Effects of Feed Additive Probiotics on Growth Performance of Blackhead Seabream(Acanthopagrus Schlegelii) and Water Quality in Recirculating Aquaculture System(RAS)

Abstract

Recirculating aquaculture systems (RAS) for fish culture has been used for decades. The RAS system has advantages of using small land area and minimal water volume for intensive production. Although RAS has proven to be very efficient, it still has some challenges. One of such challenges is poor water quality (high levels of ammonia nitrate and nitrite nitrate) which mainly emanates from accumulated fish waste and uneaten feed. Probiotics have been adopted by many fish farmers as the best alternative to control microbial infections compared to antibiotics, as it improves water quality, boosts fish immune system and helps fish growth. Although many researches have been conducted on the effectiveness of probiotics in ponds and laboratory, little research has been done on its effectives in improving water quality and fish growth in the RAS. To investigate the effectiveness of probiotics in promoting fish growth and water quality, a 60-days experiment was carried out in a RAS on blackhead seabream, Acanthopagrus schlegelii using commercial probiotics. The experiment was conducted in four identical RASs and each system consisted of three tanks (70 L each) with a water treatment system. Fifty fingerlings (34 ±0.20 g, 5.95±0.25 cm) were stocked per tank in all the 12 tanks. Probiotics was applied to fish feed in three different concentrations (2.5 g/kg feed T-1, 5 g/kg feed T-2, 10 g/kg feed T-3) and were fed twice daily. Water temperature was controlled using an electric heater with a thermostat and was maintained at 24.5±0.5oC. Salinity and pH were maintained at 29.5±0.5 ppt and 7.5±1.0 respectively. Specific growth rate (SGR), food conversion ratio (FC), protein efficiency ratio (PER), survival rate (SR) were measured to assess the growth performance and DO, pH, ammonia nitrogen (TAN), nitrite-nitrogen (NO-2-N) and nitrate-nitrogen (NO-3-N), chemical oxygen demand (COD) biological oxygen demand (BOD5), water color, turbidity were also measured to assess the water quality status during the experimental period. The results showed significant improvement in water quality in probiotics treated tanks as there were reductions in TAN and NO-2-N, COD, BOD5, turbidity levels (P<0.05) than in control. The DO and pH, did not show significant differences (P>0.05) among all the groups although lower levels of pH and DO were recorded in T3. However, there was significant difference in DO (P<0.05) between T2 and T3 and between control and T2. The growth parameters of the fish did not show any significant difference (P>0.05) among all groups as SGR, FCR, PER, SR, average body weight and body length were all statistically not significant (P>0.05). In this study, probiotics appeared to have effect on improving water quality in the RAS but did not show any clear improvement on fish growth in such experimental period.