Author(s): Sudhir Krishan Garg and Shivani Bhatnagar

Abstract: To investigate the optimum density of additional substrate required for obtaining higher growth of Oreochromis niloticus in brackish water ponds (salnity: 14~16 ppt, temperature: 27.4 ~ 32.3 ^oC), three different densities of bamboo poles (at 375, 560 and 750 per pond of 375-² meters) each in replicate of two were maintained. Fish fry (mean body weight 0.94-0.96g) were stocked in ponds at 10000 fish ha-¹. During the experimental period, all the water quality parameters remained within the optimum range. After a grow-out period of 100 days, a significant (P<0.05) increase in fish growth indicating parameters i.e., mean weight (g), length (cm), growth day-1 and specific growth rate (SGR) and higher values of productivity indicating parameters were observed in ponds provided with substrate density i.e.,560 bamboo poles. Higher values in dry matter contents and periphyton biomass were observed at a depth of 50 cm which coincided with the photosynthetic compensation depth. Periphytic dry matter, periphyton number, total pigment concentration, algal constitute of periphytic biomass and periphyton productivity were also significantly (P<0.05) higher in ponds provided with substrate density at 560 bamboo poles. In other words provision of substrate at 54 per cent of the total submerged surface area appeared to be sufficient for periphyton production and obtaining optimum growth of Nile tilapia. Findings suggest that with the provision of optimum density of the substrate, periphyton supported production technology can offer considerable potential for enhancing aquaculture production without any deleterious impact on pond ecosystem.

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