Effects of estuarine oyster, Crassostrea cuttackensis as the extractive species at varied densities on productivity and culture environment in brackishwater integrated multi-trophic aquaculture (BIMTA) system.

Abstract

ntegrated multi-trophic aquaculture (IMTA) involves incorporation of species from different trophic or nutri- tional levels in the same system to get better production based on mutual gain to the co-cultured species and improved ecosystem health. However, in brackishwater, very few trials on IMTA have been conducted so far with scarce information on the optimum density of extractive species like oyster and seaweed. Edible estuarine oyster, Crassostrea cuttackensis is abundantly available in the Sundarban. Being a filter-feeder, it can be used as an extractive species for organic matter removal in IMTA. Therefore, an experimental trial was conducted to assess the effect of different stocking densities of C. cuttackensis on performances of milkfish (Chanos chanos) and Pacific white-leg shrimp (Penaeus vannamei), and environmental remediation in an IMTA system. There were three densities of oyster, 0.6 (T1), 1.2 (T2), and 1.8 (T3) kg m-3 distributed to 1000 L FRP circular tanks containing milkfish (4.51 ± 0.05 g) and white-leg shrimp (4.50 ± 0.03 g) at 25 and 50 no. m-3 , respectively. Control tanks contained the same number of milkfish and shrimp with no oyster. All the three treatments and control had triplicate tanks. During the 60-day trial period, fish and shrimp were fed with a common diet containing 30% crude protein at 5% of biomass. Results showed that the highest growth of milkfish (24.66 ± 0.31 g) and shrimp (15.20 ± 0.17 g) was obtained in T3 (P < 0.05) compared to that of the control [13.97 ± 0.08 g (milkfish), 11.83 ± 0.13 g (shrimp)]. Apparent feed conversion ratio (AFCR) was the lowest in T3 (0.92 ± 0.01) (P < 0.05). Although, survival of milkfish did not vary, shrimp survival was the highest in T3. The inorganic nutrients (nitrogenous and phosphorus compounds) and particulate organic matter (POM) of water improved in all the IMTA treatments compared to the control. The number of total heterotrophic bacteria and Vibrio counts in tank water was significantly low in T3 (P < 0.05). The benefit-cost ratio in T3 was found to be 1.6 times higher than that of the control. This trial suggested that oyster, C. cuttackensis can act as an effective extractive species in IMTA system when stocked at a density of 1.8 kg m-3 Therefore, treatment T3 IMTA model proved to be more productive and had a successful bio-remediation effect on the environment.