Key techniques
Because wild-born aquarium fish are still relatively plentiful and cheap, there has been little research into assisted reproduction of clownfish. Domestic and foreign commercial fish fry companies only develop breeding and rearing techniques for high-demand, high-price species. Moreover, they consider the techniques they have developed to be trade secrets.
Ho needed help overcoming difficulties related to establishing mating pairs and increasing the frequency with which the fish lay eggs. With little information from commercial research and development publicly available, he had to rely entirely on fish breeding techniques EMBRC had developed over the years. His goal was to adapt these techniques to allow him to produce large volumes of clownfish fry.
The first step was getting males to mate with females. He found that they need a quiet environment where they will not be disturbed. Moreover, sea anemones and coral are also essential. "Each species of clownfish lives in symbiosis with a specific species of anemone," explains Ho. "For example, ocellaris clownfish live in symbiosis with only three species of anemone: Heteractis magnifica, Stichodactyla gigantea, and Stichodactyla mertensii."
Clownfish are sensitive and very territorial. Only three to five clownfish live in a given sea anemone, and there is no guarantee that they will pair up. If they take a dislike to one another, they are likely to fight over territory and end up injuring one another.
EMBRC researchers therefore placed each male-female pair in a tank of its own, ensuring that the pairs were together all the time and thereby increasing the odds of mating success.
The temperature and quality of the water in the "maternity ward" were also crucial. Researchers tested the effects of variables one by one. They discovered that when they controlled the pH and the concentrations of nitrous acid and ammonia, egg production was highest with nine to 12 hours per day of light at 20,000 lux, a water temperature of 26° to 28°C, and a salinity of 33-35 parts per thousand.
Researchers also observed that certain signs indicated when clownfish were preparing to breed for the first time.
On their first reproductive cycle, the female clownfish would first choose a spot on coral next to a sea anemone. They would then spend the two to three days prior to laying their eggs removing algae and sediments from the site, sometimes using their tails to sweep away small stones. This behavior was more frequent as laying approached, and stopped only when laying began. On subsequent reproductive cycles, the fish only exhibited this behavior for two to three hours prior to laying their eggs.
Relying on its previous experience hatching saltwater fish and on close observation, EMBRC worked out the keys to breeding in captivity in just six months, enabling it to increase the frequency with which its clownfish laid eggs from five or six times a year to more than 20.
Young clownfish can be packaged and sold at 60 days old, when they are about two centimeters in length.