World Aquaculture - December 2014

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• WORLD AQUACULTURE • DECEMBER 2014 53
( C O N T I N U E D O N P A G E 5 4 )
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 27-
30º 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. High-
density 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.