Coastal Aquaculture and Mariculture (2+1)

Unit 1 - Shore based aquaculture and mariculture

1.2.4.1. Molluscs - major producers

China and Japan are the largest producers of cultured scallops, with the bulk of production being the yesso scallop (Pecten yessoensis). Production in 2003 exceeded 1.1 million tonnes of yesso scallop. Preferred harvest size (>10 cm shell length) is reached in 2–3 years. Giant clams (Family Tridacnidae) have been cultured in many Pacific Island countries. Their relatively slow growth rates make tridacnid clams suitable only for extensive aquaculture or stock enhancement. Much of the tridacnid aquaculture production is sold to the marine ornamental market, which provides higher and more rapid returns.

 

Pearl oysters are farmed in Japan, China, Australia, Indonesia and in several Pacific Island nations, notably French Polynesia and the Cook Islands. Pearl culture is technically intensive, particularly the process of inserting a nucleus to promote formation of a pearl. The period between nucleus insertion and harvest generally ranges between nine months and three years. The quality of the pearl is related to the length of the culture period, but many insertions are unsuccessful, resulting in the death of the pearl oyster or ejection of the nucleus. Pearl oysters are usually grown out using suspended culture systems in which oysters are usually suspended below rafts or on long-lines.

Due to their filter-feeding nature and the environments in which they are grown,edible bivalves are subject to a range of human health concerns, including accumulation of heavy metals, retention of human health bacterial and viral pathogens, and accumulation of toxins responsible for a range of shellfish poisoning syndromes. One option to improve the product quality of bivalves is depuration, which is commonly practiced with temperate mussels, but rarely used in the tropics. A major constraint to the development of tropical mussel culture is limited demand and low price. Although prices are higher in Australia and New Zealand, mussels are still relatively low-priced compared with other seafood commodities. The low economic value of mussels is compensated for by their ease of culture and high productivity. Bioeconomic evaluations of mussel culture in the Philippines indicated a low return on investment for mussel farming, although farming in Thailand and Malaysia compared favourably with other forms of aquaculture.