Metabolic costs of changing the cation-anion difference in the diet of juvenile African catfish Clarias gariepinus (Burchell)

The influence of dietary cation-anion difference (CAD, Na K - Cl, mEq kg1) on energy metabolism and nitrogen losses in juvenile African catfish Clarias gariepinus (Burchell) was examined in fish exposed to different dietary CAD levels (-146, 116, 497, 713 and 828 mEq kg1 diet). The experiment was conducted in open circuit balance respiration chambers over a 3-week period. Five 24-h monitoring periods were carried out at 3-day intervals during the experimental period with O2 consumption, ammonia and nitrate nitrite (NOx) and CO2 production being measured at 5-min intervals for each chamber. The negative dietary CAD (-146 mEq kg1) resulted in the highest energy expenditures (83 kJ kg0.8? d1). With increasing dietary CAD levels, heat loss gradually decreased to minimum values of 56 kJ kg0.8 day1 at a dietary CAD level of 713 mEq kg1. Consequently, metabolizable energy utilization efficiency (MEU, percentage of retained energy over metabolizable energy) quadratically (P < 0.05) increased and reached a maximum at a dietary CAD of 713 mEq kg1