Dynamics of nest defense by male centrarchid fish.

Field observations were conducted on four species of nesting male centrarchids to determine if guarding males discriminate intruders with respect to their potential threat to the brood, their size or position in the water column, or by the stage of the nest. Results demonstrated that bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) sunfish were the most frequent intruders and were attacked the most often. Nest guarding male largemouth bass (Micropterus salmoides) attacked intruders further from the nest and had the highest probability of attack of the four species studied. Rock bass (Ambloplites rupestris) males had the shortest distance of attack and one of the lowest probabilities of attack. Male black crappie (Pomoxis nigromaculatus) and pumpkinseed were intermediate in both responses. For all species, the size of intruder did not influence attack distance but larger males had a greater attack distance than smaller males. The distance of attack was greatest during the period immediately after hatch. These findings indicate species-specific differences in nest defense and males did discriminate intruders, possibly on their potential threat to the brood. The defense of the nest was related to nest stage, a finding which supports current theory of parental care.