Effect of water temperature on energy budget of Nile tilapia, Oreochromis niloticus

A 21-day growth trial was undertaken to investigate the effect of water temperature (25, 28, 31, 34, 37 degrees C) on growth, feed utilization and energy budget of juvenile Nile tilapia (Oreochromis niloticus) (initial body weight around 12 g) with four replicates at each temperature. Feed intake energy (IE), recovered energy (RE), faecal energy (FE), excretory energy (UE + ZE) and heat energy (HE) were calculated to obtain the energy budget. The results showed that feeding rate and ammonia excretion were not significantly affected by water temperature. Specific growth rate in wet weight (SGRw) and FE was significantly lower in the fish reared at 37 degrees C while no significant difference was observed between the fish reared at 25-34 degrees C. Protein retention efficiency was highest at 28 degrees C and lowest at 37 degrees C. The proportion of IE channelled into RE and UE + ZE was lower while those lost in HE was higher in the fish reared at 37 degrees C. The optimal growth temperature was estimated as 30.1 degrees C based on the regression of SGR and water temperature. Energy budget at maximum growth (34 degrees C) was: 100 IE = 27.0 RE + 1.1 (ZE + UE) + 10.6 FE + 59.2 HE. HE accounted for 69.3% and RE for 30.7% of metabolizable energy.