With the objective of reducing pollution and increasing production efficiency in aquaculture in the Mekong Delta, a trial on aquaponic culture was implemented in which waste water from fish culture was used to grow vegetables. The trial was conducted in a system where broad head catfish (Clarias macrocephalus) was cultured in a recirculation system connected to the cultivation systems of 4 types of vegetable including watercress (Nasturtium officinale), Japanese parsley (Oenanthe javanica), water spinach (Ipomoea aquatica) and elongated mustard (Brassica integrifolia). Two experiments were implemented to find the most suitable vegetable for aquaponic culture and the best cultivation area of vegetable in aquaponic culture system. In the first experiment, broad head catfish with an individual weight of 30-50g were cultured at density of 200 inds.m^-3 in 4 of 1m³ tank designed in a recirculation system (Fig. 1) where the flow was maintained at a rate of 20 m³.day^-1. Fish were fed 3 times per day to access with 40% protein pellet feed. The fish tanks were connected to the system where 4 types of vegetables were cultivated at 100 inds.m^-2. A total of 8 m² of vegetable cultivation area was made by PVC tube (Æ60 mm) system (Fig. 2). In the second experiment, the best grown vegetable was selected to test the nutrition provision capacity from the fish culture system. Different cultivation area of vegetable was applied including 2, 4 and 8 m² to receive and assess nutrient supply capacity from a 4 m³ tank fish system. Fish were bigger in size (100-150g.ind^-1) were stocked at density of 100 inds.m^-3 in 4 of 1 m³ tanks. Feeding regime was maintained similarly to the first experiment. Waste water from the fish tanks was discharged into the vegetable cultivation system. In both experiments, growth of fish and plants were monitored monthly. Survival rates of fish and plants were recorded at the end of the experiments. Water parameters, especially N-NH₄⁺, N-NO₃^-, P-PO₄^3-, TN và TP were measured before operation of the system and followed up weekly. The nitrate contents in the vegetable was also measured at the end.

The results showed that four kinds of vegetable grew well in the experimental systems, however, elongated mustard was the best with highest survival (>95%) and harvestable size rate (>90%). The best ratio between fish culture volume and vegetable cultivation area was 4 m³ to 8 m² equivalent to 1 m³ of broad head catfish used for 2 m² of elongated mustard. In both experiments, with high growth rate (>0.7%/day) and survival (>93%), the broad head catfish indicated that they can grow well in the recirculation system which can be applied to produce marketable size of highly economical valuable species (like this species) and simultaneously biomass of vegetable, and importantly minimize pollution caused by fish culture. This aquaponics system could be disseminated and applied to different conditions with other species in the Mekong Delta.