EFFICACY OF VARIOUS BIOFILTER MEDIA IN A CLOSED RECIRCULATING SYSTEM FOR LARVICULTURE OF MACROBRACHIUM ROSENBERGII

Abstract

Efficacy of 4 different biofilter media viz. plastic bio-balls, charcoal, zeolite stones and molluscan shells was evaluated in a closed recirculating system for larviculture of Macrobrachium rosenbergii. The larvae of M. rosenbergii were reared in 3 cycles using natural and synthetic seawaters. The larvae were stocked @ 100 per liter and reared till 9096 larvae metamorphosed into post-larvae (PL). The results indicate that all biofilters are capable of maintaining water quality parameters within the optimum range. Concentration of ammonia (NH₄+-N), nitrite (NO₂ -N), nitrate (NO₃ -N and phosphate (PO₄,-P) were significantly (P <0.05) lower in recirculatory system with synthetic seawater as compared to natural seawater. The larvae of M. rosenbergii tolerated a wide range of concentrations of ammonia (0.12 to 0.63 pm) and nitrite (0.04 to 0.35 ppm) without affecting production of post-larvae. The performance of molluscan shells was significantly (P<0.05) better than other biofilters, irrespective of rearing media. A biofilter volume equivalent to 696 of the volume of larval rearing tank and rate of filtration of 252 L h-' were found to be ideal. An average production of 44.93 and 40.92 PL per L was obtained in synthetic and natural seawaters, respectively.