The reproductive cycle of yellow bass, Morone mississippiensis, in Clear Lake, Iowa

Abstract

Gillnet collections of yellow bass, Morone mississippiensis, were made from April, 1967 to September, 1968 at Clear Lake, Iowa to determine the normal reproductive cycle and variations in fecundity which could be related to changes in food supply and water temperatures. A major mortal­ ity from Aeromonas infection occurred in May, 1968 which also allowed documentation of changes in body condition, fecundity and success of reproduction during the year preceding a mass mortality from disease. Spawning was initiated during mid-May in 1967 and late April in 1968 when water temperatures approached 15°C after a rapid temperature rise of 3.5 to 4.5°C over several days. At spawning time ovaries of adult bass comprised up to 16 percent body weight and testes up to 8 percent body weight. Fish commenced spawning when maturing ova reached a mean diameter of 0.4 mm in the preserved state. Fresh ovulated ova averaged 0.8 + 0.11 mm in diameter. Wide variation in effective fecundity was apparent among mature females of similar length. Although 50 percent of the variation in fecundity could be attributed to body length in 1967, the relation was not significant in 1968 (r = 0.32). In 1967 mature females contained an average of 560 mature ova per mm total body length in contrast to 276 ova in 1968. In terms of body weight the average female produced 835 ova per gram body weight in 1967 but only 350 in 1968. The change in fecundity was attributed to poor body condition in 1968. Females measuring 200 mm total body length weighed approximately 137 grams in 1967 at spawning time but only 115 grams in 1968.