rate, and had fin and skin erosion (Ogino 

 and Yang 1979). No cataract formations were re- 

 ported in zinc deficient common carp, however. 

 Common carp fingerlings required between 15 

 and 30 ppm of dietary zinc for optimal growth. 



Iron 



Manganese 



Common carp and rainbow trout fingerlings 

 have been found to have higher growth rates 

 when fed 12 to 13 mg manganese/kg dry diet ver- 

 sus 4 mg manganese/kg dry diet (Ogino and 

 Yang 1980). Manganese-deficient rainbow trout 

 displayed abnormal curvature of the backbone 

 and malformation of the tail. 



Zinc 



Zinc has been shown to be an essential trace 

 element for rainbow trout in separate studies 

 (Ogino and Yang 1978; Ketola 1979b) and com- 

 mon carp (Ogino and Yang 1979). Dietary zinc 

 concentrations of 15 and 30 mg/kg dry diet fed 

 over an 8-wk period in the presence of 1 1 ;ug zinc/1 

 of rearing water promoted satisfactory growth 

 of rainbow trout, while 5 mg zinc/kg dry diet 

 produced slightly slower growth rates (Ogino 

 and Yang 1978). In the same study, rainbow 

 trout fingerlings fed 1 mg zinc/kg dry diet had 

 poor growth, high mortality (46% vs. 0% in other 

 treatments), high incidence of cataracts (49% vs. 

 0% in other treatments) and high incidence of fin 

 erosion (86% vs. 0% in other treatments). Protein 

 digestibility was appreciably reduced in rain- 



Dietary iron is essential for fishes to maintain 

 normal hemoglobin content, hematocrit value, 

 and mean corpuscular diameter. Hypochromic, 

 microcytic anemia occurred in red sea bream 

 (Yone 1975) and common carp (Sakamoto and 

 Yone 1978b) as well as anisocytosis in red sea 

 bream fed iron-deficient diets. Control diets fed 

 to red sea bream and common carp, which pre- 

 vented these iron deficiency symptoms, contained 

 1.2 g ferric citrate/kg dry diet and 199 mg iron/ 

 kg dry diet, respectively. A minimal dietary iron 

 concentration of 150 mg/kg diet is required to 

 prevent iron deficiency symptoms such as low 

 mean corpuscular diameter and low blood iron 

 content in red sea bream (Sakamoto and Yone 

 1978a). 



Copper 



Dietary copper requirements have been inves- 

 tigated for channel catfish, common carp, and 

 rainbow trout. Copper requirements, if any, for 

 fingerling channel catfish are <1.5 mg/kg dry 

 diet (Murai et al. 1981). Channel catfish fed 9.5 

 mg copper/kg dry diet while reared in water con- 

 taining 0.33 ng copper/1 for 16 wk grew signifi- 

 cantly slower than individuals fed diets contain- 

 ing only 3.5 mg copper/kg dry diet. Further 



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