The susceptibility of juvenile chinook salmon ( Oncorhynchus tshawytscha) to cataract formation in relation to dietary changes in early life

Abstract

A cataractogenic diet (C) and a control diet (A), containing high and low levels, respectively, of calcium, phosphorus and sodium phytate, were fed to juvenile chinook salmon in various sequences for three 42-day periods post swim-up. In addition, a diet (B), containing high levels of calcium and phosphorus but low sodium phytate, was fed for 126 days and in various sequences with diet A. All diets contained 0.06 g of zinc/kg dry diet. Cataracts were detected at day 126 in fish which were fed diet C between days 42 and 84. Fish growth was depressed severely by diet C and to a lesser extent by diet B. It is concluded that juvenile chinook salmon may be most prone to cataract formation between 42 and 84 days after swim-up. The results show that high dietary levels of calcium and phosphorus reduce smolt size and it is suggested that this may compromise marine survival.