Individual and combined effects of hypoxia and hypercapnia on feeding and feed utilization in Nile tilapia (Oreochromis niloticus)

Photosynthesis and respiration exert strong opposing effects on dissolved gases in earthen ponds. During daylight this provides oxygen to the water while removing carbon dioxide. At night, fish, plankton, sediment consumes available O2 produces CO2. This leads daily conditions that fluctuate between being hyperoxic hypocapnic during day, becoming severely hypoxic hypercapnic at night. The of hypoxia Nile tilapia have been examined some detail, but interacting hypercapnia fluctuating conditions, not received any attention. Here we evaluated variations CO2 appetite feed utilization using groups reared under normoxic - normocapnic (control, C), diurnal (HO), (HC), or combined (HO × HC) a digestibility system. We show exerted individual appetite, specific growth rate, conversion, simultaneous amplified these effects. Appetite depression induced by nocturnal was restored mid-day, exposure resulted day-long loss appetite. Hypoxia reduced rates up 40% increased conversion ratio 80%, rate >60%. Surprisingly, dry matter, protein, lipid improved exposed single variation It is unknown whether result change intake represents an adaptive mechanism satisfy increase energy demand caused environmental stress. Overall, conclude although considered resilient stress, feeding are strongly influenced fluctuations gases.