IMMUNOCHEMICAL METHOD AS EARLY DIAGNOSIS FOR DISTINGUISHING SALMONID FISH FEMALE AND MALE PRIOR TO GENITAL MATURATION BY USE OF A MINUTE AMOUNT OF BLOOD COLLECTED FROM A SINGLE PIECE OF GILL FILAMENT

Immunochemical methods to distinguish female and male salmonid fish pr ior to genital maturation with anti-vitellogenin (Vg) antibody have be en developed. Diluted plasma of each fish was subjected to enzyme-link ed immunosorbent assay (ELISA) using rabbit antiserum raised against V g purified from the plasma of estradiol-injected male Oncorhynchus myk iss (rainbow trout) and the sex was tested with 100% accuracy in June, 4 months before spawning. Even in April or May, the method was applie d with 80% accuracy. The present method required less than 2-3 mul of the blood sample, which we collected by picking up a piece of gill fil ament from individual fish and placing it in phosphate-buffered saline . By employing a dot-blotting method of ELISA on a polysulfone membran e, the test was completed in about 4 hours. The present method using a nti-rainbow trout Vg can be used for other fish whose Vg cross-reacted with this antibody, for example, Oncorhynchus masou (yamame in Japane se) and Salvelinus leucomaenis pluvius (iwana in Japanese).