THE EFFECTS OF SMALL-SCALE TURBULENCE ON THE INGESTION RATE OF FATHEAD MINNOW (PIMEPHALES-PROMELAS) LARVAE

Small-scale turbulence increases encounter rates between planktonic pr edators and their prey. It has been hypothesized to lead to an increas e in feeding by fish larvae, yet this has rarely been tested experimen tally. We investigated the effects of turbulence on feeding by fathead minnow (Pimephales promelas) larvae to test the null hypothesis of no effect of turbulence on ingestion. In one experiment, larvae were exp osed to four turbulent velocities from 0 to 2 cm . s(-1) at a single p rey concentration. Data analysis led to a rejection of the null hypoth esis. Moreover these data suggested a significant nonlinear response o f ingestion to increasing turbulence. In a second experiment, we varie d turbulence and prey concentrations (15, 50, and 500 prey/L) simultan eously. We rejected the null hypothesis of no effect of turbulence for all prey concentrations. Results differed among prey concentrations. We observed a negative linear response for the two lower prey concentr ations, but a domed response at 500 prey/L. We conclude that turbulenc e does influence ingestion, but not as suggested by an extension of en counter models. Thus, turbulence may not always be beneficial in the f ield.