Effect of light spectrum and photoperiod on the growth, development and survival of European sea bass (Dicentrarchus labrax) larvae

Abstract

This study investigates how the characteristics (spectrum and photoperiod) of artificial light affect European sea bass eggs and larvae from − 1 to 40 days post-hatching. Fertilised eggs and larvae were reared under five different light treatments: 12L:12D red light (LDR; half-peak bandwidth = 641–718 nm), 12L:12D blue light (LDB; half-peak bandwidth = 435–500 nm), 12L:12D broad-spectrum white light (LDW; 367 < λ < 1057 nm), 24L:0D broad-spectrum white light (LL) and 0L:24D (DD). The results showed that total length at day post-hatching 40 was significantly larger in larvae reared under LDB (15.4 ± 0.6 mm) and LL (15.2 ± 0.6 mm) than in larvae reared under LDR (11.7 ± 0.7 mm). Overall wet weight was highest under LDB (21.6 ± 2.02 mgr) and lowest in LDR larvae (13.6 ± 1.48 mgr). Yolk sac and oil globule absorption occurred more slowly in LDR and DD larvae, while LDB larvae developed their fin, teeth and swim bladder significantly earlier than the rest of the groups. DD larvae were unable to capture food and mortality was 100% by day post-hatching 18, while LDR larvae did not feed on rotifers, but fed on Artemia from day post-hatching 16 onwards. The best survival was obtained with the LL treatment, although significantly more problems with swim bladder development and lower jaw malformations were also identified in this group. In summary, these results highlight the key role of the light spectrum and photoperiod for European sea bass larvae, the best performance being achieved under the light conditions that best approached those of their natural aquatic environment (LDB). These findings should be considered when designing rearing protocols for larvae in aquaculture.

Introduction

The day and night light cycle is one of the main environmental challenges that every organism has to cope with in order to survive in nature. To this end, light-sensitive circadian clocks have evolved in most animals, including fish. Light cycles provide internal synchronization for the rhythmic synthesis and release of time-keeping hormones (i.e. melatonin), whose signal affects rhythmic physiological functions in fish (Bromage et al., 2001). Under artificial rearing conditions, however, lighting regimes are established by fish farmers according to the benefits in terms of survival and growth, as long documented in many cultured species (Barahona-Fernandes, 1979, Tandler and Helps, 1985, Batty, 1987, Downing and Litvak, 1999). Nevertheless, little attention has been paid to the influence of “unnatural” light conditions (constant light or darkness) and light characteristics (yellow/reddish spectral composition), even though they are known to affect the development of fish larvae and their circadian clock (Vallone et al., 2007).

The water column acts as a chromatic filter, and so the aquatic environment dramatically changes the spectral composition of incident light. There is rapid attenuation with depth, so blue wavelengths become predominant in all but the most shallow or turbid waters (Jerlov, 1968). In contrast, standard lighting systems commonly used in hatcheries create bright point light sources that are neither environment-specific nor species-specific and could potentially compromise fish welfare. Moreover, much of their light energy is wasted in the form of unsuitable wavelengths (e.g. longer wavelengths, yellow–red light) which are rapidly absorbed by water molecules and therefore cannot be detected by fish (Loew and McFarland, 1990, Migaud et al., 2006). Light emitting diodes (LEDs) are currently being developed for the fish farming industry since they can be tuned to environmental and species sensitivities through narrow bandwidth outputs. It has been suggested that LEDs focusing on the blue–green spectrum may be most suitable, as these wavelengths generally penetrate seawater more efficiently (Migaud et al., 2007). However, prior to implementing these new alternatives, any potentially adverse effects must be determined in fish larvae.

Several studies have investigated the impact of light on cultured finfish larvae and showed that light affects larval foraging and subsequently their growth and survival (Puvanendran and Brown, 2002, Monk et al., 2006, Yoseda et al., 2008). Moreover, inappropriate light intensity and spectra during the early development of teleost fish are linked with a number of skeletal abnormalities (Battaglene and Talbot, 1990, Liu et al., 1994.) and the absence of a functional swimbladder (Cerqueira and Chatain, 1991, Battaglene et al., 1994, Trotter et al., 2003).

European sea bass is one of the most intensively cultured species and recent advances in the field have allowed the setting of several abiotic conditions, although the response to certain light intensities and photoperiods have shown that they may not only have a positive but also a negative influence in terms of early development and survival (Barahona-Fernandes, 1979, Ronzani Cerqueira et al., 1991). Despite the evidence of the impact of light quantity, no model to date has incorporated the influence of light quality on European sea bass larvae or its interaction with important aspects like growth, development, prey ingestion and survival.

The aim of this study was to investigate the effects of different light spectra and photoperiods on European sea bass eggs and larvae exposed to white, blue or red light in 12L:12D cycles, constant light or constant darkness from − 1 day to 40 days post-hatching (DPH).