Spawning Period and First-Year Growth of Northern, Florida, and Intergrade Stocks of Largemouth Bass

Abstract Subspecific differences in spawning period and first-year growth of largemouth bass Micropterus salmoides were investigated by examination of otoliths from experimental populations established in research ponds in Illinois. Compared with Florida largemouth bass M. s. floridanus, northern largemouth bass M. s. salmoides were spawned earlier and grew larger (total length, weight) during the first growing season. Intergrade fish exhibited characteristics of age and growth intermediate between those of the two pure parental subspecies. The observed differences in size were independent of age, indicating that first-year differences in size were enhanced by genetic differences affecting growth rate. Peak production of F1 intergrades occurred during the overlap in the northern and Florida largemouth bass spawning periods. However, F1 intergrades were produced throughout the overall period of largemouth bass spawning.