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As per Tracy's request - some parts of a study.
Behavioral Suppression of Spawning in Largemouth Bass by Interspecific Competition for Space Within Spawning Areas STEPHEN LEE SMITH Florida Game and Fresh Water Fish Commission Eustis, Florida 32726
ABSTRACT Florida largemouth bass ,Micropterus salmoides florldanus, fail to spawn in association with Dense populations of stunted sunfish. A recent study indicated that a "physical factor" rather than a chemical factor may be responsible. Three hatchery ponds containing marked bass were stocked at different points in the bass Reproductive cycle with concentrations of sunfish known to suppress spawning. It was determined that reduced or complete inhibition of spawning of largemouth bass is related to interspecific population densities in the spawning area and is behavioral in nature. Suppression is linked to aggressive interaction with other species ,primarily affects the male bass, and is effective in suppressing the spawning behavior sequence even before nest construction.
As early as 1964 it was noted that Florida Largemouth bass , , failed to produce a year class in several eutrophic Florida lakes with large populations of sunfishes (Lepomis spp.) (Horel 1964). Chew (1972) further documented this phenomenon and determined that reproductive failure was due to "a refusal of the adult population to spawn" and was characterized in the female by the "retention of enlarged, ripened ovaries long past the spawning period." He found that the condition could be reproduced in hatchery ponds and attributed reproductive inhibition to the "excretion and build-up of a hormone-like repressive factor by overcrowded bream and forage species Other workers have reported the failure of largemouth bass to spawn in the presence of large numbers of sunfish and concluded that failure was due to either sunfish predation on the eggs (Swingle and Smith 1943) or to a repressive factor excreted by sunfishes which inhibited spawning (Swingle 1956; Chew 1974). Barwick and Holcomb (1976) were the first to indicate that some other factor may be responsible. By segregation of bass and sunfish while allowing free flow of water between areas they obtained successful bass reproduction and concluded that suppression of spawning was probably not due to a chemical substance excreted into the water. It was postulated that "lack of reproduction was apparently associated with a physical factor that in some way interrupted normal bass breeding activity." The study reported here was an attempt to determine the nature of this "physical factor" and the point in the reproductive cycle at which it is effective.
The observations reported here indicate that reduced or complete inhibition of spawning of largemouth bass is linked to aggressive interaction with other species primarily affects the male bass, and is effective in suppressing the spawning behavior sequence even before nest building.
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