ABSTRACT
This chapter deals with the contribution of the diet to osmoregulation of fish adapted to low salinities. Dietary salt supplementation can decrease energy spent on osmoregulation and consequently more will be available for growth. The absorption of dietary phosphorus is affected by the level of phosphate in the blood. Some studies proposed that acidic pH may impair growth in rainbow trout due to a decrease on food consumption, as was observed in silver catfish. Fish take up calcium for growth and homeostasis predominantly via the gills, directly from the water. In addition to being a major constituent of structural components of skeletal tissues, phosphorus is located in every cell of the body. Rainbow trout can survive for long fasting periods without a significant decrease on blood Na+ concentration. The proportion of chloride cells related to total branchial cells increased from 8% in rainbow trout fed with 1.3% dietary salt, to 10.5% in fish fed with 12% dietary NaCl.
