ADVANCES IN THE CONTROL OF PUBERTY AND REPRODUCTIVE CYCLE IN EUROPEAN SEA BASS, DICENTRARCHUS LABRAX

摘要

European sea bass is an important marine aquacultured species. The scientific knowledge on its biology, reproduction and growth together with significant advances in outdoor culture technologies have allowed a production of around 88.000 MT in 2006 (Aquamedia, 2007). Furthermore, improvement in brookstock management, husbandry, nutrition, and feeding strategies resulted in more suitable progenies with better growth performances. Despite these favourable conditions, there are still problems that affect the productivity under culture. Most farmed sea bass populations are skewed, 75% or more, to males. Many of them exhibit an early puberty and produce sperm at their first annual cycle (Carrillo et al 1995). This is concomitant with the belief that rapid growth in fish may reduce the age of first sexual maturity (Fleming, 1996). This seems to be the case in sea bass as precocious males are significantly larger than non-precocious (Begtashi et al,. 2004). Also, premature fish grow less than thek counterparts during their second annual cycle of life (Felip et al., 2006). In the best of the cases, male sea bass reach puberty around the second year of life by the time of commercial size (400-500 g). Onset of puberty may involve muscle wasting, slow growthand loss of flesh quality. Moreover, mature males represent an environmental and quality product concern because spermiating fish can genetically pollute wild stocks and affect the hygienic condition of the product. Female sea bass reach puberty one year later than males and exhibit better growth rate at the same age (Carrillo et al., 1995). But, under intensive culture certain number of them exhibit vitellogenic ovaries at the second year of life (M. Carrillo and S. Zanuy personal observation). Also nowadays, market asks for larger fish and this entails a serious problem in females because the important ovarian growth at puberty. A good strategy to beat these problems would be prevent sea bass puberty. Photoperiod has shown to be one of the most important cues regulating this process by acting on the brain-pituitary-gonadal (BPG) axis (Zanuy et al., 2001; Felip et al., 2008). Sea bass has a seasonal reproductive strategy and generally breeds spontaneously in captivity. Albeit, reproduction is restricted to a few months, this limits its farming since supply of eggs is needed through the year. Yet, some hatcheries do not fit the necessary environmental conditions for natural breeding. In these, manipulation of photoperiod and temperature are used totrigger spawning of sea bass. Hormonal therapies have been used successfully alone or combined with environmental regimes to synchronize reproduction (Fournies et al., 2001, Mylonas et al.,unpubl.). Recently sea bass gonadotropin (GtH) subunits have beencloned (Mateos et al., 2003) and recombinant GtHs produced (Moles et al., 2005). Further, somatic gene transfer has shown to be an efficient method for in vivo delivery of LH into fish blood (Gomez et al., 2004). Here, we review the latest results on environmental control of the first maturation and reproductive cycle of sea bass. The use of recombinant single chain LH (LHsc) and the somatic gene transfer methodologies as new hormonal therapies are also discussed.