Development and performance evaluation of sludge remover for intensive aquaculture

Abstract

Fishery is an emerging sector in Bangladesh producing about 3.50 million tons of fish annually of which aquaculture accounts for 2.00 million tons. In intensive aquaculture, pond water gets polluted due to high stocking density and large amount of supplemental feeding results in huge accumulation of unused feed and faeces in the pond bottom. The accumulated bottom sludge depletes dissolved oxygen (DO) and releases harmful gases due to excessive use of chemicals and lack of water exchange facilities. These have negative impact on fish production and economic performance, through disease outbreak, mortality, poor feed conversion ratio (FCR), specific growth rate (SGR) and bad odor in fish muscles. This study was undertaken to develop a sludge remover for cleaning sludge from the intensive fish farming pond and to find the impact of sludge removal on water quality and growth of fish. A sludge remover was developed in Bangladesh Agricultural Research Institute (BARI) which is capable of removing sludge up to 40–50mm from the pond bottom. The main components of sludge remover are a float, axial flow pump (102mm diameter), 7.50kW diesel engine, sludge sucker, crane, propeller, rudder, etc. The discharge of the sludge pump was 14.11L/s. The effective field capacity and field efficiency were 0.078ha/h and 77.23% respectively at the forward speed of 12.5±1.55m/min. The water and sludge ratio was 3.6:1.0 (weight basis). A field trial was carried out to determine the effect of sludge removal on water quality and growth of fishes in intensive cultured ponds. Sludge was removed at three months interval from three pangus-tilapia-carp polyculture ponds. Three ponds of same size and fish stocking were kept as control. Water quality parameters like DO, pH, transparency and, unionized ammonia significantly (p≤0.05) improved in the sludge removed ponds compare to control ponds. Sludge removed ponds demonstrated better FCR (1.64) and SGR (0.80% per day) compare to FCR (1.90) and SGR (0.71% per day) of control ponds. Fish survival, net yield, net return and BCR (5.40) of sludge removed ponds were higher than those of control ponds. This sludge remover may be recommended for cleaning sludge from intensive cultured fish ponds.