Effects of stocking density on water quality and growth of bighead catfish (Clarias macrocephalus) rearing in recirculation aquaculture system

Abstract

Aquaculture is among the fast growing industry in the world. The biggest challenges facing the sector are the environmental pollution, shortage of land, diseases control and producing free contaminated fish. The present study evaluated the influence of stocking density on water quality and growth performance of bighead catfish cultured in recirculating aquaculture system (RAS) for 80 days, so that suggesting to adopt the technology hence overcome the challenges mentioned. Fish with initial body of 15.76g, were stocked at three stocking density 1,000, 1,500, and 2,000 fish/m3. Fish were fed 40% protein pellet twice a day at ad-libitum rate. Water quality parameter accumulation; highest NO2--N was founding in 1,000 fish/m3 stocking density 0.99 mg/l and lowest in 2,000 fish/m3 of stocking density 0.5818 ±0.17 mg/L. pH was maintained 7-8, DO oxygen was low in high stocking density, and the average temperature was 27 ºC during culture period. The increase in stocking density causes the increase in TAN, NO2--N in the filtration systems (1.37 ± 0.74 mg/L, 1.38 ± 0.23 mg/L, 2.31 ± 0.41 mg/L), (0.48 ± 0.17 mg/L, 0.58 ± 0.15 mg/L, 0.61 ± 0.25 mg/L) although statistically shows no significantly different . TSS and NO2--N retained in the water were high from the suitable ranges for healthy growing fish in all treatments. Fish growth performance (SGR, SR, WG, BW, and FCR), were not significantly different in all treatments. Biomass of fish was high in 2,000fish/m3 of stocking density 116.04 ± 16.66 kg/m3. Based on the treatment 2,000fish/m3 is the best result because of the higher weight and the same water quality with other densities. Water quality can be managed in the system by removal of waste water of volume of swirl separator (TSS control) and strong aeration in the biofilter tank to facilitate nitrification process. Further studies on mass balance should be conducted to design the best mechanical filtrations.