62 JUNE 2019 • WORLD AQUACULTURE • WWW.WAS.ORG the outer chamber to the inner chamber. Fertilized eggs are spherical, translucent and demersal, measuring 2.5-2.8 mm in diameter. Eggs are incubated in the incubation pool at 750-1,000 eggs/L. Hatching takes place 18-20 h after fertilization and hatchlings are visible after 24-26 hours at 26-30 C. Finally, the spawn delivery pipe delivers the spawn to the spawn collection chamber. Newly-hatched larvae measure about 4.5 mm in length and 1.4 mg in weight. Larvae depended on yolk sac reserves for up to 72 h. On the fourth day, hatchlings measure 6.5-7.0 mm in length and are released into a nursery tank for further rearing. Larval Rearing and Fry Production The nursery phase involves rearing 4-d old hatchlings in earthen nursery ponds for 20-25 days until they grow to fry stage (20-25 mm). Generally, smaller seasonal ponds of 0.02-0.1 ha size with average water depth of 1-1.5 m are preferred for rearing. Nursery pond preparation prior to stocking of larvae includes removal of aquatic weeds and predatory fish, followed by liming and fertilization with organic manure and inorganic fertilizer. Aquatic insects are eradicated by the application of a soap-oil emulsion or removed by repeated netting before stocking. The recommended stocking density is 300-500/m2. Hatchlings can be fed with a supplementary feed made of a 1:1 mixture of rice bran and groundnut oilcake in powdered form. Powdered feed is broadcast over the water surface for easy availability to the seed. Survival ranges from 30 to 50 percent. Feeding larvae with live organisms, particularly zooplankton, have always proved best. There is a chance of mortality and poor growth of larvae due to a poor environment during pond nursery rearing (Table 1). For this purpose, concrete tanks (50-100 m2) provided with a soil layer of 15 cm are effective for raising (Fig. 7). A stocking density of 1000-2000/m2 is considered for good growth and survival in outdoor concrete tanks. Larvae grow to 20-25 mm fry during 20-25 days of rearing. Thinning of the population is required if the seed are to be retained beyond this period to avoid mortality. After that, resulting fry should be transferred to rearing ponds for fingerling production. Fingerling Production The rearing phase refers to the rearing of the fry in earthen rearing ponds (0.05-0.2 ha) with 1.2-1.5 m water depth for 2-3 months till they grow to fingerlings (80-100 mm) (Fig. 8). Standard pre-stocking management practices should be taken prior to the stocking of fry. The recommended stocking density is 30/m2, but higher stocking density can also be used in well-managed ponds with water circulation and aeration. Normally survival of 60-70 percent is achieved in this rearing system. Generally, pengba fry are reared along with Indian major carps in ponds or tanks. Nutritional requirements can be met through natural food along with a supplementary feed made of a 1:1 mixture of rice bran and groundnut oilcake in powdered form. Moreover, the COF-CAU developed the incorporation of Wolffia globbosa, an aquatic fern, as a sole food in fresh and dried form during fry rearing to be ideal owing to better pengba survival and growth rate. Grow-out Culture Earthen ponds or cement tanks are suitable for grow-out culture of pengba. A stocking density of 1/m2 is recommended for culture of this species in monoculture. Fish are fed with pelleted feed (2025 percent crude protein) at 3-5 percent of their body weight twice daily in two equal parts. Fish reach a market size of about 400-500 g within one year and production of 1.5-2 t/ha can be achieved. The rearing of pengba in grow-out polyculture with major and other carps has gained importance in India. FIGURE 7. Outdoor cement tanks for nursery rearing of pengba. FIGURE 6. Incubation of fertilized eggs in a spawning pool. FIGURE 5. Egg collection after a successful spawning.
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