A comparison of fertilization, feeding and three periphyton substrates for increasing fish production in freshwater pond aquaculture in Bangladesh

A polyculture trial was conducted in earthen ponds in Bangladesh to compare traditional aquaculture techniques (fertilization only or fertilization plus feeding) with a combination of the same techniques and periphyton substrates. Three substrates (bamboo, jutestick and bamboo side shoot) were tested. Rohu (Labeo rohita), catla (Catla catla) and kalbaush (L. calbasu) were stocked at a 60:40:15 stocking ratio and at a total stocking density of 11,500 per hectare in 15 earthen ponds with five treatments: standard fertilization as input (Control), control plus supplemental feeding with rice bran and oil cake (Feed), control plus bamboo substrate (Bamboo), control plus jutestick substrate (Jutestick) and control plus bamboo side shoot substrate (Kanchi). Water quality, plankton and periphyton were monitored throughout the experiment. Significantly higher ammonia concentrations were recorded in Control and Feed treatments. The chlorophyll a concentration of pond water was significantly higher in the Feed treatment than in the Jutestick treatment. Dry matter content and mean abundance of the periphyton communities were higher in the first and the last month of the experiment without significant difference among the three substrate types. Periphyton chlorophyll a concentrations per unit surface area did not vary significantly among different substrate types but increased throughout the experimental period and decreased with increasing water depth. Specific growth rates of rohu and catla were higher in Substrate and Feed treatments than in the Control treatment. Combined net yields of fish in Control, Feed, Bamboo, Jutestick and Kanchi treatments were 1226, 1960, 2098, 2048 and 2032 kg ha(-1) 135 day(-1), respectively. Production in substrate systems was significantly higher (ANOVA, P<0.001) than in the Feed and Control treatments. Nitrogen retentions in fish in the Substrate treatments were 1.6 times higher than in the Control treatment and 1.3 times higher than in the Feed treatment. Net profit margin was highest in Jutestick treatment (46%). The substrate-based systems performed better than the conventional systems, both from ecological and economical points of view.