Measuring fish condition: an evaluation of new and old metrics for three species with contrasting life histories

Abstract

Measuring fish condition should link ecosystem drivers with population dynamics, if the underlying physiological basis for variations in condition indices are understood. We evaluated traditional (K, Kn, hepatosomatic index, gonadosomatic index, energy density, and percent dry weight of muscle (%DWM) and liver (%DWL)) and newer (bioelectrical impedance analysis (BIA) and scaled mass index (SMI)) condition indices to track seasonal cycles in three flatfishes — winter founder (Pseudopleuronectes americanus; three stocks), yellowtail flounder (Limanda ferruginea; three stocks), and summer flounder (Paralichthys dentatus; one stock) — with contrasting life histories in habitat, feeding, and reproduction. The %DWM and %DWL were good proxies for energy density (r2 > 0.96) and more strongly related to K, Kn, and SMI than to BIA metrics. Principal component analysis indicated many metrics performed similarly across species; some were confounded by size, sex, and maturity along PC1, while others effectively characterized condition along PC2. Stock differences were along PC1 in winter flounder, reflecting different sizes across stocks, whereas in yellowtail flounder differences occurred along PC2 related to condition. These comparisons, within and across species, highlight the broad applicability of some metrics and limitations in others.

Growth, condition, and swimming performance of juvenile Pacific herring with winter feeding rations

“…Given the strong influence of lipid and moisture in the LDA, their utility for distinguishing poorly fed and well-fed wild herring appears similar to that of the LDA functions, and their biological interpretation is more straightforward. Lipid and moisture were strongly inversely related, as has been reported elsewhere across several species (Anthony et al 2000;Wuenschel et al 2019), indicating that either variable alone may be adequate for distinguishing wild fish. If the results had indicated instead that several measured variables made similar contributions to the LDA functions, thus making the effect of any specific variable ambiguous, then applying LDA functions derived from lab fish could be especially useful for assessing wild herring with measurements on those variables.…”

Primary production and depth drive different trophic structure and functioning of fish assemblages in French marine ecosystems

“…Changes in energy density of forage species can dramatically impact the population dynamics of marine top predators, and can be explained by a change in energy density of their preys (Österblom et al 2008;Spitz et al, 2012;Trites & Donnelly, 2003). In addition with stable isotopes and species biomass, energy density is a pertinent indicator of fish condition, and of the quality of matter fluxes, particularly for lipid transfer from zooplankton to fish (Saraux et al, 2019;Spitz et al, 2010 and references therein;Van Beveren et al, 2014;Wuenschel et al 2019).…”

Resource partitioning across a trophic gradient between a freshwater fish and an intraguild exotic

“…Body condition was evaluated with relative weight (Wege & Anderson, 1978; Wuenschel et al., 2018) and compared by area and season using separate ANOVA for each species (Bister et al., 2000; Blackwell et al., 2003; Liao et al., 2001). Assumptions for the ANOVAs were tested with Levene's (for normality) and the Shapiro–Wilk (for variance homogeneity) statistics (Zar, 1999).…”