WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2014 53 (CONTINUED ON PAGE 54) The Yellow Catfish Yellow catfish is endemic to Western Ghats of Kerala, India and shows very limited geographical distribution (Fig. 2) in India (Bhat 2001). The population of yellow catfish in nature is in gradual decline from overfishing throughout the river belt, destruction of spawning grounds and barriers across rivers. For this reason, this species is listed by the IUCN as vulnerable (Kurup et al. 2004, Ali et al. 2007). Its adaptability in different environments, its acceptance of a wide range of food and good growth and survival in confinement makes it a prospective species for diversification in aquaculture. The fish is moderately elongated with a compressed body. It has a sub-terminal mouth with four pairs of barbels. The eyes are large and placed slightly below, which helps the fish see the bottom during feeding. Dorsal and pectoral fins possess strong, serrated spines that can cause painful injury if handled carelessly. It performs well at a pH of 6.5-7.5 and water temperatures of 2730º C. Males and females grow isometrically. Yellow catfish feed on aquatic vegetation, crustaceans, insects, fish larvae and detritus in natural water bodies (SreeRaj et al. 2006). Preferences for food items are size specific. Gut content analysis indicates that the proportion of crustaceans in the stomach decreases as the fish grows. Fullness of the stomach is easily observed during the post-monsoon period. Feeding intensity is affected during the pre-breeding season and the monsoon period. It has the capability of widening food choices as a function of food availability. Yellow catfish will mature in confined water, with males maturing earlier than females. Males of 10-15 g start oozing milt in the first year of life under captive conditions and females mature in the second year. Absolute fecundity increases as length and weight increases (Kurian and Inasu 2003). The fish breeds in natural waters during monsoon periods. Hatchery Propagation Broodstock management. Yellow catfish adapts well to fresh water and cement tanks and earthen ponds can be used to raise broodfish. Broodfish of 80-100 g are the most suitable size for an induced breeding program. Feeding broodfish with a balanced diet and providing clean water are some of the management tools for obtaining good broodfish performance. Water quality parameters for raising brooders should be pH 6.5-7.5, dissolved oxygen of 5-6 mg/L and alkalinity of 120-125 mg/L as CaCO3. Broodfish accept pelleted feeds in captive conditions and the feed protein content should be 30-32 percent, fed at 2 percent of body weight daily. Brooders are stocked at low density (1-2/m2) in ponds to minimize competition during feeding. Selection of broodfish. Morphological identification of males and females is only possible during the spawning season (July-August). The genital papillae in both sexes are identical so it is essential to press slightly above the genital papilla to see free oozing milt to identify males. The abdomen of the female bulges and yellowish uniform eggs can be expressed by slight pressure near the vent. Females at first maturity do not respond well to hormone injections on many occasions. Therefore, it is essential to select females of at least 80 to 100 g. Induced breeding. Ovaprim is best for induced breeding in yellow catfish. Females need a single injection of Ovaprim at 1-1.5 mL/kg body weight (Sahoo et al. 2014) and after 12-13 h a free flow of eggs usually is observed in response to gentle pressure on the abdomen. Ovulated eggs are yellowish and the fecundity is about 15,000-18,000 per 100 g female. Milt expressed from one male is sufficient to fertilize eggs of a female of the same size. Eggs and milt should be mixed thoroughly to fertilize the eggs, which are then incubated in a flow-through hatchery system. Hatching is observed 21-22 h after egg fertilization. Newly hatched larvae are 4-5 mm in length and 1-2 mg in weight (Sahoo et al. 2011). Egg fertilization is typically 60-80 percent and hatching is about 40-60 percent. Reduced fertilization and hatching rates are generally a result of improper selection of broodfish for induced breeding, which produces immature eggs. Seed Rearing Larval rearing. Larvae need to be reared in an indoor system to obtain greater survival. The indoor system is comprised of fiberglass or smooth bottom ferrocement tanks with aeration. Hatchlings should be distributed into rearing tanks. Healthy larvae will migrate to the periphery of tanks by a slow tail-lashing movement. Deformed larvae and unhatched eggs that accumulate in the tank center must be removed daily. The yolk-sac provides nutrition to the larvae until three days after hatch. Because mixed zooplankton remains alive longer in freshwater, it is the best food for larvae from the fourth day after hatching. Maintaining 12-15 cm water depth, continuous aeration and the cleaning of tanks twice per day are some of the important husbandry practices (Sahoo et al. 2014). Larvae also accept compound feed from 10-11 days after hatching. Feeding live feed and compound feed (35 percent protein) to larvae enhances growth and survival rate. Improper cleaning leads to stress and secondary infection in the larvae from the accumulation of uneaten feed and dead plankton present on the tank bottom, resulting in larval mortality. Highdensity rearing (3000-4000 larvae/m2) also results in low survival and growth. Hence, a low to medium larval density (500-1000/m2) results in greater growth (50-60 mg) and survival (>60 percent) FIGURE 2. Geographic distribution of yellow catfish in India.
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