Small Scale Cage Aquaculture in River Ecosystem: Species Suitability, Production and Environmental Carrying Capacity

Abstract

A three years research protocol was set for the study on “Small scale cage aquaculture in river ecosystem: species suitability, production and environmental carrying capacity” involving three separate experiments like experiment-1 conducted in September to December, 2008 with a view to determine the suitable species, experiment-2 conducted in September to December, 2009 with a view to optimize the stocking density and experiment-3 conducted in September to December, 2010 with a view to optimize the dietary protein level for cage aquaculture in river. The experiments were conducted in 1×1×1m3 cages in Mahananda river under Chapainawabganj district, Bangladesh. Experiment-1 was designed with 3 treatments of aquaculture species like T1 (Macrobrachium rosenbergii 200/m3 cage), T2 (Oreochromis niloticus 200/m3 cage) and T3 (Barbodes gonionotus 200/m3 cage). Experiment-2 was designed with 3 treatments of stocking densities like T1 (O. niloticus 200/m3 cage), T2 (O. niloticus 150/m3 cage) and T3 (O. niloticus 100/m3 cage). Experiment-3 was also designed with 3 treatments of dietary protein level like T1 (25% dietary protein feed), T2 (30% dietary protein feed) and T3 (35% dietary protein feed). Each treatment had three replications for all the experiments. The stocking weight of aquaculture species was 5.5 g in experiment-1, 41g in experiment-2 and 15g in experiment-3. Water quality parameters (Water temperature, transparency, dissolved oxygen, CO2, pH, hardness, alkalinity and NH3-N) were monitored fortnightly and the growth parameters were monitored monthly. Pellet feed was supplied twice daily at the rate of 10% of fish/prawn body weight at start and 5% at the end of the experiments. In case of experiment-1, mean values of water quality parameters were found with no significant difference with the treatments and were found within the suitable range. Treatment T2 varied more significantly (P<0.05) than that of others for the mean values of growth parameters (final weight, weight gain, SGR, survival rate and yield) and CBR. In case of experiment-2, only dissolved oxygen and NH3-N varied significantly (P<0.05) with the treatments. Growth parameters and CBR varied significantly (P<0.05) with the treatments. In spite of having highest yield, CBR was found lowest with treatment T1 (i.e. highest stocking density). Both moderate yield and CBR were found with treatment T2. In case of experiment-3, mean values of water quality parameters were found with no significant difference with the treatments and were found within the suitable range. Treatment T3 (35% dietary protein feed) varied more significantly (P<0.05) than that of others for the mean values of growth parameters (final weight, weight gain, SGR, survival rate and yield) and CBR. Findings indicated that tilapia with a stocking density of 150/m3 cage fed with 35% protein feed was the suitable technique for small scale cage farming in river. Further research is also recommended to explore the production and economics of tilapia farming in large scale in river ecosystem.