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

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