Development of low cost weed based aquaculture technology in ponds

Abstract

Three experiments were conducted during 2010-2012 towards the development of low cost weed based aquaculture technology in ponds. Experimental ponds were located at Kushtia district, Bangladesh. In experiment-1, six different conventional and non-conventional fish feed items like rice bran, wheat bran, mustard oilcake, Azolla, grass and banana leaves were tested to determine the nutrient contents (protein, lipid and carbohydrate) under 6 treatments as T1, T2, T3, T4, T5 and T6, respectively. Considering the nutrient content in experiment-1, experiment-2 evaluated the fish production and economics under 4 treatments of feed and weed based system with a similar stocking density of 11115 fish/ha in polyculture ponds as T0: ponds fed with conventional feed like rice bran, wheat bran and mustard oilcake (no weed was used as fish feed), T1: Azolla (Azolla pinnata) fed ponds, T2: Grass (Cynodon dactylon) fed ponds and T3: Banana (Musa acuminata) leaf fed ponds. Based on the performance of weeds and feeds in experiment-2, experiment-3 optimized the stocking density for Azolla based carp polyculture system in ponds under 3 different treatments of stocking densities like T1: 9880 fish/ha, T2: 11115 fish/ha and T3: 12350 fish/ha. Nutrients in weeds and feeds were compared for a period of 6 months (April to September) in experiment-1. Fishes (Hypophthalmichthyes molitrix, Catla catla, Labeo rohita, Cirrhinus cirrhosus, Cyprinus carpio, Ctenopharyngodon idella and Barbonymus gonionotus) were also grown for a period of 6 months (April to September) in experiment-2 and experiment-3. Mean initial stocking weight of H. molitrix, C. catla, L. rohita, C. cirrhosus, C. carpio, C. idella and B. gonionotus were 62, 64, 57, 54, 63, 65 and 25 g, respectively for experiment-2 and 60, 65, 58, 52, 61, 70 and 22 g, respectively for experiment-3. There were 3 replications for each treatment under different experiments. Liming (250 kg/ha) and basal fertilization (cowdung: 1500 kg/ha, urea: 60 kg/ha and TSP: 60 kg/ha) were done for all the treatments under experiment-2 and experiment-3. Urea (2.5 kg/ha/day in all treatments except treatment T1 under experiment-2 and in no treatment under experiment-3) and TSP (2.5 kg/ha/day in all treatments under experiment-2 and experiment-3) were applied as periodic fertilization. In case of experiment-1, nutrient contents (protein, lipid and carbohydrate) were monitored monthly whereas in case of experiment-2 and experiment-3, water quality parameters (water temperature, transparency, DO, pH, alkalinity and free CO2) were monitored fortnightly and fish growth parameters (weight gain and SGR) were monitored monthly. Economics (in terms of total cost, gross benefit, net profit margin and CBR) of fish farming were also evaluated for both experiment-2 and experiment-3. In experiment-1, significant variations (P<0.05) were found in the mean values of nutrient contents with different treatments of feed items but in case of same feed item no significant difference was found in the nutrient content at different months. Among the non-conventional feed items treatment T4 (Azolla) varied more significantly (P<0.05) for the mean values of protein content. In experiment-2, no significant differences in the mean values of water quality parameters were found among the treatments. Treatment T0 varied more significantly (P<0.05) for the mean values of SGR, weight gain, final weight, survival rate and total yield but in terms of total cost, gross benefit, net benefit, net profit margin and CBR, treatment T1 (Azolla fed pond) was found best. In experiment-3, no significant differences in the mean values of water quality parameters were found among the treatments. Significant difference (P<0.05) with the treatments were found in all the growth parameters except survival rate. Treatment T3 varied more significantly (P<0.05) for the mean values of total yield but in terms of total cost, gross benefit, net benefit, net profit margin and CBR, treatment T1 (stocking density of 9880 fish/ha) was found best. Findings indicated that the stocking density of 9880 fish/ha could be a good option for low cost Azolla based fish farming in Bangladesh.