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

Abstract

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 O 2 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 O 2 mg − 1 protein synthesised. Total protein synthesis expenditure (74.5–77.7 μmol O 2 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.