Introduction
The freshwater catfish, Clarias ssp. are widely distributed in Southeast, South Asia and Africa. They exist in a variety of habitats from brackishwater in estuaries to fully freshwater rivers and lakes. In the mid- 1990's, and introduced species, Clarias gariepinus, have become a very popular aquaculture species in the country because they can be spawned artificially, grow very fast, can tolerate farming conditions and are easy to culture.
In the Philippines, there are now three species of the genus Clarias, namely, the Native Hito (Clarias macrocephalus, the Thai catfish (Clarias batrachus) and the African Hito, (Clarias gariepinus). Among the three species, only C. macrocephalus is indigenous in the Philippines while the other two are introduced species. C. gariepinus originated from Africa while C. batrachus came from Thailand. The introduction of these species into the country was believed to have contributed to the diminishing population of the native catfish. To date, the native catfish can scarcely be found only in some remote areas of the Philippines namely Mindoro and Palawan where the two other species have not been introduced before.
Among the three species, the Native Hito is still the more preferred species due to its tender and more delicate taste as compared to the Thai Hito which has a rubbery flesh and the African Hito which has tender but dry fibrous flesh. However, with regards to the growth rates, the Native Hito is the slowest grower among the three. The African catfish is the fastest grower followed by the Thai catfish. The Native Hito is by far the best tasting among the three according to a lot of people.
Biology of the Native Catfish
Morphological Identification
Catfish have scaless slimy skin, which is darkly pigmented in both the dorsal and lateral part of the body. The fish is light in color when kept in turbid water. It turns dark in clear water.
C. macrocephalus is closely related to C. batrachus. The species can be distinguished by the shape of the occipetal process, which is more pointed in C. batrachus and evenly curved in C. macrocephalus. C. gariepinus on the other hand has three pointed occipetal process. (Fig. 1).
The body is elongated with a broadly depressed head, four pairs of barbels and small eyes. There is a nearly smooth pectoral spine. The dorsal fin almost reaches the caudal fin. The pectoral spine is robust, serrated only on its outer face and the number of serration increases with age.. The developed strong spines are used for locomotion and protection. The sharp spines are not poisonous.
Catfishes have both gills and aborescent organs which enables them to breathe atmospheric oxygen and dissolved oxygen in the water. This ability also allows the catfish to thrive even poor water quality conditions. It can survive out of the water for some hours depending on the humidity in the environment.
In male and female catfish, the urogenital opening is located at a papilla just above the anus. Males have elongated papilla while the females have mole like structure.
The native catfish matures in 8-12 months at a weighted average of 150-250 g.. Spawning usually does not occur unless the final stimulus such as fluctuations in temperature, rise and fall of water level or increased dissolved oxygen are met. The fish can however be spawned by using hormonal treatments. The broodfish raised in ponds normally remain mature during several months of the year. A broodfish can be artificially spawned several times during these months.
Spawning in the wild occurs during the rainy season, from May to October. The C. macrocephalus female makes a small round nest with a grassy bottom. The eggs are deposited in the nest and attached to the roots of aquatic plants. The male takes care of these eggs until they hatch. A female weighing 150-200 g can produce between 5,000-10,000 eggs.
The Native Hito is nocturnal and can thrive at high stocking densities because of their air breathing capability. They are usually found in canals, swamps and paddy fields. In the wild, the fry feeds on prtozoans and small crustaceans and when they grow bigger, they feed on worms, insects and are also scavengers of dead vertebrates.
Grow-out Culture
The Native Hito can be cultured in either earthen ponds, or concrete ponds or cages.
The ideal size of the earthen pond is 400-1,600 m2 with water depth of 100-150 cm. Ponds are prepared by draining out the water and all fish are removed. The pond bottom is dried and lime is added at a rate of 300-500 kg per hectare to improve the pH condition of the ponds. At the same time, 0.1-0.2 kg/m2 of chicken manure is applied. The pond should be filled to a depth of 30-40 cm water through a fine mesh net to prevent entry of predators.
Stocking density
The stocking density of 2-3 cm fingerlings is about 50-60/m2
It will take about 4-5 months for the fingerlings to grow to 150 g. The average recovery rate is 75%.
Practically on the first stocking day, 40% formalin is splashed all over the pond to make 40 ppm concentration at a water level of 40 cm. Every week, the water level is increased by about 10 cm until the water level is 1.0-1.5 m deep.
Water exchange at the rate of 10-30% every 5=7 days usually starting after the second month. Formalin is also splashed in the pond after the second month at the rate of 40ppm to prevent disease. As the water turn dark then green, water will have to be changed as this indicates water pollution. Lime should also be broadcasted along the periphery of the dike at the rate of 30-50 kg/500 m2.
Feeding
It is not necessary to feed the fingerlings on the first day of stocking as they have enough food in the earthen pond.
In the first week, Moina should be fed at the rate of 1-2 g/m2 . Powdered feed or small pellet feeds should be molded into paste (finger size lumps) by adding water and spreading evenly around the . The quality of feeds will shorten or lengthen the culture period. The major ingredients of the feed includes” trashfish, rice bran and broken rice. Formulated commercial feed pellets and chicken entrails are usually used to lower down the feed cost.
During the first month, they are fed 2 times a day and after that reduced to once a day. They ere fed with formulated combined with boiled broken rice or mixed feed of 55% minced trash fish, 15% fish meal, 25% rice bran and 1% vitamins and mineral premix. Feeding rate starts from 12% of the fish weight in the first week and gradually decreases to 3% in the 2nd week. Two crops of the Native Hito are raised per year at a harvest size of 150-250g. Production is 2-5 kg./m2 depending on the management.
Concrete Tank
Intensive culture of C. macrocephalus can be done in concrete tanks of 5 square meter. In fact, they can be cultured in abandoned pigpens. Water in new tanks should be changed many times to neutralize the cement prior to use. Fingerlings of about 2-3 cm in length are purchased at the price of about P 1.50 each and stocked in the tank at 30-50 pcs/m2.
Feeding in tanks are done with commercially available formulated feed. During the first few months, feed containing 30-35% protein are given. Then reduced to 30% protein for the next 1.5 months. About 1.5 months after harvesting, 25% protein is given instead. The culture period is 4-6 months at which time, they should average at 150 g. Total harvest should be around 66 kg/m2 tank.
Cage Culture
Net cages maybe stocked with the Native Hito at 100/m2. Cage culture has the following advantages:
1. When fish are crowded into small spaces, they burn fewer calories, thus food conversion is more efficient.
2. Easy to harvest,
3. Sustained levels of oxygen because water goes in and out of the cages.
4. Metabolites pass off the net enclosures.
In choosing a site for the cage culture of the Native Hito, factors such as protection, water current, depth, dissolved oxygen, and water pollution must be within suitable range. For instance, water current at 20-30 cm/sec. is optimum for water quality management in terms of water exchange to maintain dissolved oxygen and excretory product removal as well as minimizing stress on the fish.
Commercial Hito feeds maybe fed to growing Native Hito. Floating feeds may be beneficial especially in areas where the cage does not touch the bottom of the lake or river.
Feeds should be given gradually at 3-5% of the body weight at 2-3X per day adjusted weekly.
Harvesting and Transport
The fish at marketable size are seined continuously depending on the demand and wholesalers. During the last seining, the pond is drained and the fish are caught by scoop net. Hito has to be transported and sold live. Nobody prefers to buy dead Hito. They are transported in trucks in plastic drums at the rate of 70kg/drum filled with water. Transportation time can be as long as 10 hours.
The use of formulated feed is not economical for the native Hito culture in earthen ponds because the investment in feed cost is higher. The use of mixed feed (formulated: fresh feed) is recommended because the feed investment is lower. In tanks, formulated feed is recommended because production is more efficient and therefore, production cost is lower.
