No efficiency of the lateral system on nocturnal feeding in the European sea bass (Dicentrarchus labrax L.)

In order to evaluate the effect and consequence of lateral system inactivation on fish nocturnal feeding, the differential growth of groups of European sea bass maintained in different rearing conditions were compared. Whereas some fish with intact lateral system (placebo fish) were placed under a photoperiod of 12-L: 12-D, other placebo fish were kept in the dark. In the same way, fish deprived of lateral system by section of their lateral system nerves and antibiotic treatment were placed under a photoperiod of 12-L :12-D and the others in the dark. For each of these four rearing conditions, two sets of experiment were realized. Percent mortality, feed rhythm, averaged daily feed demand, specific growth rate and feed efficiency were compared among these four groups of fish. After four months of experiment, results revealed that, under a
photoperiod of 12-L: 12-D, fish showed a diurnal feed rhythm whereas no rhythm appeared in fish kept in the dark. In addition, as reported by other authors, the average daily feed demand, the quantity of ingested food and specific growth rate were greater in fish maintained under a photoperiod of 12-L :12-D than those kept in the dark. The fish lateral system inactivation did not affect mortality, feed intake, specific growth rate or feed efficiency. These results demonstrated that lateral system is not the major sensory organ leading to European sea bass nocturnal feeding; chemoreception system undoubtedly taking over. If the olfactory system explains equal feed intake between placebo and treated fish, the greater specific growth rate in treated than in placebo fish indicates the action of another mechanism, such as a "booster effect" of
antibiotics used for lateral system inactivation on fish.