Sustainable aquaculture A perspective on breeding and genetics of walking catfish in Thailand Uthairat Na-Nakorn Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand 10900 Dr. Uthairat Na- Nakorn is a Professor at the Kasetasrt University of Thailand. She is the Head of the Genetics Laboratory in the Faculty of Fisheries. What is walking catfish? resulting in higher yield per unit area in paddy. Small and shallow ditches were a shorter culture period than C. dug along the field to create Walking catfish, or “pla dook” in Thai macrocephalus (19-60 t/ha within 4 rectangular platforms approximately 3 is a common name for a group of months for C. batrachus vs 6-19 t/ha in metres wide. Holes of 20-30 cm in Clarias species that are distributed 6-8 months for C. macrocephalus)4. diameter and 20 cm deep were dug at 1 throughout south, eastern and The breeding techniques for C. m interval throughout the platforms. southeastern Asia and Africa. There are batrachus were developed using local Then grass was allowed to grow at least five Clarias species that knowledge of farmers. The breeding naturally. Around mid February inhabit rice paddies and marshes method described here was reported by brooders of mixed sexes were stocked across Thailand1, amongst which C. Sitasit5. However, it has not been into the large ditch while the rest of the macrocephalus and C. batrachus are widely practiced since 1987 due to the pond was exposed. After 2-3 weeks or the most common. Walking catfish are replacement of Clarias batrachus in whenever water was available, ponds the main ingredient for Thai dishes the culture system by the hybrid. were flooded. The flooding of the such as pla dook foo (crispy deep fried The breeding farms producing C. previously exposed soil coupled with - grilled walking catfish meat), batrachus are confined mainly to the holes and available grass roots phaadpet pla dook (stir fried walking Samutprakarn area where rice paddies stimulated spawning. Each pair of male catfish in chilli sauce) or grilled walking (1-2 ha) were modified by digging and female fish occupied a hole and catfish that is always accompanied by ditches 2-3 metres deep and 3 metres spawned shortly after flooding. The the famous papaya salad somtam. wide around the inner sides of the rice whole system was left untouched for a History of catfish culture in Thailand Aquaculture of Clarias in Thailand has been expanding and current annual production is approximately 82,000 mt worth US$52 million by value2, comprised mainly of hybrid catfish (Clarias macrocephalus x the introduced African sharp-tooth walking catfish, Clarias gariepinus). In the past, the supply of walking catfish came solely from the wild catch. Since 1960 Thai farmers have developed breeding and culture technologies for C. batrachus3 despite its relatively lower preference to Thai consumers compared to C. macrocephalus. Clarias macrocephalus and C. batrachus. The distinct difference is shape of skull Farmers produced C. batrachus (arrows): the occipital process of Clarias macrocephalus is round while that of C. because it was hardy and grew faster batrachus is pointed. 10 Sustainable aquaculture systems. C. batrachus was stocked in earthen ponds of approximately 0.3-2 80 ha. The catfish were fed trash fish mixed with rice bran and water was 70 changed occasionally. The culture 60 system was not hygienic due to extremely poor water quality. However, 50 the fish are able to tolerate extreme 40 conditions of low oxygen due to 30 accessory air breathing organs in the gill cavity. Although extremely high 20 yield per unit area was achieved, 10 culture of C. batrachus was rather risky due to frequent disease outbreaks 0 and its low price during the outbreak. 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 Successful commercial artificial breeding of C. macrocephalus was Fig.1 Annual production of catfish from aquaculture in Thailand from 1990-2000 (unit: 1,000 mt). achieved around 1985, some 25 years after the technology was developed in a laboratory6. Despite the successful production of fry and the high price of the species, culture of C. macrocephalus was limited by several factors including slow growth, disease outbreaks, and a remarkably low yield compared to C. batrachus4. Genetic approaches to improve quantity and quality of production Attempts to improve performance of C. macrocephalus with the application of genetic principles had generally failed. Selection programs were established based on individual’s phenotypes (“mass selection”). Although efficiency of this method is usually low, it 3mditch spawning hole shallow ditch requires less facilities and resources A compared to other techniques such as “family selection” in which many families of fish have to be separately maintained. Mass selection to improve pond bank growth rate of C. macrocephalus gave positive results with improvements of 11.8% by weight and 2.3% by length achieved after three generations7. However the program was not pursued further. Mass selection for disease resistance (i.e. to Aeromonas B hydrophila) was carried out at the A diagram showing a typical Clarias batrachus breeding pond: a) top view, b) cross Department of Aquaculture, Faculty of section Fisheries, Kasetsart University and resulted in improved survival rate after period of 9-12 days until fry were seen. produced approximately 125,000- disease challenges8. The program was If sufficient amount of fry was 2,200,000 fry/ha. terminated after only two generations observed the water level was lowered During that period aquaculture due to mass mortality of the selected until the breeding holes became production of Clarias was primarily C. fish caused by other pathogens. It is partially exposed and fry were collected batrachus. The culture area was mainly likely that response from mass by scoop-net. Each breeding cycle in Suphanburi, a province west of selection declined in successive Bangkok that has extensive irrigation generations due to a reduction of October-December 2004 (Vol. IX No. 4) 11 Sustainable aquaculture variance of traits, or overwhelmed by isolated habitats. References negative correlated response and/or Besides the destruction and rapid inbreeding9. alteration of habitats, impacts of the 1. Inland Fisheries Division, 1970. Fishes of The Family Clariidae Found in Thailand. Department of Chromosome manipulation hybrid between C. macrocephalus and Fisheries, Bangkok. techniques were also employed to C. gariepinus that escaped from farms 2. DOF, 2003. Fisheries Statistics 2000. Department of Fisheries, Bangkok. improve growth rate by inducing to natural waters in all probability 3. Csavas, I., 1994. Status and perspectives of culturing triploid sterility. Surprisingly, the accelerated and or contributed to a catfishes in east and southeast Asia. Review paper presented at the International Workshop on growth rate of triploid C. reduction of abundance of native Biological Bases for Aquaculture of Siluriformes, 23- macrocephalus did not improve over catfishes. The hybrid may have out- 27 May, 1994. Montlellier, France. that of the diploid counterpart despite competed the native species due to its 4. Na-Nakorn, Uthairat. 2001. Walking Catfish; Breeding and Culture. KU Press, Bangkok. (In Thai) 10 its sterility . Induction of gynogenesis aggressive feeding behavior. More 5. Sitasit, Prasert. 1981. Local method for breeding and produced all female C. macrocephalus11, 12 seriously, introgression of C. nursing of Clarias batrachus fry. Thai Fisheries Gazette 34(3): 327-336. (In Thai) which was preferable due to presence gariepinus genes into genomes of C. 6. Na-Nakorn, U., 1982. History of aquaculture in of eggs at harvest. However, the macrocephalus has been detected in Thailand. Thai Fisheries Gazette, 36(1), 24-31. (In 16 17 Thai) technique was not commercially central Thailand and in other areas . 7. Jarimopas, P.,Kumnan, A., Wongchan, J., 1989. Mass feasible due to the low hatching rate of Such introgression can eventually lead selection of Clarias macrocephalus Gunther for the gynogenetic fry. to extinction. growth. pp.177-191, in Final report, Fish Genetics Project (Phase II). National Aquaculture Genetics A turning point in catfish farming in Attempts have been made to Institute, Bangkok. Thailand, from a production view point, sterilize the hybrid by induction of 8. Na-Nakorn, U., W. Rangsin and S. Witchasunkul. 18 1993. Suitable conditions fort Induction of was reached when the sharp-tooth triploidy . Unfortunately the triploid gynogenesis in the catfish, Clarias macrocephalus African catfish Clarias gariepinus was hybrid was not completely sterile and eggs using sperm of Pangasius sutchi. Aquaculture, 118: 53-62. introduced in 1987. It was not well growth performance did not improve. 9. Falconer, D.S., 1983. Introduction to Quantitative accepted by consumers because of its Until now no measures have been Genetics 2nd ed. Longman Group Limited, New York. unfamiliar features and poor flesh undertaken to avoid further adverse 10. Na-Nakorn, U., Lakhaanantakun, A., 1993. Comparison between the performance of diploid and texture. Subsequently, it was impact of the hybrids on biodiversity. triploid Clarias macrocephalus. pp. 79-86, In Fish hybridized with the native C. Genetics and Its Application to Aquaculture and Fishery Management. BIOTROP Spec. Publ. No. 52. macrocephalus to improve growth and Further Studies 11. Na-Nakorn, U., Chantsawang, S., Tarnchalanukit, W., disease resistance of the latter. The 1993. Response to mass selection for resistance to Aeromonas hydrophila in Clarias macrocephalus. hybrid with maternal genome from the It would be extremely difficult to J. Appl. Aqua. 4 (4): 65-74. native catfish showed improved growth suddenly stop farmers from culturing 12. Na-Nakorn, U. 1995. Comparison of cold and heat rate over C. macrocephalus although the hybrid catfish in Thailand. shocks to induce diploid gynogenesis in Thai walking catfish (Clarias macrocephalus) and no significant heterosis was Aquaculture of the hybrid can be performance of the gynogens. Aquatic Living observed13.