WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2016 61 to 10,000 larvae/m2) was encountered in some hatcheries, even after recommending the optimum stocking of 1,000-1,500 larvae/ m2 during indoor rearing (Sahoo et al. 2004, Sinha et al. 2014). This situation sometimes happens because of space limitations, as explained by hatchery operators, and larvae are thinned in subsequent days during rearing. The aquatic environment and water quality plays a major role in successful nursing of larvae. Rearing tanks must be provided with continuous aeration, inasmuch as aerial respiration commences 1011 days after hatching. Degradation of water quality is common as a result of the accumulation of metabolites and unconsumed feed in the rearing systems. Free ammonia is toxic at low concentrations, affecting gills and accessory respiratory organs and hydrogen sulphide causes stress. During high-density fry rearing, increased carbon dioxide concentration in the environment also may be a stressor. Hence, it is beneficial to clean accumulated metabolites from rearing tanks and replenish 70-80 percent of the water volume daily (Table 1). Feed management is also one of the most vital parts of successful larval rearing. Tiny yolk sac larvae are able to accept feed on the fourth day because the yolk sac is absorbed during the third day. By this time, hatchlings became longer, with prominent barbels, FIGURE 5. Starter-M, a larval feed developed by ICAR-CIFA for the rearing of magur. FIGURE 6. Healthy magur fry (15-20 days) reared in an indoor system. FIGURE 7. Occurrence of filamentous algae in nursery rearing tanks. FIGURE 8. Fingerlings (2-3 months old), an ideal size for grow-out. (CONTINUED ON PAGE 62) TABLE 1. Optimum water quality parameters for rearing larvae and fry of Clarias batrachus. Water quality parameter Optimum range Water temperature (C) 27-30 Dissolved oxygen (ppm) > 3 Carbon dioxide (ppm) < 8 pH 7.3 - 8.5 Alkalinity (ppm) 90 -160 Hardness (ppm) 80-150 Ammonia (ppm) < 0.1 Nitrite (ppm) < 0.05
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