Body and Fin Form and Strike Tactics of Four Teleost Predators Attacking Fathead Minnow (Pimephales promelas) Prey

Abstract

Experiments with teleosts attacking fathead minnow (Pimephales promelas) prey showed that piscivore locomotor tactics vary with body/fin morphology. Predators were tiger musky (Esox sp.), rainbow trout (Salmo gairdneri), smallmouth bass (Micropterus dolomieui), and rock bass (Ambloplites rupestris) representing several morphological series from more flexible to more rigid bodies, elongate to gibbose bodies, soft-rayed to acanthopterygian median/paired fin patterns, and more to less myotomal muscle. Two predicted optimal tactics were common to the four predators: (1) strike at the prey center of mass and (2) strike prey from the side. Other tactics varied among the predators. Tiger musky always used S-start fast-starts, rainbow trout used steady swimming with body/caudal fin movements, and smallmouth and rock bass used steady swimming with body/caudal fin movements for closer prey and started attacks on distant prey with pectoral propulsion. Tiger musky overshot prey, this being prevented by the use of paired fins as brakes in the two centrarchids. Rainbow trout regularly chased prey, but effective braking coupled with suction feeding appeared to make chases less necessary for smallmouth and rock bass. Speeds in strikes increased according to rock bass < smallmouth bass < rainbow trout < tiger musky consistent with expectations based on morphology. Each species used attack speeds likely to minimize closure times, which is the general optimal strategy for interceptors. Tiger musky attacked at maximum speeds but rainbow trout and smallmouth and rock bass attacked at speeds very much lower than their maximum potential. The prey has a low response threshold for these three species compared with tiger musky when high speeds and associated large prey reaction distances would increase closure times.