Daily feeding rhythms of Senegalese sole under laboratory and farming conditions using self-feeding systems

Although Senegalese sole is traditionally regarded as a night active fish, their daily feeding rhythm remains unknown. We therefore explored their ability to use self-feeders and their daily feeding rhythm under both indoors conditions and under farming outdoor conditions. First, the most suitable sensor for this benthic species was assessed under controlled conditions. The Senegalese sole were able to operate three different sensors: rod, string or optical. The most efficient was the string sensor, since this led to the lowest amount of food waste and the highest food demand levels, which occurred mostly (over 81%) at night. Consequently, the same sensor was tested in farming conditions using Senegalese sole reared in 5.6 m diameter circular tanks. These fish quickly learned to operate the self-feeders, reaching a stable feeding-demand level from the first day. When the food reward level (X) was modified (X/2, 2X), the fish displayed an accurate compensatory feeding behavior, increasing two-fold their feeding activity when the reward level was reduced to half or decreasing their demands by 50% when the reward level was doubled. Under farming conditions, food demands were mainly nocturnal (81%) and the uneaten feed was undetectable. In summary, Senegalese sole revealed their ability to use self-feeders and displayed a pronounced nocturnal feeding behavior regardless the experimental conditions, which should be taken into consideration when designing feeding strategies for this species.