Grow-out of Murrels (snakeheads)

Grow-out

For monoculture as practised in Thailand and Hong Kong, shallow ponds of a surface area of 800 m² to 0.5 ha are used. Where intensive farming is undertaken, a continuous flow of water or frequent exchange of water is maintained. The usual pond preparation including draining, liming and drying of the pond bottom is necessary. Thai farmers stock 75–460 fry of C. striatus per square metre of pond area.Stocking is carried out in the months of July/ August in order to harvest market-sized fish in April/May of the following year. The supply from capture fisheries is low during this period and so the fish can be sold at a high price. Trash fish, rice bran and broken rice are fed thrice daily in the ratio of 8 : 1 : 1. The ratio of trash fish may sometimes be raised to 13. The fish grow to market size in seven to eight months.

In cage culture of C. micropeltes and C. striatus in Kampuchea, a stocking rate of 6000–10 000 fry is common in cages measuring about 625 m³. Fed on various types of vegetables (cooked pumpkin, banana, rice and rice bran) and animal products (including live and dead fish), they are reported to reach a weight of 1.5–2.5 kg in nine months. In Vietnam, where cage culture of the above two species is practised, cages of about 125 m³ are stocked with 4–6 cm long fry collected from the wild, at the rate of about 80 per m³. Harvesting is carried out after about nine months of culture, as in Kampuchea.

In polyculture with Chinese carp in Taiwan, ponds are stocked with fingerlings of about 10 cm at a rate not exceeding 500/ha. When cultured with tilapia, the recommended stocking rate is about 90 000 10 cm fingerlings/ha. In polyculture with Chinese carps, the murrel (C.maculatus) feed on weed-fish, and in culturewith tilapia the fry produced by wild spawning of tilapia forms the main source of food. In order to avoid cannibalism, the stock of murrels is graded two or three times during the culture period, reducing the stock density finally to 15 000–24 000/ha.

Though there are several records of parasite infestation of murrels, serious outbreaks of disease or mortality are not as common.

However, in the intensive murrel culture in Thailand, mortalities occur more frequently. The farmers try to control this by providing feed containing antibiotics, even though the actual cause of mortality is not known. Fry of C. micropeltes and C. striatus have been foundto be very susceptible to ectoparasites, such as Costia spp., Chilodonella spp. and Trichodina spp.; Ichthyophthirius multifiliis has also been recorded from these species. Gill rot caused by Branchiomyces sanguinis has been identifiedin C. marulius, and infection by the fungus Dictyuchus anomalous causes mortality of C. punctatus.

Harvesting of murrels from ponds is achieved by draining and seining. The yield in Thailand is reported to be up to 25 kg/m². Catches are sold in live condition as the price of dead fish is usually 30–40 per cent less than that of live fish. In some areas in Thailand, murrels are salted and dried, and poor-quality fish are processed by fermentation. Though feeding is a relatively major cost of production, murrel culture has proved to be very profitable in all Asian countries, because of the high price in the markets. Available data on cost and earnings show 25–67 per cent net income on total operational cost.