Protein synthesis is one of the major energy-consuming processes in all living organisms. Post-prandial changes in protein synthesis have been studied in a range of animal taxa but have been little studied in fish larvae. Using the flooding-dose method, we measured post-prandial changes in whole-body rates of protein synthesis in regularly fed red drum Sciaenops ocellatus (Linnaeus) larvae for 24–28 h following their daily meal. Fractional rates of protein synthesis increased from a baseline (pre-feeding) rate of 16% day^–1 to a post-prandial peak of 48% day^–1 ca. 8 h after feeding before declining to 12% day^–1 after 24–28 h. The overall mean daily rate of protein synthesis was calculated as 27% day^–1. Although suggested as energetically impossible in larval poikilotherms, our results show that rates in excess of 30% day^–1 can be attained by larval fishes for a few hours but are not sustained. The average daily energetic cost of protein synthesis was estimated as 34% of daily total oxygen consumption, ranging from 19% immediately before feeding to 61% during the post-prandial peak in protein synthesis. This suggests that during the post-prandial peak, protein synthesis will require a large proportion of the hourly energy production, which, given the limited metabolic scope in fish larvae, may limit the energy that could otherwise be allocated to other energy-costly functions, such as foraging and escape responses.

The aim of this study was to evaluate the effect of environmentally realistic egg loadings of the polychlori- nated biphenyl Aroclor 1254 on the subsequent growth and behavioural survival skills of Atlantic croaker Micropogonias undulatus larvae. Adult fish were given a dietary administra- tion of 0 (control) or 0.4 (dosed) mg Aroclor 1254 kg -1 fish d -1 for 2 wk during the final stages of gonadal recrudescence. Fertilised eggs collected from control and dosed adults im- mediately after spawning contained 0 and 0.66 µg Aroclor 1254 g -1 egg, respectively. Growth rate (increase in total length) of dosed larvae was significantly lower than that of control larvae between 2 and 13 d post-hatching, with dosed larvae showing a 4 d delay in attaining the same size as con- trol larvae. Behavioural assays were conducted to evaluate survival skills of larvae on Days 5 (complete yolk absorption), 9 (complete oil globule absorption), and 13 (larva wholly dependent on exogenous food sources) post-hatching. Sur- vival skills examined were potential foraging rate (routine swimming speed and activity) and the response to a startle (transient vibratory stimulus) stimulus. Routine swimming speed and activity were similar for control and dosed larvae. There was a significant dose × age interaction in the responses of the control and dosed larvae to a vibratory stim- ulus. The percentage of control larvae responding to the stimulus, and their average and maximum burst speeds, increased with age. In contrast, no such age-related response was found in the dosed larvae. The results indicate that envi- ronmentally realistic body burdens of Aroclor 1254 transfer to the eggs and larvae, reducing their growth rates and impair- ing their startle responses, possibly making the larvae more susceptible to predation.