SIZE-DEPENDENT AND SPECIES-DEPENDENT VARIABILITY IN CONSUMPTION AND GROWTH-RATES OF LARVAE AND JUVENILES OF 3 FRESH-WATER FISHES

We tested the hypothesis of no species differences in consumption and growth rates using three species of Lake Michigan fish (yellow perch ( Perca flavescens), bloater (Coregonus hoyi), and alewife (Alosa pseudo harengus)), that hatch over a wide range of sizes (3.5-9.5 mm). ingest ion and growth rates were significantly different among the three spec ies for 10- and 20-mm fish, although differences were weaker for 10-mm growth rates. Incorporating these consumption and growth rate estimat es and their parameter errors into a simulation model revealed that di fferences among species in survival could be detected with as few as 3 samples (model runs) for 20-mm fish at both low and high prey density and for 10-mm fish at low prey density, but that 23 samples would be required to detect differences for 10-mm fish at high prey density. Co mpared with our 8-h estimates, previous short-term (15-30 min) consump tion rate estimates for the same three species overestimated consumpti on rates for the 20-mm fish but underestimated them for the 10-mm fish . Our results suggest that differences in growth and ingestion among t he three species are likely even when fish are 10 mm, but that we may not always be able to detect differences in survival of smaller fish.