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.