Non-invasive assessment of reproductive status and cycle of sex steroid levels in a captive wild broodstock of Senegalese sole Solea senegalensis (Kaup)

Abstract

Senegalese sole, Solea senegalensis, intensive culture is currently limited mainly due to the low control on reproduction in captivity. Comprehensive knowledge of reproductive biology and physiology for this species is needed in order to improve tank spawning success. This work describes for the first time the seasonal profiles of plasma levels of sex steroids (17β-estradiol, testosterone, 11-ketotestosterone, and 17,20β-dihydroxy-4-pregnen-3-one [17,20β-P]) in a S. senegalensis captive wild broodstock held under natural conditions, during two consecutive reproductive cycles. Changes in apparent maturation in females, dynamics of sperm release in males, and the condition factor ( K) were monitored. Six maturation stages were established for females according to apparent size of the ovary and external abdominal swelling: early, intermediate and final ovarian development (F2+, F3+ and F4+, respectively), and partially spawned, mid spawned and spawned out or regressed (F3−, F2−, and F1−, respectively). During summer, F1− and non-running males (NRM) were predominant in association with low K and plasma steroid levels. At the end of summer, a new cycle of gonadal development started, denoted by the increase in reproductive parameters ( K and steroid levels) and the appearance of F2+. By middle autumn, some females reached advanced maturation stages (F3+ and F4+) while the proportion of running males (RM) showed a maximum. An occasional spawning could be registered during this season (November 2002). Towards the end of winter and beginning of spring, ovarian development reached its maximum. At this point, the proportion of F3+, F4+ and RM, K (specially in females), and steroid concentrations were the highest in concordance with the starting of the main spawning period (lasting from January to June 2003 and from March to June 2004). Throughout this period, concomitantly with oocyte and sperm release, the proportion of F3−, F2−, F1− and NRM progressively increased, while steroid levels and K progressively declined (concentration of steroids could fluctuate under a decreasing trend). The relatively elevated levels of 17,20β-P correlating with some parts of the spawning periods makes it a candidate for the role of the maturation-inducing steroid in S. senegalensis. Seasonal variations of measured parameters were consistent with the reproductive cycle of this species in the wild, and comparable to those found in other asynchronous multi-spawning fish.