Energy allocation in juveniles of a warm-temperate reef fish

Abstract

During the first year of life, organisms are faced with competing demands for energy between growth and storage. Most research on energy allocation in young fishes has focused on cold-temperate species which are subjected to strong seasonal fluctuations in productivity, while few studies have considered those at lower latitudes where seasonality is less pronounced. Gag (Mycteroperca microlepis) of the northeastern Gulf of Mexico settle in coastal seagrass beds in the spring as juveniles and emigrate to offshore reefs in the fall. Upon settlement, these young fish grow at remarkably fast rates, but their growth slows considerably before emigration. Slowed growth can be explained by one of three hypotheses:(1) size-specific emigration times; (2) reduced feeding efficiency associated with declines in primary and secondary productivity; or (3) energetic shifts in allocation from growth to storage. Gag emigrate essentially as a cohort, so slowed growth does not result from differential emigration patterns based on fish size. They also emigrate before seasonal declines in primary and secondary productivity; thus, food remains abundant and feeding efficiency constant. The more plausible hypothesis is that there is an energetic shift from growth to storage. The liver serves as the primary site of lipid storage and the hepatosomatic index of juvenile gag increases coincident with reduced growth. The overall effect of increased energy stores is presumably for use during offshore migration and/or for overwinter survival.

Growth, energy storage, and feeding patterns reveal winter mortality risks for juvenile Pacific herring in Prince William Sound, Alaska, USA

“…RNA/DNA and lipid data were transformed (natural log and square root, respectively) to meet regression assumptions of normally distributed residuals and equal variances. A piecewise regression approach was used because we expected the energy allocation strategy could shift at a fixed length for juvenile herring, as has been observed for other juvenile fishes in seasonal environments (Post & Parkinson 2001, Stallings et al 2010). In addition, exploratory analysis of November data using generalized additive models (GAMs; Wood 2006) suggested that the slopes of the relationships between RNA/DNA or % lipid and length were not linear and changed abruptly at intermediate lengths.…”

Regime shifts shorten food chains for mesopredators with potential sublethal effects

“…Total lipid content and lipid class composition of muscle, liver and gonad tissues were analysed to measure the allocation of energetic reserves to growth, storage and reproduction respectively (Stallings, Coleman, Koenig, & Markiewicz, 2010;Zudaire et al, 2014) (see supporting information for detailed methods). Concentrations of triacylglycerols (TAG), free sterols (ST), and phospholipids (PL) were measured as μg/mg of wet weight (ww) (Parrish, 1999).…”

Relative survival of gags Mycteroperca microlepis released within a recreational hook-and-line fishery: Application of the Cox Regression Model to control for heterogeneity in a large-scale mark-recapture study

“…1998). These habitats also serve as important nursery areas, and as juveniles increase in size they leave the protection of seagrass beds and move into hard bottom habitats nearshore in the Gulf of Mexico (Stallings et al, 2010). Due to their life history and the high concentration of recreational fisheries in lower estuaries and nearshore, gags are vulnerable to fishing pressure at a young age.…”