The natural fish harvest has declined during the last 10 years in Cambodia due to illegal fishing and environmental changes. This has a significant affect on the livelihood of Cambodian people whose main protein source is deriving from fish. At present, much effort from government, development institutions and the private sector has been given to the development of aquaculture in order to match the shortfall of fish protein fish human consumption. It has been observed that around Phnom Penh city and else where with access to water and ponds fish culture has increased. Farming of common carp, silver carp, silver barb, tilapia and catfish is encouraged by government and development organizations so that farmers in the rural area can have fish for their own consumption and income generation.
Fish culture in the rice field is especially interesting as a method for maximizing land use, combining the production of both rice and fish. Fish culture in the rice fields is mainly concentrated in Southeast Asia where it has been known for centuries. A number of advantages are obtained by applying the rice-fish cultivation. The presence of fish in a rice field generally increases the rice yield by 10 to 15% (Hilbrands et al 2004). Fish is a source of protein and by integrating production with rice food security is improved. In addition, raising fish contributes to the improvement of public health because they can eat insects like mosquitoes. Raising fish in a rice field is also a biological way of reducing weeds, insects, snails and some rice diseases. This is a safe and cheap alternative to using chemical pesticides to control insects and algae. In areas where rice production is not profitable in all seasons, fish production forms an alternative source of income from the field (Hilbrands et al 2004).
The major factors that influence the economics of fresh water fish production in pond culture are:
fertilization of the ponds in order to increase the feed available in the natural stimulating the natural food web food chain;
supplementation with commercial fish pellets or with local feed resource; and
stocking density of the fish in the pond
When fish are raised in the rice field, the same factors apply but in addition there are the direct and indirect effects of the fish on the yield of rice.
The aims of the experiments reported in this thesis were:
To study the effect of stocking density and fertilization on the growth performance of tilapia raised in ponds supplemented with water spinach and duckweed
· To study the effect of stocking density and supplementation on the growth performance of tilapia raised in rice paddies .