Chronic toxicity of dietary disodium arsenate heptahydrate to juvenile rainbow trout (Oncorhynchus mykiss).

Juvenile rainbow trout were fed semi-purified diets containing graded levels of disodium arsenate heptahydrate (DSA) for 12-24 weeks under standard laboratory conditions to define the maximum acceptable toxicant concentration (MATC) and to correlate signs of toxicity with diet and tissue arsenic concentrations. The MATC for DSA was between 13 and 33 micrograms As/g diet or 0.281-0.525 mg As/kg body weight/day. The most sensitive and reliable indicator of chronic dietary DSA toxicity in rainbow trout was chronic inflammation of the gallbladder wall. Chronic inflammatory changes in the sub-epithelial tissues of the gallbladder wall were evident in 71% of rainbow trout exposed to 33 micrograms As/g diet for 24 weeks, and 100% of rainbow trout exposed to 65 micrograms As/g diet for 24 weeks or 49 micrograms As/g diet for 12 weeks. No fish exposed to 13 micrograms As/g diet or less for up to 24 weeks showed any demonstrable gallbladder lesions or any other ill effect of arsenic exposure. Other signs of chronic dietary DSA toxicity to rainbow trout included decreased growth rate, mild to moderate anemia, and, at higher levels of exposure, active feed refusal leading to decreased feed consumption. Mild nephrocalcinosis was noted in one experiment where kidney arsenic residues exceeded 14 micrograms As/g tissue dry weight.