Long photoperiod on sea cages delays timing of first spermiation and enhances growth in male European sea bass (Dicentrarchus labrax)

26 p., il. y bibliografíaTwo large groups of fingerling (3.2 g) male European sea bass (around 75,000 individuals each) reared in net sea cages for a period of two years were exposed to two different photoperiods starting in June: either ambient photoperiod (37º 24′ N) (NP) or a constant long photoperiod (LP; 18 h light: 6 h dark, 18 L: 6D). Long days had limited effect on somatic growth at the time of incipient gonad development (IGD, 1st annual cycle; November–March), while they were effective at the time of full gonad development (FGD, 2nd annual cycle). Moreover, the annual patterns of morphological indices, i.e., Fulton's condition factor (CF), visceral fat index (VFI) and particularly gonadosomatic index (GSI), were delayed by one or two months as the result of the long days compared to the control group (NP). LP did not prevent the onset of puberty but delayed spermiation by one month, and modified accordingly the phase and/or amplitude of the annual rhythms of pituitary gonadotropin releasing hormone (sbGnRH) content and plasma levels of luteinising hormone (LH) and sex steroids, particularly that of 11-ketotestosterone (11-KT). In general, high levels of sbGnRH (≥4 ng/pit) were associated with elevated plasma LH (1–3 ng/ml at IGD and ≥8 ng/ml at FGD), and the sex steroid peaks usually preceded LH peak in both treatments (1–2 months earlier). Finally, full spermiation and the maximum GSI values coincided with the LH peak, highlighting the close relationship that exists between LH plasma levels and gonadal development.This research was supported by MCYT grant No. 1FD1997-1699-CO2-02/MAR to SZ, and by Generalitat Valenciana Grupos 04/80 to MC; I. Begtashi was funded by an AECI grant.Peer reviewe

Development and validation of an enzyme immunoassay for testosterone: Effects of photoperiod on plasma testosterone levels and gonadal development in male sea bass (Dicentrarchus labrax, L.) at puberty

A specific immunoassay was developed for the quantification of testosterone (T) in sea bass plasma. Specific primary antibody against T was produced using an antigen BSA conjugated with T. The enzyme immunoassay (EIA) had a sensitivity of 5-0.009 ng ml-1 and 6.2% intra-assay variation; inter-assay variation was 9.5% for sea bass plasma. The effects of two different accelerating photoperiod regimes, compressed photoperiod (CO; 6 months), and constant short photoperiod (9L:15D) with a long photoperiod (15L:9D) in March (SLmar), on T plasma levels and sexual maturation were examined during the onset of puberty in male sea bass. Natural photoperiod (NP) and SLmar groups exhibited the highest T values in December (8.69±1.03 and 10.85±1.04 ng ml-1, respectively). However, SLmar group showed the first significant decrease in T plasma levels in January, two months earlier than the NP group, which presented elevated T levels until February. The CO group displayed two significant T peaks, one in October (8.90±1.60 ng ml-1) and the other in January (9.60±1.10 ng ml-1). Gonadosomatic index (GSI) in the NP and SLmar groups displayed the highest values from December to February (>2.5%). However, the SLmar group showed the first significant increase in GSI in November, one month before the controls, indicating a clear advancement of gonadal development with respect to the NP group. In the CO group, a bimodal pattern was observed with two peaks, one in October-November (1.30±0.25%) and the second in March-April (0.97±0.33%) (P<0.05). In NP group, the percentage of running males was about 80% from December to March while the percentage of running males in the SLmar group (∼70%) lasted only three months (December to February) decreasing (P<0.05) in March. In the CO group, spermiation began in October (60%), decreased during the next months, and increased again in March-April (30%) (P<0.05). These results indicate the advancement of puberty by either one or two months with respect to the control group in the SLmar and CO groups, respectively, and the presence of a second reproductive surge in the CO group. Collectively, these results suggest that exposure of fish to these photoperiod regimes may affect both the time of the onset of puberty and the pattern of gonadal development in prepuberal male sea bass.We would like to thanks to Dr J.M. Cerdá-Reverter for his valuable suggestions and technical comments on the manuscript; to Dr Evaristo Mañanós and Dra. Ana Gómez for their helpful assistance and to Dra. Lisa Ann Sorbera for revising the English. This work was supported by a CICYT grant MAR97-1883-EU to M. Carrillo. L. Rodríguez was supported by a grant of the Ministerio de Educación y Cienci

Long-term exposure to continuous light inhibits precocity in European male sea bass (Dicentrarchus labrax, L.): Hormonal aspects

The effect of long-term exposure to continuous light on the hormonal aspects of the reproductive axis was investigated in juvenile male sea bass (Dicentrarchus labrax, L.) during the first annual cycle. Four-month-old fish were exposed to a simulated natural photoperiod (NP) and a continuous light (24 h) regime (LL) under natural conditions of temperature (13.3-25.8°C). A dot-blot technique was used to analyse gonadotropin (the common glycoprotein α, GPα; the follicle stimulating hormone beta, FSHβ; and the luteinizing hormone beta, LHβ, subunits) mRNA levels in the pituitary during the experiment. A homologous ELISA was used to determine pituitary sea bream gonadotropin-releasing hormone (sbGnRH) and LH and plasma LH levels; gonadal and plasma sex steroids concentrations were determined by specific immunoassays. LL significantly inhibited the expression of all three gonadotropins subunits in the pituitary. However, no significant differences on plasma LH levels were observed between NP and LL groups throughout the period of the experience. Long-term exposure to LL regime was extremely effective in inhibiting gonadal growth and hence precocious maturation as well as the accumulation of Testosterone (T) and 11-ketotestosterone (11-KT) in the gonads compared to the control group. 11-KT plasma levels remained low and unchanged in the LL group during the study. This work describe important alterations of the endocrine system, particularly at the pituitary-gonad axis provoked by exposure to continuous illumination and discusses the mechanism by which precocity in male sea bass is generated.This research was funded by the MCYT Project No. 1FD97-1699-CO2-02/MAR to S. Zanuy and the EU Project No. QLRT-2001-01801 and MYCYT project No. AGL2002-12470-E to M. Carrillo. I. Begtashi was supported by an AECI grant. Authors thank J.M. Cerdá-Reverter and S. Halm for their helpful comments on the manuscript and S. Ibáñez for her assistance during the sampling and the technical analysis

Long-term exposure to continuous light inhibits precocity in juvenile male European sea bass (Dicentrarchus labrax, L.). I. Morphological aspects

The effect of long-term exposure to a continuous light photoperiod was investigated in juvenile male sea bass (Dicentrarchus labrax L.) during the first annual cycle. Four-month-old fish were exposed to a natural photoperiod (40°N) (NP) and 24 h continuous light (LL), for 12 consecutive months, under natural temperature conditions (13.3-25.1°C). Long term exposure to LL regime was highly effective for the inhibition of the gonadal development and consequently the prevention of precocious males. The NP group showed a steady increase in gonadosomatic index (GSI) values from December to a peak in January (1%), while the LL group had a similar pattern but it did not surpass the 0.2% GSI at the peak level. Similarly, the LL group exhibited mostly immature stages of germ cell development from December to March contrasting with the NP group, which presented more advanced stages of maturation at these times. The NP exhibited a high incidence of precocious fish (21.9%, 15% and 2.6% in February, March and April, respectively), while the LL regime dramatically reduced these percentages to 0%, 3.32% and 2.25%, in February, March and April, respectively. The exposure of LL provoked a significant reduction of the visceral fat (VFI) and hepatosomatic index (HSI) throughout the reproductive period, suggesting an accelerated consumption of the fat reserves of the fish with respect to the control group. However, the carcass index, which indicates the eviscerated weight of the fish, increased significantly (P<0.05) in the LL group compared with the NP group. Finally, the exposure to LL induced a significant (P<0.05) loss of weight and length with respect to the NP group. © 2004 Published by Elsevier B.V.This work was supported by a MCYT grant No. 1FD1997-1699-CO2-02/MAR to S. Zanuy and to a UE project No. QLRT-2001-01801 to M. Carrillo. I. Begtashi was supported by an AECI grant. Authors thank to J.M.Cerdá-Reverter and Alicia Felip Edo for his valuable comments to the ms and to S. Ibañez and J. Monfort for their help during the sampling and histological procedures

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

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.This work was supported by a CYCIT grant MAR97-1883UE and a FAIR grant CT96-1410 to M. Carrillo. L. Rodrı́guez was supported by a grant of the Ministerio de Educación y Ciencia and a Bancaja-CSIC grant.Peer reviewe

Avances en la regulación hormonal de la diferenciación sexual y de la pubertad de la lubina europea

Trabajo presentado en el 5º Congreso de la Asociación Ibérica de Endocrinología Comparada, celebrado en Faro (Portugal), del 8al 10 de septiembre de 2005En los teleósteos existen dos períodos críticos del proceso reproductor: 1) la época en que adquieren la capacidad de diferenciarse hacia uno u otro sexo, y 2) el período durante el cual pasan de juveniles inmaduros a adultos capaces de producir gametos por primera vez. Estos dos períodos, conocidos como diferenciación sexual y pubertad, respectivamente, ocurren en una época muy concreta de la vida característica de cada especie. Ambos procesos están regulados hormonalmente y son influenciados por el medio ambiente externo. Desgraciadamente, en los peces existen grandes lagunas en el conocimiento de la regulación hormonal de estos dos procesos. La posibilidad de generar, por selección de tamaños, poblaciones de un sexo determinado, desde etapas muy tempranas de la vida y la de inhibir el primer desarrollo gonadal, por aplicación de fotociclos, han permitido estudiar el eje cerebro-hipófisis-gónada de la lubina en circunstancias óptimas para esclarecer algunos de los mecanismos endocrinos asociados a estos periodos. Ello proporciona un recurso prometedor para abordar el estudio del control hormonal y ambiental de la diferenciación sexual y de la pubertad de los peces y aporta conocimientos fundamentales y de aplicación en acuicultura.Estos trabajos fueron financiados por los proyectos nacionales: 1FD1997- 1699-CO2-02/MAR; AGL2002-10024; AGL2002-12470-E y europeos: QLRT2001-01801, Q5R-2000-31365