Lucinda Rodrı́guez

Influence of daylength on the age at first maturity and somatic growth in male sea bass (Dicentrarchus labrax, L.)

Groups of 4-month-old sea bass were each exposed over three consecutive years to a natural photoperiod (40°N) (NP), constant long photoperiod (15L:9D) (LO) and 18-month-expanded photoperiod (the natural light cycle extended to 18 months) (EX), under natural conditions of temperature (12.0–26.3°C). During the differentiation period, a significant increase in number of precocious males was found in the LO (26.8%) and EX (17.7%) groups compared to controls (5.3%) (P 80%). At the second reproductive period (32–37 months of age) gonadal maturation was advanced in EX group, whereas a significant delay was observed in LO group with respect to control. Spermiation in EX group was advanced with respect to control group. During the second reproductive period, percentage of spermiating males was significantly higher in EX group (∼80%) than in LO group (<50%). LO and EX groups displayed enhanced growth (655.52±37.21 g and 376.40±6.33 mm; 510.44±25.80 g and 350.14±5.27 mm, respectively) compared to controls (459.93±21.20 g and 343.62±4.82 mm). The present results indicate a significant beneficial effect of constant long and expanded photoperiods on reducing sea bass gonadal development and enhancing growth at the age of commercialisation, with a potential application in aquaculture.

Genetic, hormonal and environmental approaches for the control of reproduction in the European sea bass (Dicentrarchus labrax L.)

The European sea bass Dicentrarchus labrax is a very important commercial fish in Europe, the production of which by aquaculture has increased several fold during the last decades. Studies on biology, control of reproduction, broodstock management, offspring quality and rearing techniques, as well as large investments in the aquaculture sector, have made possible this rapid increase in production. However, under culture conditions, there are still important problems that negatively influence its industrial production. These are: (1) high percentage of males (70–90%), some of which are precocious at the first year of life; (2) in males, puberty typically appears in the second year of life (at commercialization), 1 year before females; and (3) males grow less than females, being 40% lower in body weight at harvest time. Consequently, reduction of the number of males and/or production of all-female stocks and sterile fish and prevention of puberty are highly desirable goals. The present work reviews the latest scientific advances on the genetic and physiological control of the sex and the process of puberty in the sea bass to provide tools to alleviate some shortcuts in its industrial production.

Changes in plasma levels of reproductive hormones during first sexual maturation in European male sea bass (Dicentrarchus labrax L.) under artificial day lengths

Abstract Photoperiod has been considered one of the most important factors triggering puberty, as well as reproduction, in several fish species, including sea bass ( Dicentrarchus labrax L.). In the present work, the effect of expanded (EX) and compressed (CO) photoperiods on plasma levels of reproductive hormones (gonadotropin-2 (GTH-2), testosterone (T) and 11-ketotestosterone (11-KT)) and gonadal maturation (spermiation time and gonadosomatic index (GSI)) were investigated in male sea bass during the first sexual maturation (October to April). Spermiation in controls was apparent from December to February–March. In EX and CO groups, spermiation was advanced by 2 months, although the CO group displayed a bimodal pattern, and testicular growth in both experimental groups was significantly reduced with respect to the controls. Plasma GTH-2 levels in controls showed the highest value (∼30 ng/ml) in the middle of the spermiation period, while EX group displayed the maximum level 4 months earlier (35±2.7 ng/ml) than controls. The CO group presented two peaks, the first of which (15.16±5.20 ng/ml) was advanced by 3 months with respect to the control peak. T and 11-KT levels in the control displayed the highest values during the spermiation period. The EX group showed lower T levels than controls, but both peaked at the same time. However, 11-KT levels remained low and unchanged. The CO group displayed two significant increases in T levels accordingly with the spermiation pattern, while the 11-KT profile only exhibited a significant increase 2 months earlier than in controls. Results obtained indicated an involvement of GTH-2 in gonadal maturation. In addition, T is suggested to be involved in the activation of the brain–pituitary–gonad (BPG) axis during pubertal development, while 11-KT may act by stimulating spermatogenesis and/or spermiation in juvenile male sea bass. Furthermore, the profiles of these reproductive hormones were altered by both expanded and compressed photoperiods, and first sexual maturation was advanced by at least 2 months.

Effect of photoperiod manipulation on daily rhythms of melatonin and reproductive hormones in caged European sea bass (Dicentrarchus labrax)

There are few studies regarding the daily changes in reproductive hormone profiles in teleosts. The aim of the present research was to investigate the effects of photoperiod manipulation on daily rhythms of melatonin and reproductive hormones (pituitary and plasma LH, testosterone [T] and 11-ketotestosterone [11KT]) in juvenile sea bass, kept in net cages under farming conditions in winter. Our results provide the first evidence for the presence of daily variations in pituitary and plasma LH and plasma T in sea bass. Artificial lights suppressed circulating plasma melatonin levels and significantly affected the daily rhythm of LH storage and release.

Gene expression of estrogen receptors α and β during early sexual differentiation in the European sea bass (Dicentrarchus labrax)

A dimorphic expression pattern of ERα was found during sexual development in the European sea bass. It is therefore suggested that ERα plays an important role in sexual differentiation in this species.