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Color profile: Disabled Composite Default screen 6 Infectious Diseases of Warmwater Fish in Marine and Brackish Waters Leong Tak Seng1 and Angelo Colorni2 1School of Biological Sciences, Universiti Sains Malaysia, Penang, Malaysia; 2Israel Oceanographic and Limnological Research, National Center for Mariculture, PO Box 1212, Eilat 88112, Israel Introduction two main geographic regions, namely West Asia and Southeast Asia. The West Asia The culture of marine finfish in cages that regions present wider fluctuations of envi- hang from floating rafts was successfully ronmental conditions, particularly water initiated in Japan in the 1950s and in South- temperature, whereas in Southeast Asia east Asia in the 1970s. In those early years, they are generally more stable. The species fish for culture were obtained from the of fish cultured in the various regions wild. While in many regions this is still the reflect these environmental differences. way culture is started, some species of fish Other warmwater areas where cage culture are today successfully hatchery-produced. is practised on a commercial scale are the The cage culture system is basically similar tropical islands of the Pacific Ocean. throughout the world wherever intensive The most common species of marine mariculture is practised. However, disease fish cultured in floating cages are summa- types and severity are greatly influenced by rized in Table 6.1. the species of fish, the conditions in which the animals are cultured and the husbandry management. Diseases Caused by Viruses Fish cultured in floating cages become particularly susceptible to disease when Viral diseases in cage-cultured fish have various environmental parameters such as been on the increase since the 1980s in East temperature, salinity, dissolved oxygen and Asia and the 1990s in Southeast Asia (Nakai suspended particles fluctuate suddenly or et al., 1995; Arthur and Ogawa, 1996; widely, or following rough, although often Muroga, 1997; Bondad-Reantaso, 2001; unavoidable, handling operations. Once Roongkamnertwongse et al., 2001; Zhang, conditions suitable for pathological changes 2001). Virological research received a new develop, progress to disease in the warm- impetus following the high mortality in water environment is rapid. Early detection hatchery-bred juvenile fish soon after being of behavioural changes and clinical signs in placed in sea cages (Fukuda et al., 1996; the cultured animals are critical for proper Park and Sohn, 2001). With the increasing diagnosis of the disease. awareness of virus-related diseases and The warmwater culture of marine with new species of fish being selected for finfish in floating cages is concentrated in culture, more reports of known and new ©CAB International 2002. Diseases and Disorders of Finfish in Cage Culture (eds P.T.K. Woo, D.W. Bruno and L.H.S. Lim) 193 203 Z:\Customer\CABI\A4337 - Woo\A4419 - Woo Vouchers.vp Tuesday, November 05, 2002 11:34:54 AM Color profile: Disabled Composite Default screen 194 T.S. Leong and A. Colorni Table 6.1. Species (common name) of marine fish cultured in cages in Asia. Species East Asia Southeast Asia West Asia Serranidae (seabass and groupers) Dicentrarchus labrax (European seabass) − − + Epinephelus aeneus (white grouper) − − + E. coioides (greasy grouper) + + + E. malabaricus (black dot grouper) + + − E. bleekeri (brown grouper) + + − E. fuscoguttatus (tiger grouper) + + − Lutjanidae (snappers) Lutjanus argentimaculatus (mangrove snapper) + + − L. johni (golden snapper) − + − L. russellii (Russell’s snapper) + − − Chanidae (milkfish) Chanos chanos (milkfish) + + − Centropomidae (snooks) Lates calcarifer (Asian seabass) − + − Mugilidae (mullets) Mugil cephalus (mullet) − − + Scorpaenidae (scorpion fishes) Sebastes schlegeli (black rockfish) − − + Carangidae (jacks) Seriola quinqueradiata (yellowtail) + − − S. dumerili (yellowtail) + − − Caranx (Pseudocaranx) dentex (striped jack) + − − Trachurus japonicus (horse mackerel) + − − Tetraodontidae (puffers) Takifugu rubripes (tiger puffer) + − - Sparidae (seabream) Sparus aurata (silver seabream) − − + Rhabdosargus sarba (goldlined seabream) + − − Pagrus major (red seabream) + − − P. schlegeli (black seabream) − − + Acanthopagrus bifasciatusi (black seabream) − − + Sciaenidae (drumfish) Sciaenops ocellatus (red drum) − − + Pleuronectidae (flounders) Paralichthys olivaceus (Japanese flounder) + − - viral diseases are to be expected. The displaying little or no scar tissue (Paperna viruses reported in cultured marine fish et al., 1982). Although the unsightly are summarized in Table 6.2. appearance of the typical lesions renders the infected fish unmarketable, juveniles are considerably more susceptible to the Lymphocystis infection than larger, market-sized stages. Lymphocystis is a highly contagious Host range. Although known to infect 30 infection caused by a cytoplasmic DNA families of marine fish (Wolf, 1988), iridovirus. The disease follows a chronic lymphocystis is a host-specific disease course and, in general, mortalities are (Overstreet and Howse, 1977; Chao, 1984), limited. The infected fish recover within a therefore the disease is most probably few weeks of the onset of the outbreak, caused by a group of different viral strains. 204 Z:\Customer\CABI\A4337 - Woo\A4419 - Woo Vouchers.vp Tuesday, November 05, 2002 11:34:54 AM Color profile: Disabled Composite Default screen Infectious Diseases of Warmwater Fish in Salt Water 195 Table 6.2. Viral diseases of warmwater maricultured finfish. Disease Causative agent Species affected DNA virus Lymphocystis (LCDV) Iridovirus Japanese flounder (Paralichthys olivaceus) Japanese seabass (Lateolabrax japonicus) Seabream (Sparus aurata) Red drum (Sciaenops ocellatus) Red seabream iridoviral RSIV Red seabream (Pagrus major) disease Grouper (Epinephelus malabaricus) RNA virus Viral nervous necrosis Nodavirus Striped jack (Pseudocaranx dentex) (SJNNV and VNN) Black spotted grouper (Epinephelus bleekeri) Greasy grouper (Epinephelus coioides) Black spotted grouper (Epinephelus malabaricus) Grouper (Epinephelus tauvina) Marbled leopard grouper (Plectropomus maculates) European seabass (Dicentrarchus labrax) Asian seabass (Lates calcarifer) In Southeast Asia, only seabass (Lates Diagnosis. The disease is characterized by calcarifer) has been reported to be affected tumour-like masses of tissue on the body by this disease (Limsuwan et al., 1983; Chao, surface (Fig. 6.1). These growths are clusters 1984). In Israel, it was reported in seabream of extremely hypertrophic fibroblastic (Sparus aurata), a species reared in the Red dermal cells (Fig. 6.2). In yellowtail, the Sea but originally imported from the infected cells are dispersed, covered by a Mediterranean Sea (Paperna et al., 1982), layer of epithelium and surrounded by black and in the red drum (Sciaenops ocellatus), pigment cells, thus appearing as small black originally imported from the USA (Colorni dots (Matsusato, 1975). Occasionally inter- and Diamant, 1995). Lymphocystis has nal organs can become infected (Colorni and been listed as a major viral disease Diamant, 1995). of maricultured fish in Japan (Muroga, Lymphocystis-infected cells are mainly 1995). In East Asia, outbreaks of this spherical in shape with a thick elastic mem- disease have been reported for seabass brane, but may be distorted when in clusters, (Lateolabrax japonicus) (Miyazaki and due to pressure from adjacent cells. The Egusa, 1972; Chen, 1996; Park and Sohn, infected cells apparently stimulate prolifera- 1996), yellowtail (Seriola quinqueradiata) tion of the adjacent healthy tissue. After 2 (Matsusato, 1975), Japanese flounder weeks of infection, the cells enlarge signifi- (Paralichthys olivaceus) (Tanaka et al., cantly. Both nucleus and nucleolus present 1984; Park and Sohn, 1996), red seabream large basophilic cytoplasmic inclusion (Pagrus major) (Chen, 1996; Park and Sohn, bodies that react positively for DNA. 1996; Muroga, 1997) and rockfish (Sebastes Diagnosis of lymphocystis disease is schlegeli) (Chun, 1998). Matsuoka (1995) confirmed through histological sections and reported that the incidence of this disease appropriate staining of the tissue lesions. In has increased since the early 1990s, particu- fact, this is one of the few viral diseases that larly in Japanese flounder. can be identified histologically. The obser- vation of the typical icosahedral virions by electron microscopy offers further confirma- Geographic distribution. Lymphocystis tion. Horizontal transmission is the most disease is not restricted to warm seas, but is probable route, facilitated by high stocking widespread throughout the world in both density and unfavourable environmental marine and freshwater fish (Wolf, 1988). conditions. In Southeast Asia, trash fish 205 Z:\Customer\CABI\A4337 - Woo\A4419 - Woo Vouchers.vp Tuesday, November 05, 2002 11:34:55 AM Color profile: Disabled Composite Default screen 196 T.S. Leong and A. Colorni Fig. 6.1. Lymphocystis in Asian seabass, Lates calcarifer. Fig. 6.2. Hypertropic fibroblastic cells in caudal fin of Asian seabass, Lates calcarifer. used as feed may be another source of infec- hexagonal in shape, with a diameter of tion (T.S. Leong, personal observation). 200–240 nm (in red seabream) and 140–160 nm (in brown-spotted grouper) Prevention and control. There is presently (Danayadol et al., 1997; Kasornchandra and no effective therapy for this disease. A Khongpradit, 1997). decrease in stocking density and culling of visibly infected individuals are the only Host range. Red