River Catfish or Pagasius (Pangasius hypopthalmus) is a riverine catfish belonging to the members of the family Pangasidae. It is mainly found in countries within the Mekong Delta bordered by the Tibetan Plateau through China’s Yunan Province, Burma, Thailand, Laos, Cambodia and Vietnam.
Pangasius is a large sized freshwater catfish (2nd in rank after Mekong Giant Catfish (Pangasianodon gigas). The biggest size that had been found was 150 cm in length. Its origin is in India and Burma and then distributed in Thailand and Indonesia. In Thailand, It is found in some rivers, reservoir, swamps and river-system in the Central Mekong River. It is mostly found in area where aquatic plants are abundant.
In the Philippines, Pangasius was introduced by private sectors usually petshop owners in 1978 and subsequently by Mr. Tapiador (1981) from Food Agricultural Organization (FAO) which has bought this fish to the Bureau of Fisheries and Aquatic Resources (BFAR) from Thailand for experimentation.
Pangasius has a scaleless skin with quite long slender body with black to dark gray on the dorsal portion and light gray on i the lateral side and whitish on the abdominal portion parallel along the’ lateral line total body length is 4-5 times head length and standard length almost/nearly 4-5 times of body width.
With the wide mouth and curvature (not sharp) located in quite low position has the ability to feed on a variety of food items (omnivorous). Two(2) pairs of barbells are situated in the mouth one pair on the upper jaw (maxillary barbell) and one pair on the lower jaw (mandibulary barbell) which the first pair is longer than the latter.
The fins are classified into dorsal, caudal, adipose, ventral and anal fin. The dorsal fin consists of one hard fin ray (spine like saw) and six (6) soft fin rays. An adipose fin is situated between the dorsal and caudal fin. The caudal fin is isocoercal and anal fin consists of four (4) hard rays and 30-32 soft fin rays. The pectoral fin composed of eight to nine (8-9) soft fin rays.
d. Sexual Dimorphism and Breeding
Under normal conditions Pangasius becomes sexually mature during the 2nd year. In some ponds where conditions are not favorable to this growth the period is considerable longer.
A gravid female have a bulging belly which is swollen and soft while the urogenital-oval shape is reddish in color which is much bigger than the male. The release of yellow eggs is eminent when abdomen is pressed or when holds at the caudal and fold its body above water. While the male have a slender body and belly is not swollen. The urogenital-oval shape is narrow and smaller than the female and when the belly is pressed, it releases white milt.
The spawning season for Pangasius coincides with the monsoon rains. Hatching period is from 27-32 hours after spawning at temperature of 28-31°C. The fertilized eggs are sticky and spherical in shape. It is 1.186 mm in diameter, contains large quantity of yolk and has a yellow greenish color. The newly hatched fry which is approximately 3 mm in length is colorless and transparent with no signs of motility from 1-2 hours then after, it swims in vertical direction until 3 days old After absorption of the yolk sac, the freshwater hammerhead shark fry differs from other fish that it will begin to eat food and has & cannibalism behavior since the mouth has just opened The 3 days old fry can swim horizontally and organ will completely developed as the mature fish reaches its 14 days.
Induced Breeding and Artificial Propagation of Pangasius
Artificial propagation of fish or inducing the fish to spawn by injection of hormone is a technique referred to in aquacultural parlace as “hypopysation”. This technique is usually done due to the absence of ecological conditions in confined environment (i.e. ponds and cages), which can not meet the propagation requirements of the broodfish. Thus, Aquaculturist can estimate his production and plan his work well advanced.
Reproduction in all fishes is controlled by hypothalmo-pituitary gonad axis. The pituitary secretion activity is, in turn mainly controlled by relative external factors through the nerved center. To explain this in detail, when .certain ecological condition (i.e. rainfall, temperature, photoperiod, water current, etc.) stimulates the external sensing organ of the fish (i.e. lateral line, skin, visual and auditory organs) the nerves of these external sensing organ produced impulses which are immediately sent to the nerve center and transmitted to the pituitary gland. When the pituitary gland has been excited by the stimulation, it answers or reacts by secreting gonadotrophic hormones.
Those hormones are transmitted by body fluids and cause certain physiological changes when the hormones reach the gonads. the gonad in turn become stimulated and begin rapidly to develop and mature. Ovulation begins and simultaneously a sex hormone is secreted. This sex hormone acts in coordination with the gonadotrophic hormone and in active sexual activities like laying eggs and exuding milt.
The basic principles of artificial estrualization rest on the general biological principles of natural propagation of fish. Because of the shortcomings of the ecological condition in controlled and semi controlled conditions (i.e. ponds, cages, tanks, etc.) which can not meet the propagation requirement of the broodfish artificial methods of exogenous application of gonadotrophic hormones (pituitary gland or chorionic gonadotropin) which mimic the endogenously secreted hormone. These injections supplement the secreting function of the pituitary gland in the live body; on the other hand, they also hasten the secreting activity of the pituitary gland and thus induced the broodfish to lay eggs or exude milt.
Pangasius egg maturation and ovulation do not occur under captive condition hormonal injection is necessary.
Pituitary Gland Induction (PG)
- Fresh pituitary gland of a fully mature catfish species is needed and for the female the amount of pituitary gland solution to be administered is one dose and 2 doses for the second injection with 12 hours interval time.
Injection of hormone is done intramusculary between the base of dorsal fin and lateral line near the caudal peduncle. Ovulation will take place between 10-12 hours after the second injection at temperature of 28-32Â°C. Ovulating female is stripped off its egg.
This is done by wiping excess water from the fish and applying pressure to the abdominal area allowing the eggs to flow freely into the receiving dry basin. The male is simultaneously stripped off its milt and fertilization is facilitated by gently mixing the eggs and sperm using a chicken feather.
At the temperature of about 28-32° C, fertilized eggs hatch out in 24-36 hours and two (2) days after hatching, yolk sac is almost absorb and the fry will start to feed.
On the third day the fry are transferred to a nursery pond to avail of the natural food present in the pond.
Prior to the actual breeding, a week before, the pond where the nursery hapa will be installed is fertilized with organic fertilizer at a rate of two (2) tons per hectare to allow the growth of planktons. Aside from the natural feed present, fry are fed with water flea (“moina”) continuously for one (1) week. After ten (10) days the fry are given supplemental feeds with a mixture of fishmeal (40%) and ricebran (60%) with crude protein content of 35% at 5% body weight twice a day continuously for 31 days.
For more information and questions, contact:
Dr. Adelaida L. Palma
BFAR-NIFTC Tanay, Rizal
Email: [email protected]