Swimming activity and feeding behaviour of larval European sea bass (Dicentrarchus labrax L.): Effects of ontogeny and increasing food density.

The behaviour of European sea bass larvae reared with the mesocosm technique was analysed in relation to ontogeny and increasing food density, with a particular focus on swimming and feeding activities. The behaviour of groups of larvae (20 animals each) belonging to three age classes (10, 20 and 30 days post-hatching) was video-recorded in experimental tanks under controlled laboratory conditions.In each replicate, three different food densities, in terms of number of naupliar Artemia/l,were obtained. The videotapes analysis allowed the identification of 6 behavioural units (larval MAPs) and their quantification in terms of either frequency (number/min), or duration (percent of time spent in that activity with respect to the total time of observation). Behavioural variation was analysed in relation both to age and food density. Results revealed that swimming activity increased significantlywith age, especially between the 10 and the 20 days post-hatching, whereas resting activities decreased with age and, in some cases, also with food density. Frequency of feeding behaviour decreased with age if they were analysed singly, but when the association between aiming posture (Sigmoid-posture) and attacks was considered, results showed that these behaviours increased with both age and food density. Further, the increase of feeding efficiency with age was also confirmed by the increase in the number of Artemia nauplii/individual across the three age groups. Results are discussed in the light of both a comparative analysis conducted with the available data on the larval behaviour of other marine fish species, and their potential use for the assessment of the quality of the reared fish, also in relation to the rearing techniques.