Induced spawning in common sole (Solea solea L.)

In Europe, the soles Solea solea (Linnaeus 1758) and Solea senegalensis (Kaup 1858) are considered among the most promising species for marine fish farming. Several studies conducted from the 1970s to develop the production technology of these species suggested simple schedules to obtain spontaneous spawning. Despite these results and available technical information, nowadays, sole production is still at the pilot scale as breeders in captivity perform poorly or fail to spawn. Moreover, for mass production essential knowledge of some reproductive traits, such as ovulatory period, spawn frequency, egg production and male fertility, is still scarce. With the aimof producing juveniles to supplement natural recruitment, a broodstock of S. solea was adapted to captivity and induced to reproduce. The present study reports the results of 5 years of experiments. Sole breeders studied herein spontaneously spawned within the first year of captivity and eventually spawned inthe following year. However, in contrast to that reported by other authors, prolonged captivity apparently inhibited egg release. When egg release was inhibited in the stock tank, it always started inthe experimental groups just after administration of long-acting GnRHa yielding productions comparable with spontaneous spawning, although concentrated in a shorter period. The effectiveness of long-acting GnRHa is further highlighted by comparison with data on egg production reported in the literature for soles spontaneously spawning (range 3000^240 000 embryos per kg BW per season) as well as in short-acting LHRHa-induced females. Apart from hormonal treatment, other parameters such as diet andwater temperature are of paramount importance in promoting proper gonadal development and spawning in captive soles.