Life as a larva is risky: you're on the menu for many species. Yet it's the time when you need to put most of your effort into growing and developing, rather than simply staying alive. So exactly how much energy do fish larvae invest in growth and development and how much energy does that leave for other processes, such as swimming and foraging? More specifically, how much do they invest in costly protein synthesis when their energy resources are limited? Ian McCarthy and Lee Fuiman explain that protein synthesis is a major metabolic cost when digesting and processing a meal. The duo decided to measure protein synthesis rates in red drum larvae as they digested brine shrimp dinners to find out how much of their energy budget they invest (p. 1821). Plotting the larval protein synthesis rates for 24 h after the larvae fed, McCarthy and Fuiman found that the fractional protein synthesis rates (the amount of free amino acid converted into protein) rose from 16% day–1 prior to eating to a staggering 48% day–1 around 8 h after the meal, before falling back to 12% day–1 16 h later. And when the duo calculated the amount of energy that the larvae invested in digesting dinner, they were amazed to see it rocketed to 61% of the larvae's oxygen consumption during the peak periods of protein synthesis.

The duo say, ‘Although suggested as energetically impossible in larval poikilotherms, our results show that rates [of protein synthesis] in excess of 30% day–1 can be attained by larval fish for a few hours.’ They also add that diverting this enormous amount of energy to protein synthesis could impact on other activities, such as foraging and fleeing.

I. D.
L. A.
Post-prandial changes in protein synthesis in red drum (Sciaenops ocellatus) larvae
J. Exp. Biol.