Daily rhythms of locomotor activity, feeding behavior and dietary selection in Nile tilapia (Oreochromis niloticus)

Fish do not feed at any time of the day and on whatever food item they encounter in the wild, but they show daily rhythms of feeding activity and dietary selection. The aim of this research was to investigate the daily rhythms of behavior in Nile tilapia self-fed with plant-based diets supplemented with different levels of exogenous phytase (an enzyme that hydrolyzes non-digestible phytate and improves the nutritional value of the diet). To this end, ten males were individually kept in 50-L tanks, each equipped with two self-feeders and one infrared photo-cell connected to a computer. The selection factors investigated were the level of phytase supplementation (0 IU kg(-1) vs 1500 IU kg(-1); 1500 IU kg(-1) vs 4000 IU kg(-1)) or sodium phytate (1% phytate vs 1% phytate+1500 IU kg(-1) phytase). The results revealed that 66.7% of total daily activity occurred during the day, while feeding was strictly nocturnal, with 93.0% of the daily food demands occurring at night. Tilapia preferred the diet with 1500 IU kg(-1) phytase rather than the control or 4000 IU kg(-1) diets. When exogenous sodium phytate was added to the diet, tilapia preferred the phytase diet. In conclusion tilapia self-feed at night (although locomotor activity was mostly diurnal) and chose plant-diets containing phytase, which should be taken into account when designing feeding strategies and practical diets for tilapia aquaculture.