Aquatic Animal Health Research Institute
Department of Fisheries
Kasetsart University Campus
Jatujak, Bangkok 10900, Thailand
Chinabut, S. 2002. Jaundice disease in catfish, a case study demonstrating a decline in incidence as a result of research output. p. 77-80. In: J.R. Arthur, M.J. Phillips, R.P. Subasinghe, M.B. Reantaso and I.H. MacRae. (eds.) Primary Aquatic Animal Health Care in Rural, Small-scale, Aquaculture Development. FAO Fish. Tech. Pap. No. 406.
The catfish cultured in Thailand is a hybrid of the male African catfish, Clarias gariepinus, and the female of the native catfish C. macrocephalus. Farmers were initially using chicken offal as a substitute for trash fish or commercial pellet because the market price for catfish had reduced. A severe outbreak of catfish jaundice was reported in the summer of 1992 that caused 20-100% mortality. The economic loss due to this disease was estimated at US$360-1,800/farm or US$4.3-21.3 million for the whole country. Research indicated that rancid chicken offal was the cause of this disease. Farmers were advised to improve the quality of the chicken offal and the water quality in the ponds, and, subsequently, the incidence of jaundice declined dramatically. Recommendations based on research resulted in improved fish health and reduced economic loss due to disease.
Catfish culture in Thailand has been developed for more than half a century, and the walking catfish (Clarias batrachus) was the species first cultured in ponds. After success in induced spawning and mass production of the seed of C. macrocephalus, another native catfish, this species became more popular, as it has a more palatable taste. However, this species is slow growing and susceptible to many infectious diseases. Following this, the African catfish, C. gariepinus, which is a fast-growing species, was introduced into Thailand; however, the flesh is not firm and aquaculturists, therefore, attempted to cross breed these three species to obtain a hybrid with better qualities. Finally, the ideal hybrid catfish was developed by cross breeding male African catfish and female C. macrocephalus. Since then, farmers have cultured culture only the hybrid catfish because of its better taste and faster growth.
Hybrid catfish fry can grow from1-2 gm to 200-300 gm within a four-month culture period. Trash fish, commercial pellets or a combination of these two feeds has been used routinely in catfish farms. Successful catfish culture resulted in an over-supply of the product on the market, causing a decrease in the wholesale price. Farmers, therefore, needed to reduce production costs, the major cost being feed. Some farmers began to use chicken offal from the processing plants as a supplementary feed. They found that catfish fed in this manner developed a light yellow colour on the body, similar to that of the preferred C. macrocephalus, and, that as a result, they obtained a better price in the market. The exclusive use of chicken offal increased as the market price of catfish fell. Offal was transported from the factory in un-refrigerated lorries and could take many hours to reach its destination. Some feed was kept overnight for the following days' feeding programme and, when temperatures were high, the feed was likely to become rancid before it was fed to the fish.
Jaundice is yellow coloration of the skin and other tissues due to an excess of bile pigment present in the blood and lymph. The condition described in catfish as "catfish jaundice" was first observed in central Thailand in early 1990, and by the summer of 1991, several farms reported the problem in fish over four-five months of age. In 1992, signs of jaundice were observed from March onwards in fish over four months of age. Affected fish usually ranged from 150-350 gm, which is the market size. Eighty percent of affected farms were using chicken offal as the only source of feed in an attempt to decrease feeding costs. The first indication of the disease was that farmers observed reduced appetite and the fish became lethargic. Following this, the fish became anorexic, and clinical signs of jaundice were observed. Mortality rates increased and, in some cases, over 90% of affected fish on the farm died. Jaundiced fish proved more susceptible to stress and tended to die before they got to the market.
When farmers have problems, they contact local fisheries officers, nearby diagnostic laboratories, or the salespersons who supply them feed or chemicals. For simple cases, the problem can be solved at the site or through a telephone discussion with a disease expert. In the case of a new disease, with which they have no experience, such as jaundice in catfish, they require the services of the staff at the central laboratory (the Aquatic Animal Health Research Institute, AAHRI), where investigation and research can be carried out. With the close relationship between the diagnostic service, farmers, fisheries officers, salespersons and researchers, problems can be effectively researched and solutions found. Research conducted at AAHRI is generally initiated by problems that occur on farms.
Affected fish showed yellow colour of the skin and gills. By the time the fish showed clinical signs, they were usually anorexic and moribund. Gill rot was a frequent finding. The spleen, kidney and liver were enlarged and a pale-yellow colour. The gall bladder was also enlarged, with yellowish bile. Most fish had a yellow ascitic fluid, which, on exposure to air, solidified faster than ascitic fluid from other septicaemic fish. The fat tissue in the abdominal cavity was also yellow in colour.
No bacteria, viruses or fungi of known pathological significance were consistently isolated from any of the fish sampled.
Serum from jaundiced fish was bright yellow to orange in colour. Haematocrit levels from jaundiced fish were markedly reduced (10-16%) from normal (34-37%).
The most obvious pathological changes were observed in the liver, kidney and spleen. Examination of the livers revealed varying irregular vacuolation of the cytoplasm of the hepatocytes; however, catfish livers tend to be highly vacuolated, so this was within the normal range of variance. Two types of pigment were found as deposits in the liver. One was amber in colour and scattered intercellularly throughout the liver parenchyma and also within the lumen of the bile duct and blood vessels. In addition, a lighter yellow-brown pigment, with a more granular texture, was observed accumulated in the macrophages, which were in clumps associated with the portal vessels.
Pigment deposits were also widespread throughout the haemopoietic tissue of the kidney and spleen. Large accumulated deposits of yellow-brown pigment were observed within macrophages associated with the melanomacrophage centres of the spleen. Intracellular pigment was observed in individual cells scattered throughout the pulp. Degenerative changes in the cells associated with the melanomacrophage centres were observed in some sections.
Kidney sections revealed the presence of amber pigment within the tubule lumen. Deposits of intracellular pigment of varying size were observed scattered throughout the haemopoietic tissue within individual cells and clumps of cells. Protein droplets had accumulated in the epithelial cells lining the renal tubules. Degeneration of the tubule walls was observed in some samples.
These pigments were identified as ceroid and haemosiderin. Ceroid is a brown-yellow, acid-fast, lipid-positive pigment, resistant to organic solvents, which accumulates in the livers of fish during lipoid liver degeneration (LLD). Haemosiderin is a breakdown product of haemoglobin.
Results from farm information and pathological investigation indicated that the fish were suffering from a haemolytic anaemia and jaundice. The cause of the disease was thought to be nutritional in origin, due to the feeding of rancid chicken viscera. Therefore, an experimental trial was conducted. Five groups of catfish were fed with different types of feed as follows: 1. fish pellet, 2. chicken offal kept in the refrigerator during transportation and before use, 3. rancid chicken offal with fish pellet, 4. rancid chicken offal with vitamin E, and 5. rancid chicken offal. The results demonstrated that catfish fed with rancid chicken offal developed jaundice disease.
Rancid fats in the diet result in high levels of free radicals and peroxides that cause oxidative damage to biological membranes and organelles. Polyunsaturated fatty acids (PUFAs) are essential components of all biomembranes. Fish tissues typically contain large quantities of highly unsaturated series fatty acids and may be more at risk from peroxidative attack than are mammals. Vitamin E is an important antioxidant and protects biological membranes from lipid peroxidation by acting as a scavenger of free radicals. The presence of rancid fats however depletes the diet of vitamin E and other antioxidants, leaving the biological membranes vulnerable to oxidation.
All kinds of media were used to disseminate information to the farmers: articles in newsletters and radio and television programmes on agricultural news. Fisheries extension officers are the other vehicle for transmission of the message directly to the farmers, as they normally work closely together. Therefore, the results of this study were communicated to the farmers, with advice to be careful regarding the quality of chicken offal, or to use chicken offal along with fish pellets, to prevent jaundice disease.
After 1993, the incidence of jaundice disease in catfish declined dramatically to almost zero percent, as farmers improved the quality of the feed as recommended. This case study demonstrates that results from research work can quickly reach farmers and help prevent losses caused by disease.
The size of catfish farms in Thailand is very variable, the smallest being one pond of 400 m2; however, the average size of ponds is 1,600 m2. Production after 3-4 months is 20 (16-24) mt/1600 m2 (125 (100-150) mt/ha) and the price is US$0.6/kg. During the outbreak of jaundice in catfish in 1992, average production declined significantly, even though the number of farms operating increased to 11,855 farms (Table 1). Loss due to jaundice disease was 20-100%. Based on fisheries statistics, the average production of catfish between 1988-1995 was 3 (2-4) mt/farm. Therefore, the economic loss due to this disease was US$360-1,800/farm or US$4.3-21.3 million for the whole country.
Table 1. Production of cultured hybrid catfish in Thailand between 1988-1995.1