Effects of prey type on motor pattern variance in tetraodontiform fishes

It is unclear whether the high variance of electromyographic parameters mea sured in feeding teleost fishes reflects functionally significant motor var iation that is under control of the fish, or functionally insignificant var iation characteristic of EMG data. We addressed this issue by examining the effect of three prey, differing in physical characteristics, on the feedin g motor pattern in three fishes of the Order Tetraodontiformes: the filefis h, Monacanthus hispidus; the triggerfish, Balistes capriscus; and the puffe r, Sphoeroides nephelus. EMG recordings were made from subdivisions of the mouth closing adductor mandibulae muscle and the mouth opening levator oper culi muscle in four fish from each species feeding on live fiddler crabs, l ive shrimp, and pieces of cut squid mantle. Analysis of variance was used t o test for effects of prey type on the standard deviation of muscle burst d uration, burst onset time, and average burst amplitude in the adductor musc les. The filefish exhibited a doubling of standard deviation of burst durat ion in all muscles when feeding on fiddler crabs; triggerfish showed increa sed standard deviations in onset times and duration of two muscles when fee ding on squid mantle; and the puffer showed no effects of prey on motor var iability. The observation that prey type can elicit more than a doubling in the standard deviation of some EMG traits indicates that a large portion o f the within-prey type variance is under direct control of the individual f ish, suggesting an even greater level of fine motor control in teleost feed ing mechanisms than previously recognized. J. Exp. Zool. 286:563-571, 2000. (C) 2000 Wiley-Liss, Inc.