WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2017 57 maintained at about 60 cm in each hapa. Fish fry were fed three times per day at 5 percent body weight throughout the experimental period. Results and Discussion Despite regular checks for maturity of females, few mature females were found, while more females were collected that were overmature. Of 35 female fish reared, 15 were determined to be overmature during regular observations (Table 1); over-mature fish were found from November through March. One female was ready to spawn without injecting hormone (natural breeding) on 9 March when water temperature was between 23.3 and 25.2 C. Similarly, breeding of a hormoneinduced female occurred on 26 March at temperature between 25.3 and 28.7 C (Table 2). The total number of eggs obtained from the natural breeding female was 2,585, while 4,738 eggs were obtained from the hormone-induced female. Relative fecundity was 2,119 and 3,746 per kg for natural and hormoneinduced breeding, respectively. For females with no hormone induction, 1 g of ovulated eggs contained 94 eggs, while in hormoneinduced females, 1 g of ovulated eggs had 103 eggs. Testing for spawning condition at the correct time is critical for sahar breeding, and thus, examination of female fish for maturity must be done frequently. As reported by Bista et al. (2010), pond-reared sahar spawn intermittently, and determining optimum timing for egg stripping by frequent checking of brood fish may result in a spawning success rate of more than 50 percent. Although we conducted frequent examination of broodfish in this study, 15 females were over-mature, while successful breeding was attained only in two females. Overripe females were recorded when temperature ranged between 15.5 and 28.7 C, from the last week of November to the last week of February. Bista et al. (2010) reported that spawning occurred when temperature ranged between 26-27.4 C on one occasion and 20-21 C on a second occasion in Pokhara, and there were more spawners in February and March compared to September and October. Pandey et al. (1998) reported spawning was induced successfully by hormonal injection when water temperature in ponds was 18-24 C. However, the dose administered in that study was lower (0.2 mL/kg body weight) than we used. Bista et al. (2010) also reported that diameter and weight of fertilized eggs were 2.87±0.13 to 2.98±0.08 mm and 13.9±0.9 to 15.4±1.3 mg, respectively. They also reported an incubation period of 45-125 hours at water temperatures from 19-28 C. The length and weight of the newly hatched larvae in our study were similar to those obtained by Bista et al. (2010). The egg fertilization rate for natural and hormone-induced breeding was over 98 percent, and the incubation period was 96-104 hours for natural and 80-88 hours for hormone-induced breeding. Hatching rate was over 95 percent in natural and induced breeding. Hatchling survival was 81 percent for natural breeding and 90 percent for hormone-induced breeding (Table 2). Newly hatched larvae from natural and hormone-induced breeding were similar size at hatching (Table 3). Yolk sac absorption was slightly longer for natural breeding (6 days at 19.4-26.2 C) compared to induced larvae (5 days at 24.8-27.2 C). Length and weight at yolk sac absorption were also similar for both larval types. During broodfish rearing, temperature ranged from 14.3 to 38.2 C (Fig. 1), DO from 1.4-13.5 mg/L, and average pH from 6.5 to 8.2. Natural spawning occurred when water temperature was between 23.3 and 25.2 C, while induced spawning occurred when water temperature (CONTINUED ON PAGE 58) FIGURE 1. Average water temperature of the sahar brood pond at morning and evening each month during brood rearing. FIGURE 2. Growth performance of sahar fry fed with commercial or local feed. One-month old sahar fry. Net boxes for fry nursing and rearing.
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