Growth, oxygen consumption, and protein and RNA synthesis rates in the yolk sac larvae of the African catfish (Clarias gariepinus)

Rapidly growing African catfish yolk sac larvae were investigated during the first 22 h after hatching. Body compartment protein concentration increased fourfold yet oxygen consumption remained constant (mean = 21.3 ± 3.2 nmol O2 mg− 1 protein h− 1), suggesting fast growth results mainly from yolk sac protein absorption. The protein synthesis rates at 1–2 and 5–6 h also equaled the highest conceivable rates of muscle protein synthesis; 11.6–11.9% and 7.4–7.9% day− 1, respectively. Therefore the corresponding energetic costs of protein synthesis were almost the theoretical minimum; 13.0 ± 1.7–16.3 ± 2.8 μmol O2 mg− 1 protein synthesised. Total protein synthesis expenditure (74.5–77.7 μmol O2 g− 1 protein h− 1) was also less than other yolk sac larvae. These protein synthesis rates resulted from high RNA concentrations (113.2 ± 3.4 μg RNA mg− 1 protein) and were also correlated with RNA translational efficiency. High translational efficiency (1 h; 1.2 ± 0.1 mg protein synthesised μg− 1 RNA day− 1) equaled high synthesis rate (36.8 ± 5.4 μg RNA μg− 1 DNA day− 1) and both declined over 22 h. This investigation suggests rapid growth combines growth efficiency and compensatory energy partitioning. This accommodates the ontogenetic and phylogenetic standpoints imposed by energy budget limitations.