Maehongson Inland Fisheries Station, Inland Fisheries Division, Department of Fisheries, Thailand
ABSTRACT
Shovelnose catfish (Aorichthys seenghala) is an endemic species found in the Salveen River and its tributaries. The Salveen River originates in the eastern Himalayas. This popular fish is easy to catch and hence to overfish. In 1996 the Thailand Department of Fisheries initiated a programme of breeding this species in captivity. The programme has succeeded to spawn the fish in earthen and concrete tanks, and to grow them to a size of up to 250 g in 20 months.
ASIAN SHOVELNOSE CATFISH (Aorichthys seenghala)
Asiatic shovelnose catfish is an endemic species found in the Salween River and its tributaries. The Salween River originates in the Tibetan range of the eastern Himalayas and passes the Thai - Myanmar border and runs off to the Andaman Sea. In Thailand, the main stream has three large west draining tributaries, the Pai River at Mae Hong Son and the Moei River at Tak (both in the northern region), and the Suriya - Maekasat River in the Thungyai Wildlife Sanctuary, Kanchanaburi, in the western region. The status of this species is more or less "endangered" due to the poor knowledge of its biology, but also due to the declining stocks of this fish in natural waters. The large size and a long period of 4 to 5 years required to reach maturation contribute to this decline. It has been one of the popular species to capture due to the tasty flesh, high price when marketed, easy to catch and therefore overfish. In 1996 the Thailand Department of Fisheries set up a programme of breeding this fish at the Maehongson Inland Fisheries Station.
General biology
Asiatic shovelnose catfish or "Pla Kot Hua Seum" is one of the catfish in the family Bagridae. The species is easily recognized by its very broad, flat and long head with smooth upper surface, and the grayish or green back and sides. The largest fish captured was 100 cm long, with a body weight of 5 kg. In the Pai River, Maehongson Province, this species spawns during the cold season from January to April. It spawns at the edge of the shore at about 1 - 2 m below the surface. It excavates a sand-gravel hole near a rock, about 1 m in diameter and 30 cm deep, in which the female lays eggs and take care of the fry.
Collection and feeding of broodfish
The fish is captured in the Pai River, Maehongson Province, Thailand using hook-and-line, cast nets, gill nets and seines, and is then transported to the Maehongson Inland Fisheries Station. The captured fish are released in 2 400 m2 earthen ponds. Males and females are separated, each in different ponds. Broodfish do not adapt to formulated feed because they are extremely predatory. Fingerlings of carps and rohu are fed at 0.5 - 2.0% body weight once a day. Sex can be distinguished by the shape of the genital papilla. In the male, the genital papilla is pointed and the fish has a slender body. The female papilla is oval and a mature fish has a big belly full of eggs. Its abdomen becomes distended at spawning time. The cloaca is reddish and prominent. Males should be at least 60-80 cm in total length and 2.0 - 2.5 kg in body weight, while females should be 80-100 cm in total length and 3.0 - 4.5 kg in body weight.
Natural spawning methods
Spawning ponds can be either earthen or concrete. In an earthen pond, the size should be around 800 m2 with a water depth of 1-1.5 meters. The pond should have a deeper section at the outlet to assist in fry harvesting. Ponds were prepared by liming with calcium hydroxide at the rate of 1 kg per 25 m2 and water was filled to a depth of 1 m at the time of stocking. During January to April, broodfish were stocked at the rate of 5 pairs per pond. The pond was drained 4 months after stocking and 5 depressions with diameters of 57-98 cm and 8-23 cm deep were found in the bottom. 1 834 fingerlings with 5 different sizes from 3 to 11 cm total length and 1 to 10 g body weight were collected. Males were found to lose their skin mucus and the color of body changed from grayish back and whitish sides to reddish.
A concrete pond with the a of 50 m2 with a minimum 50-70 cm water depth can also be used for spawning of the Asiatic shovelnose catfish. The pond's bottom must be carefully covered with sand and gravel to approximately 10-30 cm thickness and filled with aquatic plants as in natural habitats. There should be continuous flow of water through the pond at a rate of 10 L per minute. Broodfish are stocked at a rate of 5 pairs per pond during January to April. The pond was drained 4 months after stocking and 563 fingerlings of 2-3 cm total length and 1-3 g body weight were found in 90 cm diameter and 8-23 cm deep holes in the bottom at the corner of the pond. Only one male showed sign of losing its skin mucus and changing the color of its body from grayish back and whitish sides to reddish.
Following spawning, males protected their nest and fed their young with their own skin mucus until the fry reached fingerling stage. At this stage the fingerlings became predatory and cannibalistic. Spawning of broodfish stocked in earthen and concrete ponds during May to August and September to December is unreliable.
Hormonal induced spawning methods
Artificial spawning of the Asiatic shovelnose catfish by using synthetic luteinizing releasing hormone in combination with dopamine antagonists has not been successful.
Nursing and rearing of fingerlings
Fingerling, at a stocking rate of 50 fish per m2, can be nursed in 20 m2 concrete ponds supplied with a continuous 10 L per minute water through-flow. Fish were fed twice daily to satiation with 35-40% protein complete feed. After 30, 60 and 90 days, the total length of fingerlings was 5-7, 7-10 and 10-15 cm, and body weight was 1-3, 3-7 and 7-15 g, respectively. The survival rate was about 70-90%.
The Asiatic shovelnose catfish can also be nursed in cages at the rate of 100 fish per m3 and fed to satiation with 30-35% protein complete feed twice daily. After 8 and 20 months, the total length of fingerlings was 25-30 and 33-35 cm, and body weight 70-100 and 200-250 g, respectively. The survival rate was 80-95%.
These results are only preliminary and have showed that the Asiatic shovelnose catfish can adapt from its natural habitat to a captive environment and can spawn in captivity.
