THE EFFECT OF THE ISOPOD PARASITE CERATOTHOA-GAUDICHAUDII ON THE BODY-WEIGHT OF FARMED SALMO-SALAR IN SOUTHERN CHILE

A study of the isopod Ceratothoa gaudichaudii, a parasite on farmed At lantic salmon was carried out on Guar island, Chile, between May 1993 and August 1994. A total of 671 salmon, with an initial body weight of 0.9 kg to 1.1 kg, was selected; one third were naturally infected wit h one or two growing parasites. The fish were kept in a separate cage and were examined individually, under anaesthesia, five times during t he study. On each occasion, the weight and number of the parasites on each fish was recorded. There was an increase in the prevalence of the parasitosis from 33.4% to 98.2%; concurrently, the total number of pa rasites on salmon rose from 309 to 3987 with an increase of infestatio n intensity from 1.4 to 6.1 parasites per fish. No adult females with eggs or larvae were found. At the end of the study, salmon with less t han three parasites weighed 4428 +/- 949 g; those with three to eight parasites weighed 4151 +/- 983 g, and those with more than eight paras ites weighed 3763 +/- 1056 g. A significant difference in weight (P < 0.05) among the three groups was detected.