Biostatistical implications of individual variability in growth in rainbowtrout and Atlantic salmon

The relationship between specific growth rate and initial body weight in fi sh was analysed by multivariate analysis using data sets from growth studie s on rainbow trout (initial weight between 10 and 30 g, n = 546) and Atlant ic salmon (initial weight between 10 and 20 g, n = 355). We demonstrate tha t individuals can be pooled into different classes according to their growt h characteristics. Classes with similar initial mean weight can have very d ifferent mean specific growth rate. Indeed, we found the mean specific grow th rate ratio between classes with similar initial mean weight to be betwee n 1.5 and 5.8 in rainbow trout and between 1.2 and 1.9 in Atlantic salmon. We conclude that the constitution of replicates with homogeneous initial we ight is not assurance of homogeneous specific growth rate among replicates. The consequences of such variability in growth on experimental designs and power of analysis-of-variance models are discussed. (C) 2001 Elsevier Scie nce B.V. All rights reserved.