CHAPTER VI
EGG COLLECTION
Abalones hold matured eggs for 3–6 months. They can be spawned and artificially collected using various external stimuli. Physicochemical and biological stimulation are widely used.
6.1 Ultraviolet method
Male and female specimens are separated prior to their spawning. This method exposes gravid individuals, which are kept in the dark, to flowing and heated seawater previously irradiated with ultraviolet light. After two or three hours the male or female abalones will start to release their gametes. This method is extremely useful in commercial scale establishments as it is possible to obtain a high spawning rate, large number of eggs, and higher fertilization rate. This method is usually successful with fully matured abalone specimens. The intensity required for irradiating the seawater flowing through the UV lamp sterilizer varies with water clearness, however one twentieth (1/20) of the nominal sterilization capacity is usually sufficient.
6.2 Desiccation method
After exposing mature individuals to air for about 30 minutes or 1 hour, they are placed into the egg collecting tanks. Filtered seawater is added into the tanks which are kept in a dark room. Spawning of eggs and sperm is usually successful if the spawners are fully mature.
6.3 Thermal shock method
This method raises the ambient seawater temperature to 27 °C for 30–60 minutes and lowers it again to the ambient temperature. Several temperature cycles are usually sufficient to induce spawning in mature individuals.
6.4 Other method
Other methods used to artificially induce spawning are: injecting 2–4 cc of either 3.7 % calcium chloride solution into the mature abalone or sterilized and filtered seawater into the head, intestine ganglion and/or foot ganglion.
6.5 Combination method
This method is to induce spawning by placing adult abalones that have already been given the dry stimulus treatment into seawater which has been exposed to UV rays and with a controlled temperature.
If the eggs and sperm are released from the respiratory pore and spread out evenly, the induction is considered to be successful Following spawning the quality of the gametes should be carefully examined. Fertilization follows if the gametes are viable and of good quality.
CHAPTER VII
FERTILIZATION AND EGG WASHING
7.1 Egg fertilization
The spermatozoan of abalone are active for 24 hours, however fertilization of eggs should be effected within one hour from spawning. Concentration of released sperm should be measured on the haemocytometer and the amount of sperm necessary for fertilization should be determined. About 1500–4000 eggs per litre and about 10,000 spermatozoan per egg should be put into filtered seawater and well mixed. Polyspermy is caused by an overabundance of spermatozoa. On the other hand, lack of spermatozoa leads to a low fertilization rate.
Egg washing is done by decantation, and the upper water layer of the tank is drained off to get rid of unfertilized gametes. This process is repeated several times. It is important to maintain a constant temperature throughout the washing process. Newly hatched larvae should be moved to a new tank.