EFFECTIVENESS OF IVERMECTIN ON THE ECTOPA RASITE CALIGUS SP IN FARMEDTROUT (ONCORHYNCHUS-MYKISS) IN THE SOUTH OF CHILE

In order to gather information on the parasitosis caused by the copepo d Caligus sp. on O. mykiss and to test two Ivermectin treatment regime s, a study was carried out in a trout farm located on Quinchao Island, Chiloe, Xth Region, Chile. Ivermectin was incorporated to the food to reach a total dose of 0.15 mg/kg per fish and was administered in two different regimes to eight cages with 10,000 trout each: in Regime 1 the drug was provided to the trout of four cages 3 times (at 6 day int ervals) in doses of 0.05 mg/kg; in Regime 2 the product was supplied t o the trout of another four cages 5 times (at 3 day intervals) at a do se of 0.03 mg/kg. Two cages were maintained without treatment as contr ol. Fish from each cage were sampled before the treatment and five tim es (at weekly intervals) after the treatment to count the copepodes. T he chalimus and adult parasites were preferently located on the fish's surface. The fish with higher intensity of infestation showed cutaneo us lesions and cornea opacity. Both regimes reduced (p<0.05) chalimus and adult parasites in comparison to the control group. No significant difference between the two treatments was found.