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Fish have an internal biological clock that drives their daily rhythms, including those of feeding and reproduction. The European sea bass has been reported to exhibit a phase inversion of its diel feeding pattern: nocturnal in winter (coinciding with the spawning period) and diurnal during the remainder of the year. In this study, we investigated the locomotor activity of sea bass during the spawning and resting periods as well as the possible existence of a daily spawning rhythm by calculating the number of eggs (and their viability) released every hour. The results showed that sea bass locomotor activity was clearly nocturnal (68 ± 4.3% of the daily activity displayed at night) during the spawning season and mostly diurnal (65.5 ± 7.5% of the activity displayed during the day) out of the reproductive period. Spawning occurred during the dark phase with two peaks, 6 and 11 h after lights off. Egg viability was highest in the batch released near the spawning peaks. These findings could be useful for optimizing egg production and to improve hatchery practices, which should take into account the reproduction rhythms of sea bass.

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 LD B the phototactic response of sea bass larvae led to a significatively homogeneous distribution in the tanks and aquaria, while under LD W and LL the highest larvae density (52%) was seen on the tank walls. LD B and LD W 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.

Light is a key environmental factor that synchronizes all life-stages of fish, from embryo development to sexual maturation. The underwater photo-environment is complex since light characteristics (i.e. intensity, photoperiod and spectrum) depend on the absorbance properties of the water column. The aim of this paper is to review the effects of artificial lighting conditions on the performance, development and welfare of some fish larvae of commercial interest. Reviewed results show that larvae were significantly affected by light characteristics. For example, European sea bass and sole larvae achieved the best performance, and showed fastest development and lowest degree of deformity under a light/dark cycle using blue light (half-peak bandwidth = 435–500 nm), conditions which were the closest to their natural aquatic environment. However, constant light (LL) or constant darkness (DD) was shown to negatively affect normal larval development and resulted in increased malformations and poor survival in most of the studied species. Similar results have been observed in other fish larvae such as Atlantic cod, which performed better under short wavelengths (blue and green). These findings highlight the role of lighting conditions during the early development of fish larvae and should be taken into account for the optimization of rearing protocols in fish hatcheries as juvenile supply is one of the main production bottlenecks.

36 p., il., y bibliografía, This paper investigates the impact of different thermo- and photo-cycles of distinct wavelengths on Solea senegalensis larvae from day 1 to 30 post-hatching. In experiment 1, larvae were exposed to 12h light:12h dark (12L:12D) cycle and (A) constant temperature (20.7°C), (B) thermocycle of 12h thermophase: 12h cryophase, 22.1°C day: 19.0°C night (referred to as TC) or (C) 12h cryophase: 12h thermophase, 19.2°C day: 22.0°C night (referred to as CT). In experiment 2, larvae were kept under constant temperature (20.8°C) and exposed to (A) continuous light (LL), (B) continuous darkness (DD), and LD 12L:12D cycles of (C) white light (LDW), (D) blue light (LDB) or (E) red light (LDR). The sole larvae achieved the best performance, and showed fastest development and lowest degree of deformity under natural thermocycle conditions (TC) with a deformity percentage of 31.1% and LDB cycles with 27.7% of malformation, conditions which were nearest their natural aquatic environment. Larvae reared under TC started eye migration at 9day post-hatching (DPH), while larvae exposed to CT started eye migration at 11 DPH. In larvae under the LDB treatment the migration of the eye started earlier than in the other treatments (9 DPH), while larvae reared under LL and DD photoperiods died before metamorphosis. These findings highlight the importance of light and temperature cycles during the early development of S. senegalensis larvae, which should be taken into consideration in experimental or rearing protocols., This research was funded by the Spanish Ministry of Science and Innovation (MICINN) by projects “Circasole” AGL2007-66507-C02-02 and AQUAGENOMICS 28502 (Consolider-Ingenio Program), and SENECA by project 05690/PI/07 to Francisco Javier Sánchez Vázquez.