Integral projection model reveals differences in individual growth performance and body mass distributions in response to three different rations in a large aquaculture experiment

Fed aquaculture is one of the fastest growing and most valuable food production industries. The efficiency with which farmed fish convert feed into biomass influences both environmental impact and economic revenue. Salmonid species, such as king salmon (Oncorhynchus tshawytscha), exhibit high levels of plasticity in vital rates such as feed intake and growth rates. Accurate estimations of individual variability in vital rates are important for production management. The use of mean trait values to evaluate feeding and growth performance can mask individual-level differences that potentially contribute to inefficiencies. Here, we apply an integral projection model (IPM) to investigate individual variation in growth performance of 1625 individually tagged king salmon fed one of three distinct rations and tracked over 276 days. To capture the observed sigmoidal growth, we compared a non-linear mixed-effects (logistic) model to a linear regression model used within the IPM framework. Ration significantly influenced several aspects of growth. Mean final body mass and mean growth rate increased with ration, however, variance in body mass and feed intake also increased significantly over time. Trends in body mass mean and variance were captured by both logistic and linear models, suggesting the linear model to be suitable for use in the IPM. Higher rations resulted in a decreasing proportion of individuals reaching the cohort’s mean size or larger by the end of the experiment. This suggests that, in our trial, feeding to satiation did not produce the desired effects of efficient and uniform growth in juvenile king salmon. While monitoring individuals through time is challenging in commercial aquaculture settings, recent technological advances combined with an IPM approach could provide new scope for tracking growth performance in experimental and farmed populations. The IPM framework also allows the exploration of other size-dependent processes affecting vital rate functions, such as competition and mortality.