Effects of ration and temperature on growth, fecal production, nitrogenous excretion and energy budget of juvenile cobia (Rachycentron canadum)

A 4x3 factorial experiment was conducted for two weeks to determine the effects of ration level ranging from starvation to satiation and water temperature at 21, 27 and 33 degrees C on growth, fecal production, nitrogenous excretion and energy budget of 10-g-size cobia in this study Over the temperature range, 21-33 degrees C, maximal ration (R-max, % per day), optimal ration (R-opt, % per day) and maintenance ration (R-maint, % per day) all increased with temperature (T, degrees C), described as a quadratic equation R-max = -0.046T(2) + 2.906T-35.97 (R-2 = 0.989). a simple equation R-opt = -0.533T-8.001 (R-2 = 0.993), and a quadratic equation R-maint = 0.028T(2) - 1.350T-17.18 (R-2 = 1), respectively Both fecal production (f mg g(-1) d(-1)) and nitrogenous excretion (u, mg g(-1) d(-1)) were affected significantly by ration and temperature and increased as ration and temperature increased. Feed absorption efficiency (FAE, %) varied small over the whole ration and temperature ranges though the effects of ration and temperature were significant in some data. Juvenile cobia grew fastest at 33 degrees C when fed at satiation but the growth rate was equal or better at 27 degrees C when food was restricted, whereas the fish showed overall significant lower growth rates at 21 'C except for the starved treatment. Among three temperatures specific growth rate in wet weight (SCRw, % per day), dry weight (SGR(d), % per day), protein (SGRp, % per day) and energy (SGR(e), % per day) all increased with ration, showing decelerating growth-radon relationships described as logarithmical equations at 27 and 21 'C and a linear growth-ration relationship described as a simple equation at 33 'C. Apart from starvation ration with a negative linear growth-temperature relationship growth all increased with temperature, described as quadric functions. Two-way ANOVA showed that ration and temperature had an interaction on growth. By using multiple regression analysis the relationships between specific growth rate (SGR, % per day) and ration level (RL, % per day) as well as temperature (7) took the forms: SGR, = - 11.97 + 1.231n(RL + 1) + 0.91T -0.02T(2)+0.16Tln(RL+1) (R-2 =0.962), SGR(d) = -17.04 + 0.72ln(RL+1) + 1.11T-0.02T(2) + 0.12Tln(RL+1) (R-2=0.968), SGR(P)=-18.25 + 0.20ln(RL+1)+1.28T-0.03T(2)+0.15Tln(RL+1) (R-2=0.972) and SGR(e) = -20.83+0.851n(RL+1)+1.40T-0.03T(2)+0.157ln(RL+1) (R-2=0.969). Feed conversion efficiency in wet weight (FCEw, %), dry weight (FCEd, %), protein (FCEp, %) and energy (FCEe, %) at 27 and 33 degrees C was much higher than that at 21 degrees C, and the maximal FCE occurred at sub-satiation (i..e. feeding group 3) and 27 degrees C. All the relationships between FCE and temperature were described as quadric equations. Energy budgets of juvenile cobia at satiation ration were: 100C = 7.0F + 7.7U + 69.0R + 16.4G (or 100A = 81R + 19G) at 33 degrees C, 100C = 6.8F + 7.9U + 68.0R + 17.3G (or 100A = 80R + 20G) at 27 degrees C and 100C = 63F + 8.4U + 77.2R + 82G (or 100A = 90R + 10G) at 21 'C, where C is food energy, A is assimilated energy, F is feces energy, U is excretion energy, R is metabolism energy and G is growth energy. (C) 2009 Elsevier B.V. All rights reserved.