Deficiency symptoms of calcium have not been described in fish although poor growth is observed with diets limited in phosphorus (which leads to reduced accretion of calcium by body tissues). Prolonged feeding of phosphorus-deficient diets to common carps resulted in deformed backs (lordosis) and heads due to abnormal calcification of bone. Bone growth was reduced in the skull and operculum regions. Recent studies with this species and the red sea bream have also shown fatty infiltration of liver and muscle tissues related to dietary phosphorus deficiency.
Calcium and Phosphorus in Feeds
Feed ingredients vary widely in their calcium and phosphorus content. Fish meal, a principal ingredient in fish feeds, is rich in both calcium and phosphorus. On the other hand, feed ingredients of plant origin usually lack calcium and, despite a fairly high content of phosphorus the latter is predominantly in the form of phytin or phytic acid which is not readily available for absorption by fish. Animal sources of calcium and phosphorus are generally better absorbed, although the stomachless carp cannot utilize bone phosphate present in fish meal as well as fish with functional stomachs. Dicalcium phosphate has the highest availability (80 percent). Phosphorus availability of common feedstuffs varies from 33 percent for grains to 50 percent for fish meal and animal by-products. Soybean meal has an intermediate phosphorus availability of 40 percent.