Elevated oxygen uptake and high rates of nitrogen excretion in early life stages of the cobia Rachycentron canadum (L.), a fast-growing subtropical fish

Physiological energetics of cobia Rachycentron canadum were quantified for 18 to 82 days posthatch (dph) hatchery-reared juveniles to better understand energy transformation and its implications in growth and survival. Mean oxygen consumption rates (MO2 ; mg O2 h ) of fish fed ad libitum and fish that were starved significantly increased with increasing wet mass (M; g), MO2 1⁄4 1 4291M 8119 andMO2 1⁄4 1 1784M , respectively, with a significant reduction in mean metabolic rates of starved fish (19 to 27%specific dynamic action; SDA). Total ammonia nitrogen excretion rates (AMM, mmol h ) also scaled with M and significantly decreased after starvation. Mean mass-specific AMM and urea excretion rates are the highest reported in the literature, with urea accounting for approximately half the total nitrogen excretion measured in both fed and starved fish. Relatively high energetic rates may allow cobia to develop rapidly into pre-juveniles and be less susceptible to predation and starvation at a comparatively early age. # 2007 The Authors