By George Munene
Catfish culture in concrete greenhouse ponds is a new innovative alternative to use of outdoor pond liners that helps to curb cannibalism which eats into up to 42 per cent of the profits of catfish farmers. The warm weather inside the greenhouses also encourages faster growth of the fish. Concrete ponds are also more durable, lasting for over 20 years if made from quality material.
Anthony Mwangi, the proprietor of Oasis Aquafish Farm in Thika explains that one of the major challenges faced by catfish farmers in Kenya is the cannibalistic nature of the species. According to a study of the effects of catfish grading in Kenya done at Mwea Aquafish Farm Limited by the Journal of Aquaculture, Fisheries & Fish Science: fish graded every two weeks had a 7.5 per cent cannibalism mortality rate compared to 42.4 per cent in fish that were not graded and 18.9 percent for fish graded every four weeks. Size variation was also significantly affected by grading frequency with fish graded every two weeks gaining and retaining weigh quicker followed by those graded every four weeks and finally those with no grading treatment being the lowest.
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Concrete greenhouse ponds measure just 3 x 4 meters; this makes management easier for the farmer as they are able to prevent cannibalism in their stock by regularly sorting the shooters (fast maturers) and removing them before automatically refilling the pond with water. Concrete ponds are recommended to house hardy fish species like catfish, which can survive at a high stocking density. With a stocking rate of 100 fish per square meter, the pond can fit 1000 fish. Utilising best management practices, a farmer can harvest up to one tonne of fish in 9 months from the 3*4 metre pond.
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From Mwangi’s experience, due to the water in the pond averaging a constant 35°C, fish reared in concrete greenhouses reach one kilogram (plate size) faster than those stocked in outdoor ponds. Pond liners also start to fray and need replacing after three to four years while concrete ponds last for over 20 years without needing much refur
Depending on the availability of materials used in its construction, a concrete 12 square meter greenhouse costs between Sh 50,000 and 80,000.
Anthony Mwangi: 0721847378