DISEASES OF STRIPED RIVER CATFISH, Pangasius hypophthalmus CULTURED IN SUNGAI PAHANG AND SUNGAI PERAK, MALAYSIA  

Pangasius sp is a valuable catfish species extensively cultured in Southeast Asia. The species was introduced in Malaysia the 1980s, and is the largest species cultured after carp and tilapia (FAO, 2009). Locally known as patin, the species is widely cultivated in Sungai Pahang. Pangasius sp has been reported to be  susceptible to bacterial diseases such as bacillary necrosis caused by Edwardsiella ictaluri (Crumlish et al., 2002) and Aeromonad Septicemia caused by Aeromonas hydrophila (Ferguson et al., 2001;Subagja et al., 1999).

Continuous reports of high mortality of Pangasius sp cultured in Sungai Pahang since 2008 with mortality rate almost 30-40% especially during the dry season led to a thorough study to determine the primary etiology causing mortality of Pangasius sp and to relate the problem with water quality through monthly sampling. Aeromonas hydrophila infection (3.1%) with clinical signs of inflammation around mandibles, basal fins and ventral regions was detected. Water quality parameters showed no significant findings. Histopathological changes showed necrosis and hemorrhages in kidney and liver while spleen was severely congested and hemorrhagic. There was focal encephalitis with infiltration of mononuclear cells, particularly around the ventricle and blood vessels, suggesting viral infection. Following PCR detection for channel catfish virus, the etiological agent was confirmed to be channel catfish virus (CCV). This finding was the first reported CCV infection in striped catfish (Siti-Zahrah et al., 2013).

Since most of Pangasius sp fry comes from the state of Perak, similar study was conducted but the number of farmers culturing Pangasius sp in Sungai Perak were comparatively much lower, which could be why less disease problem reported as in Sungai Pahang. Three month sampling of the fish cultured showed that the fish appeared healthy with minimal clinical signs. However, internal organs showed enlargement of the kidney and spleen with occasional appearance of white and black nodules in the spleen. Bacterial isolations revealed the presence of Aeromonas sp (12%) and Edwardsiella tarda (4-12%).  This initial finding could be of potential disease problem later, especially when the immune system is being compromised by stress factors especially during dry season.