Color profile: Disabled Composite Default screen 7 Infectious Diseases of Warmwater Fish in Fresh Water Gilda D. Lio-Po1 and L.H. Susan Lim2 1Aquaculture Department, Southeast Asian Fisheries Development Center, Tigbauan, 5021 Iloilo, Philippines; 2Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia Introduction (Hypophthalmichthys molitrix) together with Puntius gonionotus and Leptobarbus Cage culture of freshwater fish, which hoevenii dominate the cyprinids (Table 7.1). began in Cambodia in the late 1800s, is now Due to the variety of common names avail- commonly practised in Southeast Asia and able for a particular fish species in Southeast gaining popularity in India (Chapter 1). In Asia, the scientific names will be used as developing tropical countries, this type of much as possible. fish culture is still either at the subsistence Publications and reports are available or semi-intensive level or is at the experi- on diseases of feral and cultured fish in mental stage, as for Chrysichthys spp. in warm fresh water (Lio-Po, 1984; Kabata, Africa (Aqua Farm News, 1993). 1985; ADB/NACA, 1991; Lim 1991d, 1992; Fish cultured in cages in Southeast Asia Paperna, 1991, 1996; Arthur, 1992; Thune include tilapia, carp, catfish, snakeheads et al. 1993; Arthur and Lumalan-Mayo, and eleotridids (Table 7.1). The tilapias, one 1997; Fijan, 1999). However, there is a of the common species in freshwater cages, paucity of information on diseases of fish are also cultured in cages in warm marine in freshwater cage culture, even though waters (Chapter 6) (Aqua Farm News, 1993). cage culture began in Southeast Asia The catfish cultured include the Ictaluridae (Chapter 1) (Christensen, 1989; Aqua Farm (Ictalurus spp.), Claridae (Clarias spp.), News, 1993). Diseases are normally either Pangasiidae (Pangasius spp.), Siluridae mentioned in passing or are not included, (Silurus glanis) and Bagridae (Hemibagrus particularly in those publications dealing spp.) (Aqua Farm News, 1993). Most catfish with cage culture (Christensen, 1989; are of Southeast Asian origin, the exception ADB/NACA, 1991; Dharma et al., 1992; being channel catfish cultured in the Nasution et al., 1992; Alawi and Rusliadi, USA, which have been introduced into 1993; Aqua Farm News, 1993). In addition, cages in Indonesia (Rabegnatar et al., 1990). publications on diseases in fish culture The most common catfish species cultured do not distinguish between diseases in cages in Southeast Asia is Pangasius found in cage culture and pond culture hypophthalmus. Exotic Chinese carp, (Davy and Chouinard, 1982; Arthur, common carp (Cyprinus carpio), grass 1987; ADB/NACA, 1991; Aqua Farm News, carp (Ctenopharyngodon idellus), bighead 1993). This is further exacerbated by the carp (Aristichthys nobilis), silver carp lack of comprehensive investigation into ©CAB International 2002. Diseases and Disorders of Finfish in Cage Culture (eds P.T.K. Woo, D.W. Bruno and L.H.S. Lim) 231 241 Z:\Customer\CABI\A4337 - Woo\A4419 - Woo Vouchers.vp Tuesday, November 05, 2002 11:35:09 AM Color profile: Disabled Composite Default screen 232 G.D. Lio-Po and L.H.S. Lim Table 7.1. Freshwater fish species cultured in cages in some tropical countries. Country Fish species References Bangladesh Catla catla Karim and Harun-al-Rashid Khan (1982) Cirrhina mrigala Cyprinus carpio Hypophthalmichthys molitrix Oreochromis niloticus Cambodia Channa micropeltes Thana (2000) Cirrhinus microlepis Labeo sp. Clarias sp. Guerrero (1979) Leptobarbus hoevenii Oxyeleotris sp. Pangasius sp. India C. catla Natarajan et al. (1983) C. mrigala Labeo bata Labeo rohita Channa striata Sukumaran and Sanjeeviraj (1983) Oreochromis mossambicus Jameson (1983) Indonesia C. striata Indra (1982) Oxyeleotris marmoratus Tilapia C. carpio Jangkaru and Rustami (1979) Malaysia Aristichthys nobilis Annual Fisheries Statistics (1998) C. striata Ctenopharyngodon idellus C. carpio Hemibagrus nemurus (also known as Mystus nemurus) H. molitrix L. hoevenii O. marmoratus Puntius gonionotus Tilapia Philippines A. nobilis Palisoc (1988) Chanos chanos C. carpio H. molitrix O. niloticus Sri Lanka O. niloticus Siriwardena (1982) Thailand Clarias spp. Tugsin (1982) C. carpio Goby sp. O. niloticus Vietnam Barbus spp. Pantulu (1979) Leptobarbus sp. C. striata T.T. Dung (personal communication) O. marmoratus Pangasius bocourti Pangasius conchophilus diseases encountered in cage culture sys- Disease outbreaks in cage culture have a tems in warm waters. greater impact because of high stocking 242 Z:\Customer\CABI\A4337 - Woo\A4419 - Woo Vouchers.vp Tuesday, November 05, 2002 11:35:10 AM Color profile: Disabled Composite Default screen Infectious Diseases of Warmwater Fish in Fresh Water 233 densities and close proximity of cultured affected. Most viral infections occur in fish with each other as well as with feral fish. fish at low water temperatures. This may For example, there were 64 reported disease explain the paucity of viral infections outbreaks in cage-cultured channel catfish recorded in warm freshwater fish. Stress in the USA during 1990 with mortality from handling, poor water quality, water in 91% of these cases (Masser et al., temperature, age of fish, high stocking 1991). Also, diseases appear to occur more density and poor nutrition are factors frequently in cages than in ponds (Collins, that facilitate the development of viral 1988). Cage culture exposes fish to diseases. pathogens of feral fish and perhaps to a Among viral infections in fish, the greater number of intermediate hosts in channel catfish virus disease has the most parasitic diseases. Fish reared in cages may impact on cage culture while the grass carp also present a potential health threat to haemorrhagic virus and the spinning tilapia man, especially when they are reared in syndrome are also potential viral problems. unsanitary waters in areas where fish-borne In addition, other viral epizootics have been zoonotic diseases are prevalent (see reported in common carp and tilapia that Ko, 1995) or when located in polluted may have implications in fresh warmwater areas. Diseases afflicting pond-reared and cage culture systems (Sano et al., 1993; cage-cultured fish are in most cases similar, Oyamatsu et al., 1997; Fijan, 1999). hence those that are important in pond The epizootic ulcerative syndrome (EUS), aquaculture will be treated as potential a disease associated with a rhabdovirus, problems for the cage culture. For example, bacteria and the pseudofungi, Aphanomyces Piscinoodinium pillulare, the causative invadans, is discussed in the section on agent of velvet disease of cyprinids, was first Diseases of Complex Infectious Aetiology. reported on pond-reared fish but is now An insufficient number of susceptible found on cage-cultured fish (F. Shaharom, fish cell lines hampers isolation and diagno- personal communication). The paucity of sis of viral pathogens. Cell lines currently information on diseases in cage-cultured used for isolation of warm freshwater fish is partly due to the lack of studies on virus are from: bluegill fry (BF-2) (Wolf identification of pathogens/disease mecha- and Quimby, 1966), brown bullhead (BB), nisms and/or the absence of mandatory channel catfish ovary (CCO) (Bowser and reports on disease outbreaks in many Plumb, 1980), Epithelioma papulosum countries. Hence, we expect diseases to cyprini (EPC) (Fijan et al., 1983), grass carp become more prevalent in the future as we kidney (GCK-84), grass carp gonad (GCG), move into more intensive fish culture, grass carp fin (GCF) (Wolf, 1988), rainbow find out more about infectious agents, and trout gonad (RTG-2), snakehead fry (SSN-1) adopt a system where it is mandatory to (Frerichs et al., 1993), catfish spleen (CFS) report disease outbreaks. In the current and snakehead spleen (SHS) (Lio-Po et al., review, we have also included unpublished 1999). information from colleagues as well as Electron microscopy for the diagnosis from personal observations, and wherever of viral infections is not commonly used possible we have provided the correct iden- due to inaccessibility to this equipment in tification of pathogens and supplementary most tropical countries. As an alternative, information on them. serological tests are applied such as neutral- ization index determination, Western blot, ELISA, fluorescent antibody technique Viral Infections (FAT) and indirect fluorescent antibody test (IFAT). Recent molecular biology Viral infections can cause mass mortality, techniques such as PCR, RT–PCR and especially in fry or fingerlings, while older gene probes are becoming popular for the fish may develop resistance or are hardly diagnosis of fish viral infections. 243 Z:\Customer\CABI\A4337 - Woo\A4419 - Woo Vouchers.vp Tuesday, November 05, 2002 11:35:10 AM Color profile: Disabled Composite Default screen 234 G.D. Lio-Po and L.H.S. Lim Channel catfish virus disease (CCVD) and in the spleen. Thereafter, the virus is transported via the blood to the intestine, Channel catfish (lctalurus punctatus) is the liver, heart and brain (Plumb and Gaines, principal host of channel catfish virus 1975). Thus, hyperaemia of the visceral (CCV). Outbreaks occur in most southern cavity, enlarged spleen, and empty stomach states in the USA, while low-grade mortal- and intestine have been observed (Plumb, ity can be induced in blue catfish (Ictalurus 1994). Necrosis of the renal haematopoietic furcatus) and channel catfish × blue catfish tissue and tubules, oedema, necrosis and hybrids by experimental injection