P. Jayasankar

Recycling of Sewage in Aquaculture: Decadal Technical Advancement

Freshwater is indispensable for sustenance of life on earth, but is rapidly becoming a scarce resource. A centre on wastewater aquaculture was established during the 1970s in Rahara, Kolkata, which initiated research on recycling of sewage water for production of fish through nutrient recovery. Huge volume of sewage water has been treated through different convenient modes and monitored for probable hazards of sewage water before its utilization in aquaculture. Both chemical and biological contaminants were reduced by 80% by different treatment methods. Using specialized farming management protocols through a series of culture trials, it was possible to achieve the fish yield to the tune of around 5.0 t/ha/year. Different aspects of farming such as species selection, stocking density, species ratio, choice of species groups, stocking and harvesting relation and postharvest techniques were considered. Following the WHO guidelines of risk involved in sewage-fed aquaculture, different parameters such as microbial loads, heavy metals and herbicides after sewage intake were analysed and found below safe limits. Using bioassay trials, the impact of sewage with different sewage dilutions has been optimized. Health and hygiene of handlers were critically assessed, but no adverse impacts have been observed. Sewage-fed aquaculture has great potential to develop into an effective alternate system of fish production in the backdrop of freshwater scarcity and increased farm income, though consistent monitoring is entailed from the health and hygiene perspectives.

Efficacy of exogenous hormone (GnRHa) for induced breeding of climbing perch Anabas testudineus (Bloch, 1792) and influence of operational sex ratio on spawning success

The climbing perch, Anabas testudineus, is an air-breathing fish having great consumer preference as a food fish and is considered a prime candidate species for aquaculture. Spawning success is an important issue while using hormones for captive induced breeding. In the first experiment, a trial was conducted to assess the efficacy of a synthetic Gonadotropin Releasing Hormone analog (sGnRHa) on the spawning success of climbing perch. Female fish were administered six different doses each with a single intramuscular injection of sGnRHa hormone at 0.002 (TOD1), 0.005 (TOD2), 0.01 (TOD3), 0.015 (TOD4), 0.02 (TOD5), 0.03 (TOD6) μg/g body weight. Similarly, males were administered half of the hormone dose of females in all the respective treatment groups. The greatest (P<0.05) relative fecundity (715.13±15.0 eggs/g female body weight) and fertilization percentage rates (93.1±8.0%) occurred when female fish were treated at the 0.015μg/g body weight dose. There was a reduction in relative fecundity and hatching rate in female fish injected with the largest dose (1.5μL/g body weight) of sGnRHa. A second experiment was conducted to assess the effect of a different male-female ratio on optimum spawning success in climbing perch. For this study a different female to male ratio (1:1, 1:2, 1:3 and 1:4) and male to female ratio (1:1, 1:2 and 1:3) were used. There were a greater (P<0.05) relative fecundity (886.62±17.9 eggs/g female body weight), fertilization (98±6.7%) and hatching (99±5.4%) rates with the female to male ratio of 1:2. This indicated that the hormone dose of 0.015μg/g body weight and a female-male ratio of 1:2 are optimal for enhanced spawning success in the climbing perch.

Tubifex production using agro-industrial wastes and raw cattle dung

ABSTRACT Tubifex (Tubifex tubifex) was cultured in captivity using three different wastes: rice mill sludge (RMS), dairy sludge (DS), and raw cattle dung (RCD). Three experiments were conducted: 10, 20, and 30 days. A total of 100 g of tubifex at 62.5 g m−2 was inoculated in 1.6 m2 fiberglass-reinforced plastic tanks. Comparing all production parameters, RMS > DS > RCD. Growth rate (g m−2 d−1) did not differ among durations. RMS- and DS-fed tubifex contained higher protein and fat than RCD-fed tubifex. Efficiency on production of g tubifex per kg of waste material was highest at 10 days, declining with time for all waste materials. This experiment suggests that RMS and DS are effective wastes for tubifex culture, with total production increasing with no reduction in growth rate through 30 days, but with efficiency declining after 10 days.