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 N. Villamizar a , G. García-Mateos b , F.J. Sánchez-Vázquez a, ⁎ a Department of Physiology, Faculty of Biology, University of Murcia, Campus Espinardo, 30100 Murcia, Spain b Department of Computer Science, Faculty of Computer Science, University of Murcia, Spain abstract article info Article history: Received 9 November 2010 Received in revised form 24 March 2011 Accepted 28 March 2011 Available online 6 April 2011 Keywords: Fish larvae Feeding behavior Light spectrum Photoperiod Prey behavior 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Although organism responses to light have often been ascribed to one basic mechanism (i.e. visual processing), the regulation of circadian rhythms by light led to the discovery of non-visual photoreceptors that are involved in several physiological processes related to the task of extracting seasonal and time-of-day information (Foster et al., 2007). In fish, the photosensory systems and extraretinal photoreceptors are complex and far from fully understood, as the response to light is often species-specific, depending on phylogenetic and ecological factors (Marchesan et al., 2005). Scarce information about the features of the environmental light and the photoresponse behavior of fish, particularly at the larval stage, makes the interpre- tation and correlation of existing data a difficult task. In nature, the spectral characteristics of underwater light are determined by a combination of the ambient skylight and the optical properties of the water. Light becomes increasingly monochromatic with depth, because the spectral profile is selectively attenuated as light passes into deep water (Jerlov, 1968). Thus, clear ocean waters transmit maximally at blue wavelengths (470 nm), while coastal waters transmit better at blue-green wavelengths (500 nm) and estuarine waters at green wavelengths (580 nm) (Cohen and Forward, 2002). Furthermore, fish have adapted their photopigment sensitivity accord- ing to their surrounding environment (Kusmic and Gualtieri, 2000). European sea bass (Dicentrarchus labrax) is one of the most widely cultured fish species of the Mediterranean Sea and large numbers of larvae are produced at industrial level. However, the impact of environmental factors such as lighting conditions is poorly understood, although recent work reviewed the response to certain light spectra, intensities and photoperiod, which were seen to have a great influence in terms of larval growth, development and survival (Villamizar et al., 2011). Nevertheless, the behavioral responses of larvae and their prey under different lighting conditions remain unexplored. The aim of this research was to investigate the Modal Action Patterns (swimming duration, orientation, capture, miss and pass frequencies) and distribution of sea bass larvae from 1 day post hatching (DPH) to 30 DPH; exposed to different light spectra and photoperiod. In addition, live prey (Artemia) hatching and distribution Aquaculture 317 (2011) 197–202 ⁎ Corresponding author at: Department of Physiology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain. Tel.: +34 868 887004; fax: +34 868 883963. E-mail address: javisan@um.es (F.J. Sánchez-Vázquez). 0044-8486/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2011.03.036 Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online