Behavioral responses of European sea bass (Dicentrarchus labrax) larvae and Artemia sp. exposed to constant light or darkness vs. light/dark cycles of white, red or blue wavelengths

The performance and survival of fish larvae are strongly influenced by their surrounding photic environment. The aim of this study was to investigate the effect of light characteristics (spectrum and photoperiod) on the feeding and locomotor behaviors of European sea bass larvae and its prey (Artemia sp.). To this end, constant light (LL), constant darkness (DD) and 12:12 h LD cycles of red, blue or white LED lights were applied from 1 to 30 days post-hatching. The Modal Action Patterns (swimming duration, orientation, capture, miss and pass frequencies) of larvae and Artemia distribution in the tank were video recorded and analyzed using newly developed tracking software. The results showed that under LDB the phototactic response of sea bass larvae led to a significatively homogeneous distribution in the tanks and aquaria, while under LDW and LL the highest larvae density (52%) was seen on the tank walls. LDB and LDW resulted in longer swimming duration and earlier weaning. Larvae exposed to darkness and red light showed the lowest swimming and feeding activity, and a higher aggregation tendency of both fish larvae and the live prey. White light exposure resulted in a strong phototactic response from fish larvae and Artemia, which consisted of a tendency to congregate at the corners or close to the walls of the tank/aquaria. Artemia hatching rate under blue light was highest (56.5 ± 2.9%) in contrast with red light (26.3 ± 1.4%) and total darkness (27.9 ± 3.9). These results showed that the relationship between the behavioral responses of sea bass larvae and Artemia is strongly affected by lighting conditions, which has both basic and practical implications for understanding their behavioral ecology and for improving culture protocols.