Nguyen Huu Yen Nhi
Faculty of Agricultural and Natural resource, An Giang University, Long Xuyen City, Vietnam
Aquaculture is the growing of aquatic plants or animals for all or part of their life cycles. Primarily, its role is to produce food for human consumption, but it also has other purposes such as ornamental uses and as an aquarium. According to FAO (2008) the total aquaculture production of the world in 2006 reached 51.7 million tonnes including 31.6 million tonnes from inland fisheries. The demand is expected to increase every year and so aquaculture will become increasingly important in the future. The practice of aquaculture in inland fisheries is by many methods, but most effort is directed to intensive systems. In the past, farmers used the trash fish from inland and coastal water bodies to feed fish which have high economic value. However, the availability of trash fish is decreasing (Supis Thongrod 2005) so the farmers are finding and using other sources of animal protein like earthworms, which can be produced from organic wastes (Edwards et al 1998).
Presently aquaculture is economically a very important sector in Vietnam. Some species of fish like Marble goby and Catfish have an especially high value. Marble goby (Oxyeleotris marmorata Bleeker) is commonly cultured in cages in rivers and reservoirs, ponds and coves in Vietnam (Vu Cam Luong et al 2005). This species is considered as a delicacy in some Asian countries and fetches a high price (> US$17/kg) because of its tender meat and tasty flavor (Cheah et al 1994). Marble goby culture has been developed in ponds and coves since early 2000 (Vu Cam Luong et al 2005). However, lately marble goby culture has decreased due mainly to lack of seed supply and disease outbreaks, with especially high mortality during the larval stages, which is the major problem in mass production of this species. Marble goby is a sit-and-wait predator. However, its feeding behavior has not been fully understood, especially at the young stage. Marble goby larvae that prey on live food had better survival rate and growth rate than larvae fed with artificial feed (Cheah et al 1994). The use of live feed for nursing fingerlings might be a better way to improve seed production. It is important to understand appropriate feeding strategies for marble goby during fingerling stages. Therefore, it is necessary to study the feeding behavior of young marble goby on various live feeds which could be mixed with rice bran. This understanding will provide the basic knowledge to supply live feed to Marble goby during young stages. A successful nursing technique to supply Marble goby seed to farmers would help to conserve natural stocks and enhance marble goby culture in the region.
Tra catfish (Pangasius hypophthalmus), a member of the Family Pangasidae, also has high economic value, and has become one of the most important species in Vietnam and other countries in the South East Asia region. This fish is raised in ponds, cages and fence culture (Chau Thi Da et al 2007). However, farmers have changed from the cage to pond culture because the cost of the cage system is higher and the fish easily get diseased. The fingerlings of Pangasius hypophthalmus are almost entirely produced by artificial rearing because the natural fingerling yield from the Mekong River has been reduced (Van Zalinge et al 2002).
The earthworm Perionyx excavatus is the most common species in Vietnam. It plays a major role in waste management by converting large amounts of organic matter into rich humus, and thus improving soil fertility. This is achieved by the worm's action of ingesting organic matter deposited on the soil surface, especially manure, which it utilizes as food. Earthworms grow very well on manure, especially that from goats (Nguyen Hieu Phuong 2008). Earthworms have high protein content with a well-balanced array of essential amino acids. http://www.earthwormvietnam.com/Eng/powdereng.htm.
For this reason, earthworms have been shown to be an important feed resource for raising fish (Nguyen Duy Quynh Tram et al 2005) and frogs (Latsamy Phounvisouk and Preston 2007). Earthworms offer flexibility since the farmer can raise then without depending on the season, in contrast with freshwater trash fish which are most common in the flood season.
There is a need to develop systems for the production of worms for aquaculture. Earthworms could have a special role in intensive aquaculture industries, especially in raising Marble goby, which can be raised more easily when given live food in the early fingerling stage.
The experiments were conducted to:
Record the growth of earthworms raised on manure from cattle or buffaloes with and without addition of water hyacinth
Study the growth and survival rate of fingerling Marble goby and Tra catfish when fed earthworms, as compared with the traditional feeds of trash fish and rice field prawns.