EFFECT OF MICROBIAL BIOFILM IN THE NURSERY PHASE OF MRIGAL, CIRRHINUS MRIGALA

Abstract

The experiment was conducted for 35 days in nine cement tubs (1 x 1 x 1 m) having 15-cm sandy-loam soil base with three treatments in triplicate, viz., cow dung alone at the rate of 1 kg/tub (T1), cow dung at 1 kg/tub and feed at 10o/o body wt/d in two meals (T2), and cow dung at 1 kg and paddy straw at 200 g/tub (T3). Both manure and substrate were added on dry weight basis. AU the tubs were stocked with 10 fry each ofmrigal (100,000/ha) of average weight of0.09 g, seven days after the addition of manure and substrate. The total plate count of bacteria in water did not vary much between the treatments and the mean
values were 5.13, 5.49 and 5.85 (CFU x 1 O.j/ml) in T2• T2 and T3 respectively. The number of phytoplankters and zooplankters in water differed significantly between the treatments. The average number of attached algae (no./cm2 ) and fish food organisms (no./cm3
) recorded on the substrate were 145.28 and 70.67, respectively. The mean final weight of mrigal differed significantly (P < 0.05) between the treatments with T3 registering the highest value of 6.93 g followed
by T2 (5.01 g) and T1 (3.37 g). The specific growth rate and growth increment of fish also followed the same trend as that of weight recorded in the different treatments. Survival was higher in T2 (83.33°/o), followed byT3 (80.00o/o) and T1 (76.67%). The study demonstrates that by the introduction of biodegradable substrates like paddy straw into the culture systems, significantly higher growth and survival can be obtained in the nursery rearing ofn1rigal. 
Keywords : Microbial biofilm, nursery, Cirrhinus mrigala