FISHERY BULLETIN: VOL. 80, NO. 4 



up to 1.2 mg menadione sodium bisulfite/kg dry 

 diet. 



MINERALS 



Calcium and 

 Calcium-to-Phosphorus Ratios 



Initial investigations indicated that calcium 

 uptake in fish is primarily through imbibition 

 and gill absorption rather than from dietary 

 sources (Podoliak 1961; Simmons 1971). Never- 

 theless, since calcium and phosphorus are both 

 major components of fish bone and scales, die- 

 tary calcium-to-phosphorus ratios were exam- 

 ined by several investigators to determine if any 

 interactions occur between calcium and phos- 

 phorus, which might result in altered bone ash, 

 calcium, and phosphorus content. Dietary cal- 

 cium did not affect growth and feed efficiency of 

 common carp (Ogino and Takeda 1976), channel 

 catfish (Lovell 1977), and rainbow trout (Ogino 

 and Takeda 1978). However, in a separate study 

 with channel catfish, 1.5% dietary calcium in- 

 duced maximal weight gain, whereas lower and 

 higher dietary calcium concentrations produced 

 less weight gain (Andrews et al. 1973). Optimal 

 growth and feed conversion occurred in channel 

 catfish fingerlings fed a 1.5:1 ratio of calcium to 

 phosphorus (Andrews et al. 1973) and optimal 

 feed efficiency and serum inorganic phosphorus 

 were observed in red sea bream fed a 1:2 ratio 

 of calcium to phosphorus (Sakamoto and Yone 

 1973). The difficulty in determining whether die- 

 tary calcium-to-phosphorus ratios are nutrition- 

 ally significant in fish may be complicated by 

 dietary factors such as magnesium and vitamin 

 D or use of suboptimal calcium water concentra- 

 tions in various studies. Based on the few species 

 studied, it is unknown whether salinity deter- 

 mines if dietary calcium-to-phosphorus ratios 

 are important dietary factors. Optimal dietary 

 calcium-to-phosphorus ratios have been reported 

 for one marine species (red sea bream) and one 

 freshwater species (channel catfish), while no 

 optimal ratios were reported for common carp or 

 rainbow trout. 



Phosphorus 



Dietary essentiality of phosphorus has been 

 verified for channel catfish (Andrews et al. 1973; 

 Lovell 1978), Atlantic salmon (Ketola 1975a), red 



sea bream (Yone 1975), common carp (Ogino and 

 Takeda 1976), and rainbow trout (Ogino and 

 Takeda 1978). Deficiency symptoms in channel 

 catfish include reduced growth, poor feed effi- 

 ciency, low bone ash, and low hematocrit levels 

 (Andrews et al. 1973), and reduced weight gain, 

 bone ash, and bone phosphorus content (Lovell 

 1978). Red sea bream fed phosphorus-deficient 

 diets contained lower vertebral ash, calcium, 

 and phosphorus and more brittle bone structure 

 (Yone 1975). Common carp and rainbow trout 

 fed diets deficient in phosphorus had reduced 

 calcium, phosphorus, and ash content of whole 

 body and vertebrae (Ogino and Takeda 1976; 

 Ogino and Takeda 1978, respectively). Also, 

 Ogino and Takeda (1976) reported deformity of 

 the frontal bone of the cranium of common carp 

 and spondylolisthesis, brachyospondylie, and 

 synostosis of vertebrae in phosphorus-deficient 

 individuals. 



Based on examination of limited sources of 

 phosphorus, dietary phosphorus requirements 

 have been reported as 0.4% or 0.42 to 0.47% for 

 channel catfish (Gatlin et al. 1982; Lovell 1978, 

 respectively), 0.6% inorganic phosphorus supple- 

 mented to a diet containing 0.7% phosphorus 

 from plant sources for Atlantic salmon (Ketola 

 1975a), 0.68% for red sea bream (Yone 1975), 

 0.6 to 0.7% for common carp (Ogino and Takeda 

 1976), and 0.7 to 0.8% for rainbow trout (Ogino 

 and Takeda 1978). Supplementation of 0.4 to 2% 

 monosodium, monocalcium, or dicalcium phos- 

 phate to diets containing 0.55 to 0.65% available 

 phosphorus did not improve growth or feed effi- 

 ciency of rainbow trout fingerlings (initial mean 

 weight = 21 g) over an 18-wk period (Reinitz et 

 al. 1978a). Generally, inorganic phosphorus in 

 formulated feeds is more digestible or available 

 for fishes than organic forms of phosphorus 

 occurring in soybean meal and fish meal (Ketola 

 1975a, b; Lovell 1978). 



Magnesium 



Magnesium is an essential constituent of bone 

 in fish and is interrelated with calcium metab- 

 olism. Whole body and vertebral calcium content 

 were inversely related to dietary magnesium 

 concentration in common carp (Ogino and Chiou 

 1976) and rainbow trout (Ogino et al. 1978), 

 whereas whole body and vertebral phosphorus 

 content were unaffected by dietary magnesium 

 in the same species. Sakamoto and Yone (1979) 

 concluded that marine fishes have very low (if 



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