WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2019 61 (CONTINUED ON PAGE 62) recognized by feeling the roughness of the inner side of the pectoral fin. Mature females have a bulging abdomen, slightly swollen genital aperture and oozing ova when gentle pressure is applied to the abdomen (Fig. 1). Mature males are identified by no noticeable bulging of abdomen and milt oozing freely with gentle pressure on the abdomen. Broodstock Management The success of breeding by artificial means depends on a sufficient number of quality broodfish. Broodfish are selected by sex and held in separate ponds or tanks for one week prior to breeding. Identification of male and female brooders is based on the external features described previously. An average weight of 150-200 g is good for breeding. Rectangular ponds of 0.2-0.5 ha with 1.5 m average depth is preferred for broodfish raising (Fig. 2). Broodstock ponds and tanks should be covered with netting. Pengba broodfish should be fed daily with a 25-30 percent crude protein pelleted feed. In certain locations or for various reasons, it is not always possible to obtain and provide a high-protein pelleted feed. As an alternative, a mixture of mustard oil cake, fishmeal, rice bran, and wheat flour can be pulverized, mixed and fed in dough form. Broodfish condition should be examined regularly. Broodfish are harvested by lowering the water level during the breeding season. A day prior to induced breeding, selected broodfish from the earthen pond are held in separate enclosures or hapa nets (3.5 × 1.5 × 1 m) or spawning pools for acclimation and not fed. Constant water flow is maintained to ensure proper aeration. Handling of fish should be done very carefully to avoid possible injury and secondary infection. Induced Spawning Selected brooders should be administered with inducing hormone (e.g., Ovaprim) at 0.5 mL/kg female and 0.25 mL/kg male. Fish are injected intramuscularly on the caudal peduncle or behind the dorsal fin but above the lateral line using a 1-mL syringe (Fig. 3). To achieve successful induced spawning, it is advisable to put together one female with two males when breeding is done in hapas. In an eco-hatchery, the male to female ratio can be 1:1 provided males are of equal size and strength. After administering the hormone, broodfish are released into the breeding pool (Fig. 4), provided with water flow through a shower head to stimulate natural conditions, and not disturbed. Water inflow to the central outlet (egg delivery pipe) and single inlet must be adjusted in such a manner that it creates a current velocity of 3-5 cm/sec, maintaining the requisite water depth that simulates riverine flow. Within 5-6 hours after hormone injection, broodfish will show chasing behaviour that will continue for one hour. Chasing leads to courtship, locking and finally spawning. When the female releases the eggs, the male ejects milt and fertilization takes place externally. Egg Incubation and Hatching Spent brooders are removed and then eggs are collected from the egg collection chamber and transferred to the incubation pool for hatching (Fig. 5). The incubation pool (depth: 1-1.5 m) is circular, with an outer chamber that is 3-6 m in diameter and an inner chamber that is 1-1.5 m in diameter (Fig. 6). The circular wall that separates the outer and inner chamber is made of wire mesh. The inner chamber is wrapped with a nylon cloth that allows water from FIGURE 3. Administration of agent to induce spawning. FIGURE 4. Breeding operation in a spawning pool. FIGURE 2. Earthen ponds for rearing of pengba broodstock.
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