ABSTRACT
Fast-start kinematics and performance were determined for Etheostoma caeruleum, Cottus cognatus, Notropis cornutus, Lepomis macrochirus, Perca flavescens, Salmo gairdneri and a hybrid Esox sp. at an acclimation and test temperature of 15 °C. Normal three-stage kinematic patterns were observed for all species. Fast-start movements were similar in all species, except Lepomis, which had slightly higher amplitudes than expected for its length. The duration of kinematic stages was a major variable among the seven species but was a linear function of length. Acceleration rates were not functions of size. Maximum acceleration rates ranged from 22·7 to 39·5 m. s−2 with mean rates from 6·1 to 12·3 m.s−2, averaged to the completion of kinematic stage 2. Maximum velocity and distance covered in each fast-start stage varied among species but were related to length. Fast-start performance depended primarily on compromise between muscle mass as a percentage of body mass, and lateral body and fin profile. Optimal profiles provide large depth distant from the centre of mass to maximize thrust, and anterior depth enhancement to minimize recoil. The body form of Lepomis is considered optimal for multiple swimming modes.
This convention has been routinely used by Weihs (1973) and Webb (1975a, 1976, 1977) in discussing fast-start mechanics, as described in those papers. A different convention has been adopted in studies on neurological factors involved in fast-starts (e.g. Eaton et al. 1977) : responses are measured for the rostral tip of the head. The measurements of the rostral tip of the head include the net motion of the fish (as measured by the motion of the centre of mass) plus motions associated with lateral propulsive movements. These are large in kinematic stage 1 compared to the movements of the centre of mass (Weihs, 1973 ; Webb, 1975a). Later in a fast-start, the path of the centre of mass and the rostral tip of the head begin to overlap. Then kinematics and mechanics approach steady swimming patterns and the forward motion of the two motions are sufficiently similar that they can be interchanged. It is important to note that the various performance measures derived from the two conventions, associated with different lines of inquiry, are not intended to be equivalent, and cannot be equated.
