60 JUNE 2016 • WORLD AQUACULTURE • WWW.WAS.ORG cement platform on which plastic tubs are placed (Fig. 2). Water is provided from an overhead tank through a common pipe to each tub with individual control taps. Each tub has a provision for an outlet at a water level of about 4-5 cm. A row of small tubs of 12-cm diameter with 6-cm height is placed under separate taps. Each plastic tub can accommodate approximately 1,000 eggs. For large-scale incubation, an improvised Portable FRP Magur hatcheryTM was developed by ICAR-CIFA (Fig. 3). The system consists of a circular tank of 2-m diameter with five to six inlets at the junction of the tank wall and bottom surface. The tip of the inlets are designed as a duck bill to provide turbulent water flow and are fitted at an angle of 45°. This system can accommodate about 30,000 fertilized eggs in a single cycle. Fertilized eggs are spread uniformly on the tank bottom and a feeble water current is provided to maintain an optimum oxygen level. Some progressive farmers have imitated models of the two hatchery designs described previously. These hatcheries were built to reduce construction or purchase cost and are now in regular use for seed production (Figs. 4a, b). Hatching occurs within 24-26 h at 27-30 C in this tropical climate. After hatching, newly hatched larvae in the tub are frequently washed to make them free of eggshells and unhatched eggs. Hatchlings are transferred to circular/rectangular fiberglass or plastic containers for further rearing. Larvae to Fry Production Because larvae are small and delicate (4-5 mm length and 2-3 mg wet weight), they require captive rearing in indoor systems. Many times, hatchery producers release larvae directly into nursery ponds or after nursing a few days in indoor systems. However, the net recovery declines drastically in this situation. Research institutions have provided training and demonstrated systematic rearing in indoor conditions. In occasional cases, high-density rearing (up captive conditions (Fig. 1b). Researchers and farmers usually use commercially available synthetic hormones (Ovaprim/Ovatide/ WOVA-FH) at 1.0-1.5 mL/kg body weight as an agent to induce ovulation (Sahoo et al. 2005a, b, Srivastava et al. 2012, Sinha et al. 2014). Apart from this, other inducing agents, such as conventional carp pituitary extract at 30-40 mg/kg body weight and human chorionic gonadotropin at 3000-4000 IU/kg body weight have been used successfully for experimental purposes (Goswami and Sarma 1997, Sahoo et al. 2007 and 2008, Dhara and Saha 2013). Male broodfish do not ooze sperm on their own, unlike carp varieties and do not receive injections, as do the female broodfish. Testes are removed and macerated in normal saline (0.9 percent sodium chloride) to prepare a sperm suspension that is required for fertilization of ovulated eggs. Often some farmers inject males with half a dose of the hormone (0.5 ml/kg body weight) to obtain better milt quality. However, males do not require hormonal induction of spawning. Hatchery operators undertake stripping of females after a latency period of 16-17 h to get the best-quality eggs. Fecundity is about 5,000-6,000 eggs per 150-g female. Eggs are fertilized with a sperm suspension, followed by a thorough washing of fertilized eggs before transferring to the flow-through hatchery for incubation. Types of Hatcheries Different types of egg incubation devices are seen for incubating the fertilized eggs of magur. A flow-through hatchery consists of a FIGURE 2. Flow-through magur hatchery developed by the ICAR-CIFA for egg incubation. FIGURE 3. Flow-through magur hatchery developed by the ICAR-CIFA for egg incubation. FIGURE 4a. Flow-through hatchery developed by a farmer. FIGURE 4b. Magur hatchery imitated by the farmer following the Portable FRP magur hatcheryTM design.
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