Effect of Substrate Composition and Stock Origin on the Survival to Emergence of Brown Trout: A Laboratory Study

Few researchers investigating the survival to emergence of embryonic salmonids have simultaneously compared the predictive ability of the percentage of fine sediment less than a given diameter, the geometric mean particle size, and the fredle index. We quantified the relation between these different measures of suhstrate compoaition and survival to emergence of two stocks of brown trout, Salmo crutta, and also rxamincd the effects of sutlstrate composition on the timing of emcrgcnce and size of alevins. The geometric mean particle size generally accounted for the greatest proportion of variation in survival to emergence, whereas the percentage of fines less than a given size was usually the poorest predictor. Substrate composition also influenced days to first emergence and 50% emergence and the length of the emergence interval. We found no difference in the survival to emergence of the two stocks. We concluded that the geometric mean particle size was the best predictor of survival to emergence for brown trout and that substrate rornpo.sihn may alter other ecological characteristics of emerging fry.