IMPACT OF BIOFLOC ON THE NURSERY REARING OF PEARL SPOT Etroplus suratensis UNDER FLOW THROUGH SYSTEM
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Date
2018
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Fisheries College and Research Institute, Thoothukudi, Tamil Nadu Dr. J. Jayalalithaa Fisheries University
Abstract
The present study was conducted to evaluate the biofloc technology on water quality and growth performance of pearl spot (Etroplus suratensis) young ones in outdoor nursery tanks. The experiment consisted of treatments (T1- Jaggery, T2- Cassava flour and T3- Corn flour treated) and control (sugar treated) group. Floc development was done with addition of different carbon sources as described above with a carbon/nitrogen (C/N) ratio of 15:1 in a reservoir tank which is connected to rearing tanks by flow through system. The stocking density was 25 numbers per tank. The mean length and weight of Pearl spot E. suratensis were ranging from 2.62 ± 0.005 cm to 2.71 ± 0.005 cm in length and 1.05 ± 0.002 g to 1.08 ± 0.002 g in weight. Ammonia-N level in the biofloc treated nursery rearing tanks was lower (0.04 to 0.12 μg-at-N/l) than biofloc holding reservoir tanks (0.51 to 2.65 μg-at-N/l). In control experiment where sugar was used as a carbon source, higher value of ammonia-N content than the other treatment tanks was recorded. The maximum mean floc volume was observed in Jaggery treated (T1) experimental reservoir tank (12.37 ± 0.024 ml /l) whereas the minimum mean floc volume was observed in control (C) biofloc reservoir tank (11.7 ± 0.023 ml /l). Total suspended solids concentration continuously increased in biofloc reservoir tanks and the readings ranged from 18.48 ± 0.73 g/l to 21.37 ± 0.32 g/l in which the highest value was observed in control tank. Jaggery and sugar are simple carbohydrates, easily assimilated by bacteria, while cassava flour and corn flour is constituted of complex carbohydrates, which need to be broken down to get assimilated by heterotrophic bacteria. The regression coefficient in the length weight relationships are highly significant (P<0.01) and the ‘b’ value (1.9085) recorded in T1 (Jaggery) was greater than that recorded in the control which confirms better growth performance. The mean length gain of fishes in T1 (Jaggery) treatment tank was observed as 4.57 ± 0.02c cm and the mean body weight gain was 3.61 ± 0.03c g which was higher than the other treatments and control. The growth increment in Treatment-1 when compared with control was 23.8%. From the present study it is evident that experimental biofloc treatment with Jaggery can improve the quality of culture water and results in better growth of pearl spot compared to Sugar, Corn flour and Cassava flour treatments as a carbon source.
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