Temporal Spawning Distribution of Largemouth Bass and Young-of-Year Growth, Determined from Daily Otolith Rings

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Abstract
Age and growth of young-of-year largemouth bass M. salmoides in Lake Shelbyville, Illinois [USA] were determined from daily growth rings in otoliths of fish collected in Sept. of 1980 and 1981. Otolith ages, adjusted for the interval from spawning to the start of feeding (swim-up), revealed that spawning of largemouth bass occurred during 45 days from late April until early June in both years. Spawning occurred at temperatures of 12-20.degree. C. In mid-Sept., 60-75% of the variation in largemouth bass lenghts was attributable to age. Older individuals had increased their initial length advantage through faster average daily growth. Back-calculated lengths at 5 day intervals indicated that growth was most rapid to early Aug. and had decreased by mid-Sept. Growth of individuals that reached swim-up in mid-June declined much more rapidly than growth of individuals that reached swim-up in late May. Differences in growth between largemouth bass that reached swim-up on different dates were associated with differences in their ability to make the transition from an invertebrate to a fish diet. If overwinter survival depends upon length attained during the first growing season, temporal spawning distribution may be an important factor affecting year-class strength.

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