Domoic acid in rainbow trout ( Oncorhynchus mykiss) feeds

Contamination of fish feeds with the toxin, domoic acid, through use of contaminated fish meal is a possibility. To test the stability of domoic acid during fish meal and fish feed manufacturing, fish meal was made from anchovies containing 43 μg domoic acid/g wet fish using a closed vacuum dryer, resulting in fish meal containing 130 μg domoic acid/g of meal. This product was used in place of commercial herring meal in a dry, pelleted feed, constituting 50% of the feed formulation. The feed contained 58 μg domoic acid/g. To determine if dietary domoic acid affected the health of rainbow trout or was retained in the tissue, duplicate groups of trout, average initial weight 25 g, were fed a control diet, made with herring meal, and the domoic acid diet for 15 weeks, during which time the average weight of the trout increased to 48 g. No differences in feed consumption, weight gain, or feed efficiency ratio were observed between groups of fish fed the control or domoic acid feed. No mortality or signs of toxicity or neurological distress were observed in either dietary treatment group. Analysis of fish tissue showed no detectable concentrations of domoic acid in fillets or viscera portions of the fish when the fish were sampled after a 48-h fast. Domoic acid was present in the feces and viscera, but not in blood or muscle of the fish following an overnight fast. These results suggest that domoic acid in fish feed, when present at a concentration likely to be encountered in practical situations, is not readily absorbed by rainbow trout and does not present a health hazard to the fish or to the consumer.