LONG-TERM GROWTH AND SURVIVAL OF HYBRID BEWEEN Haliotis discus hannai AND Haliotis discus discus

Abalone is considered an important commercial species in the shellfish aquaculture industry. Though it accounts for only 3% of the total volume of the farmed shellfish, the species occupies over the half of the total value.

However, over-crowding and prolonged farming activities have caused problems like eutrophication, higher mortality and genetically inferior hatchery stock. As these problems are gradually lowering the productivity, many abalone farmers are looking for ways to shorten rearing period and to improve hybrid seeds with faster growth to overcome mortality.

To develop a hybrid abalone species with faster growth, this study conducted hybridizations between cold water H. discus hannai and warm water H. discus discus to produce both hybrid and pure hatchery stock and then compared growth and survival between the hybrid and pure seeds which were reared in indoor tanks and then seawater cages.

A 250 day long culture in indoor tanks showed the fastest growth in the hybrid H. discus hannai ♀ × H. discus discus ♂ with 33.9 mm shell length and 4.3 g weight, which was followed by the hybrid H. discus hannai ♀ × H. discus hannai ♂. After the 250 day long culture in tanks, seeds with about 34 mm shell length were selected from the tanks and transferred to seawater cages to be reared for another 950 days. The sea cage culture also showed the highest growth in the hybrid H. discus hannai ♀ × H. discus discus ♂ with 88.6 mm shell length and 90.5 g weight. Survival rate of the pure H. discus hannai ♀ × H. discus hannai ♂, the hybrid H. discus hannai ♀ × H. discus discus ♂, the hybrid H. discus discus ♀ × H. discus hannai ♂, and the pure H. discus discus ♀ × H. discus discus ♂ during the 950 day cage culture was 38%, 39%, 31% and 24%, respectively, indicating the hybrid H. discus hannai ♀ × H. discus discus ♂ having the highest Survival rate. Mortality mostly occurred in newly stocked small juveniles in the seawater cages. In conclusion, the comparison of growth and mortality between the hybrid and pure seeds reared in land-based tanks and seawater cages demonstrated that the hybrid H. discus hannai ♀ × H. discus discus ♂ performed the best.