Combined effect of temperature and salinity on energy metabolism of GIFT Nile tilapia (Oreochromis niloticus) juveniles

Abstract

We evaluated the combined effects of temperature and salinity on the energy metabolism of Nile tilapia juveniles(Oreochromis niloticus,GIFT strain).We used a two-factor central composite experimental design(CCD) and response surface methodology(RSM) to test the effects of temperature(13–36℃) and salinity(0–20) on the oxygen consumption rate(OR),ammonia excretion rate(NR),and CO2 excretion rate(CR) under laboratory conditions.The linear effects of temperature and salinity,the quadratic effect of salinity,and the interaction be-tween salinity and temperature had significant effect on OR,NR and CR(P0.05).The quadratic effect of tem-perature was not associated with changes in OR and CR(P0.05).The model equations for OR,NR,and CR had R2 values of 0.958 1,0.977 8,and 0.979 5,respectively(P0.01),and could be used for prediction.The OR,NR,and CR were influenced more by temperature than by salinity.At lower salinities,energy metabolism was sensi-tive to changes in temperature,and OR,NR,and CR were higher around the iso-osmotic point.However,when salinity exceeded the iso-osmotic point,lower temperatures and higher salinity inhibited metabolism.The O∶N ratio did not vary with temperature,but vary with salinity(P0.05).Within the temerature range of 13–36℃ and salin-ity range of 0–10,tilapia juveniles utilized protein-lipid-dominated metabolism.Conversely,the juveniles depended on lipid-dominated catabolism at salinity of 20.The mean respiratory quotient value was 0.752.Our results pro-vide insight into the joint influence of temperature and salinity on the metabolism of tilapia juveniles and provides a bioenergetic basis for the study of how environmental factors govern the spatial and temporal pattern of energy distribution in this species.