engleski

BROODSTOCK CONDITIONING AND INDUCED SPAWNING OF THE WARTY VENUS Venus verrucosa UNDER FOUR DIFFERENT FEEDING REGIMES

The warty venus, Venus verrucosa, is considered to be a shellfish species of high market value in the Mediterranean area. It is also a species of high interest for cultivation because a successful technology for artificial spawning and larval rearing does not exist. Successful artificial spawning is influenced by the composition of microalgae diets that are provided during the period of conditioning. This paper compares the results of two methods of induced spawning of warty venus reared under four different feeding regimes. Broodstock of warty venus was established by collecting adult specimens from their natural environment in the beginning August. Shellfish were kept in controlled conditions within a close recirculation system. Four different feeding regimes were applied during a 2.5 month conditioning period. The first regime included feeding with the diatom Cylindrotheca closterium only, the second with the diatom Chaetoceros muelleri, the third with a combination of the flagellates Tetraselmis suecica, Isochrysis galbana (60% ) and C. closterium (40%), and the fourth with a combination of T. suecica, Isochrysis galbanan (60%) and C. muelleri (40%). The commonly used diatom C. muelleri was replaced in the 3rd regime with C. closterium because of its abundance in the area where the broodstock originated. The daily amount of feed was calculated at 3% of dry tissue weight of the shellfish (Helm et al., 2004). The gonadal development was determined weekly by taking a tissue smear, and condition index was calculated according to Mann (CI = weight of dry meet / weight of dry shell x 1000) at the beginning and at the end of the conditioning period. After gonadal maturation, thermal shock and serotonin administration were used for the stimulation of spawning. Results indicated that the third regime, using a combination of T. suecica, I. galbana and, C. closterium provided the best, but not a significantly different condition index (fig. 1). Spawning induced by temperature shock and by the administration of serotonin was successful only with populations in the 3rd and 4th feeding regimes. Successful spawning was obtained in 52% of broodstock treated by temperature shock, and 48% of broodstock treated with serotonin. There were no statistical differences in the number of spawning individuals among these two groups. It could be concluded that thermal shock and serotonin administration are both applicable for the induced spawning of warty venus. C. closterium could be used as a valuable feed ingredient during the conditioning of warty venus.

warty venus; Venus verrucosa; feeding

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