Effects of light intensity on performances, larval development and foraging activity in common sole (Solea solea) larvae

Abiotic factors, have shown to play a significant role in fish larval rearing Setting environmental parameters specific for each species can improve performances and survival. Among them, light intensity seems to influence growth and survival during the early development of fish larvae since different studies have shown that most marine fish larvae are visual feeders. This study investigated the possible effect of light intensity on performances, development and foraging activity on Solea solea larvae from day 4 to 51 post-hatching. Four treatments were tested in triplicate in order to applied different light intensity regimes (LRs): light intensity of 1000 lx (LR1000), light intensity of 500 lx (LR500), light intensity of 50 lx (LR50) and light intensity of 3 lx (LR3). Larvae were exposed to 16 h light : 8 h dark photoperiod and were kept under constant temperature (18 °C). Feeding protocol for all treatments consisted in live feed (Artemia spp.) until 18 dph followed by weaning onto commercial microdiet. Sole larvae reared under high light intensity (L1000 and L500) showed a high weight gain during the first period, whereas after metamorphosis best performances were achieved under low light intensity (L50 and L3). Mortality rates were lower in L50 and L500. No abnormalities of development were detected in the different treatments. Organs development, with special regard to sensory organs as eyes, olfactory sensory cells, otic vesicles, neuromasts, taste buds and barbells was also evaluated by histological analysis all trough the trial.Results suggest that light intensity for sole larvae should be high (500-1000 lux) during the first rearing period and lowered (50-3 lux) after metamorphosis completion. This could indicate that sole is a preferential visual feeder during the larval pelagic phase while after metamorphosis other sensory organs are mainly involved in foraging activity.