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