Growth and energy budget of juvenile cobia (Rachycentron canadum) relative to ration

Growth, faecal production, nitrogenous excretion and energy budget of juvenile cobia (initial body weight 10 g or so) at five ration levels (starvation, 3%, 6% and 9% of initial body weight per day, and ad libitum) were investigated. Feed consumption, faecal production and growth of juvenile cobia were directly measured. Faecal production (f, mg g−1 d−1) increased with the increase of ration level (RL, % per day), described as ln(f+1)=1.1804 ln(RL+1)−0.0619. Feed absorption efficiency (FAE, %) decreased as ration level increased, but the variation of feed absorption efficiency (FAE, %) was small, with ranges of 81.44–87.17% 96.57–98.377%, and 94.21–96.54% for FAEd, FAEp, and FAEe, respectively. The relationship between ration level (RL, % per day) and specific growth rate in wet weight (SGRw, % per day), dry weight (SGRd, % per day), protein (SGRp, % per day) and energy (SGRe, % per day) were decelerating curves described as logarithmical equations: SGRw=3.8759 ln(RL+1)−3.7164, SGRd=5.1068 ln(RL+1)−5.2477, SGRp=5.5611 ln(RL+1)−5.6094 and SGRe=6.1282 ln(RL+1)−7.4385. Feed conversion efficiency in wet weight (FCEw, %), dry weight (FCEd, %), protein (FCEp, %) and energy (FCEe, %) increased with ration level, peaked at 9% per day ration and then decreased at higher ration level. Energy intake (C), energy retained as growth (G) and energy lost in faeces (F) were estimated directly and energy allocated to excretion (U) and metabolism (R) were calculated by difference (U+R)=C−F−G. The partial energy budget of juvenile cobia at satiation ration was 100C=7F+76(U+R)+17G.