Postlarvae (PL) of Macrobrachium rosenbergii (de Man 1879) were stocked at 1, 2, 3 and 4 PL m−2. Prawns were fed only pellets (P) and a combination of pellets and snail meat (PS) with three replications in 100 m2 plots in the rotational prawn–rice system. Water levels were 0.3–0.6 m in rice growing areas. The water temperatures at noon in the hot months were higher than the suitable range for prawns. The final mean weights of prawns in treatments 1, 2 and 3 PL m−2 were significantly higher than in treatment 4 PL m−2 (P<0.05). The yields from different density treatments ranged from 194±82 to 373±32 kg ha−1 and increased significantly with the increases in prawn densities (P<0.05). There was no significant difference between the two types of feed on production parameters (P>0.05). The total cost significantly increased at higher densities (P<0.05), but it was not different between feed types (P>0.05). Net profit and cost benefit ratio of treatment PS were significantly higher than in treatment P. In the present study, treatment 3 PL m−2 and treatment PS offered the optimal results.

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An eco-technological survey was conducted in the central freshwater region of the Mekong Delta (Vietnam) involving around 260 fish farming households with different types of farming systems. The survey was carried out during the dry season of 1996 to describe and analyse the present state, structure and functioning, as well as constraints to, and management options of, integrated fish farming systems. Systems for the survey were selected to represent as wide a spectrum of farming conditions as possible among the high variety and combination of integrated fish farming systems existing in the central region of the Mekong Delta. Two basic types of integration were selected for the survey: AC/VAC systems of fishpond-livestock with/without a vegetable and/or fruit-tree garden; and AR system of rice-fish. A non-integrated system, namely fish culture in ponds and/or garden canals, was also investigated. Farmer-managed trials were conducted on 25 selected farms during the culture period of 1997-98 to test improved technologies based on the results of the survey by partial modification of the limiting technological parameters and management methods.

The WES (West-East-South) Aquaculture Project of Can Tho University had the ultimate objective of assisting rural households in the Mekong Delta of Vietnam to improve and diversify production, nutrition and income sources through integration of aquaculture practices into their farming systems. The final stage of the project comprised different activities involving aquaculture extension for the development of aquaculture in the rural areas of the Delta. Several studies in this region have suggested that relatively small incremental changes to existing farming systems should be made, rather than attempting to introduce alien technologies which usually fail. Small-scale farmers were selected as the target group. The basic institutional infrastructure for extension in the region was available; but the efficiency of the national extension service was low due to limited funds, facilities and knowledge. The WES-Aquaculture Project applied a step by step approach during the implementation of the extension component, which included surveys of farming system and existing extension activities, training courses for both extension officers and farmers, and in the final stage farmer-managed on-farm trials. The procedure for farmer-managed trials was technical assistance through farm visits, training programmes, field school workshops and study tours, and also interest-free credit. The results from 25 farmer-managed trials demonstrated significant improvement of the productivity of various farming systems. The fish yield in rice-cum-fish systems increased from an average of 429 to 801 kg/ha-1/crop-1 (average increase 2.1 times) while the fish yield in pig-cum-fish systems increased from 3860 to 7592 kg/ha-1/crop-1 (average increase 2.6 times). The success of the farmer-managed trials indicates the potential for rural aquaculture in the Mekong Delta through appropriate extension activities.

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