4.1.3 Conditioning bivalves in the tropics

Mention was made earlier in this chapter of the habit of many tropical species to spawn intermittently throughout most of the year. This presents problems in obtaining sufficient numbers of larvae to support production requirements of hatcheries in tropical and sub-tropical climates.

When there is little variation in seawater temperature and food availability during the year, bivalves do not to have a quiescent period – as do temperate and cold water species – that triggers synchronicity in reproductive development within a stock. This cooler period can be provided in tropical hatcheries by holding stock in water chilled to between 5 and 10oC below ambient with an adequate food ration for a period of 4 to 6 weeks. After this period they are gradually warmed to ambient conditions when a greater percentage of adults will mature gametes synchronously. This is a similar approach in many ways to that described in section 4.1.2.5.

The technique has been used with the mangrove oyster, C. rhizophorae, in Cuba. Similar methodology has also been applied successfully in conditioning Pacific oysters, C. gigas, in parts of Brazil. The problem is somewhat different in the latter case. Pacific oysters (an introduced exotic species) grow extremely well in the more southerly states of the country but they do not undergo reproductive development to the extent that they will spawn.