A STUDY OF FERAL CARP, CYPRINUS-CARPIO L, EXPOSED TO MICROCYSTIS-AERUGINOSA AT LAKE-MOKOAN, AUSTRALIA, AND POSSIBLE IMPLICATIONS FOR FISH HEALTH

Feral carp, Cyprinus carpio L., were collected at bimonthly intervals for 12 months from Lake Wellington, where there was no evidence of sig nificant growth of Microcystis aeruginosa. Various blood parameters of these carp were measured to ascertain the normal range values for fer al carp in this region. A similar study was conducted at Lake Mokoan, where M. aeruginosa formed a visible scum that contained detectable le vels of microcystins for 4 consecutive months. Carp were taken from La ke Mokoan each month, and the histology and blood biochemistry of the fish were examined for indications of microcystin toxicity. During Feb ruary, March and April, 66% of the carp from Lake Mokoan had livers wi th widespread hepatocyte atrophy, and 37% of the fish had gills with p inpoint necrosis, epithelial ballooning, folded lamellar tips and exfo liation of the lamellar epithelium. Compared to carp from Lake Welling ton, the serum aspartate aminotransferase activity and the serum bilir ubin concentrations of carp from Lake Mokoan were elevated during Janu ary, February, March and April. The data were consistent with impaired hepatocyte function in some carp from Lake Mokoan. Serum sodium and c hloride concentrations in carp from Lake Mokoan were lower than those for carp at Lake Wellington from December to April, indicating that mo st carp from Lake Mokoan had difficulty maintaining cation-anion homeo stasis during this period. Nevertheless, carp at Lake Mokoan always ap peared healthy, and no mortalities were reported.