Shellfish Breeding and Hatchery Management (2+1)

22.3.2 Induced Spawning & Fertilization

Spawning Inducement
Thermal stimulation
Best results for thermal stimulation were obtained only during the breeding peaks (March-May) of the sea cucumbers. The temperature of the water was raised by 3-5 °C by slowly adding hot seawater and stirring uniformly. Usually 20 specimens were introduced into the tanks at 10:00 hrs. By 13:00 hrs the males had released sperm by raising the anterior end . One hour or so after the males had released sperm, the females started releasing the oocytes. Simultaneously, several males in the tank were still releasing sperm. It is better to keep only one male spawning in the tank, otherwise the over-abundance of spermatozoa clouds the water.
Spawning behaviour
In sea cucumbers the sexes are separate but it is not possible to separate the males and females from an external examination in most species. In the case of H. scabra, only a microscopic examination of the gonads reveals whether the specimen is a male or a female. However, it is possible to distinguish them at the time of spawning since the spawning behaviour of the males and females is different. Typically, males spawn first, followed by females. The male first lifts the anterior end and exhibits swaying movements just like a snake. After exhibiting such movements for some time the males start releasing the sperm in a fine white stream from the gonopore situated at the anterior end and in the mid-dorsal position. When a male starts releasing the sperms it continues for nearly 2 hours. Meanwhile the ripe females start reacting, possibly to the presence of sperm released in the water. The anterior ends of females become bulged due to the pressure created inside the gonopore by the accumulation of oocytes. The female releases the oocytes which settle down on the bottom of the tank. Sometimes the same females spawn for a second or even third time; this is mainly observed in large specimens. The oocytes are ejected out through the single gonopore. They are ejected out in a powerful jet reaching a distance of about one metre, helping in the dispersal over a wide area. The gametes are released as a light yellow mucus-like substance.