Synchronous gamete maturation and reliable spawning induction method in holothurians

Several years of research on the gametic development and spawning of different species of holothurians have produced results that find applications in aquaculture and fisheries management programs. The first set of data shows that sea cucumbers secrete a biologically active chemical which allows gamete synthesis synchrony among conspecifics. Laboratory experiments have revealed that the gametic development was significantly less synchronous among individuals that were maintained separately under natural environmental conditions than it was among similarly treated individuals kept in groups. Furthermore, the presence of mature individuals was found to induce the gametic development of less mature ones. The active substance is present in the mucus secreted by the body wall enabling it to travel fair distances, although transmission is often favoured by pairing and aggregative behaviours. These findings indicate that the lunar cycle, photoperiod, food supply and temperature cannot individually account for the onset and synchronization of reproduction, but rather that environmental cues act synergistically and can be transmitted within and between populations through chemical communication. This has repercussions on both fisheries and aquaculture techniques. Preserving untouched populations while fishing intensively on other grounds should be favoured compared to steadily lessening the biomass, whereas broodstock should be maintained in a way that promotes interactions long before the breeding period. The other aspect of the study arose from the fact that holothurians are among the most commercially valuable echinoderms for which successful spawning induction is still difficult to obtain on a reliable basis. Recent results show that the transfer of perivisceral coelomic fluid (PCF) can be used as a reliable tool to induce spawning in mature individuals. PCF collected from individuals that had been in the typical spawning posture for about 20 min, without shedding gametes, triggered spawning in 71-100 % of conspecifics. The individuals responded to the injection of a 23 ml aliquot by displaying the spawning posture within 30-62 min, followed by massive gamete broadcast 57-83 min later. The results varied according to the time of PCF collection with respect to the spawning activity of the donor and the amount of PCF injected. The triggering substance was found not to be sex-specific since positive responses were observed in individuals of the same or opposite sex as the donor. Thus, PCF collected from early spawners can be used to spread and maximize spawning among the entire broodstock.