ABSTRACT
Rainbow trout (Salmo gairdneri Richardson) with a body mass of 268 ± 36 g were used to determine the acceleration resistance of a fish during fast-starts. The mass of the fish was increased by mass loads of 75, 150, 225 and 335 g. The loads were made from nesting horseshoe-shaped brass saddles which fitted snugly over the fish so that the extra mass was equally distributed in all planes about the stretched-straight body centre of mass. The weight of the saddles was taken up by a 291 cm line attached to the dorsal surface of the fish above its centre of mass. The other end of the line was attached to the ceiling. The performance of the fish with and without saddles was measured during fast-starts, initiated by a 1 v.cm−1 d.c. electric shock. Performance was determined in terms of the distance travelled with time, measured from high speed movie films (240 frames s−1). The relationships between distance travelled and time were described by power functions for fish with and without mass loads. Exponents were not significantly different for the fish with various mass loads showing that frictional and form drag made negligible contributions to acceleration resistance in a fast-start. The resistance of the fish in a fast-start, due to fish mass and a resistance component of added water mass (apparent mass), was calculated using hydromechanical theory for representative fast-start sequences. The apparent mass was estimated at 320 g, which is 1·2 × fish body mass.
