Asia contributes more than 90 percent of the world aquaculture. production, like other farming system. Aquaculture and fisheries is

Transcription

1 CHAPTER-7 Fish Diseases 7.1. Introduction Asia contributes more than 90 percent of the world aquaculture production, like other farming system. Aquaculture and fisheries is plagued with disease problems resulting from its intensification and commercialization. Parallel conditions occur among infections to different kinds of culture facilities and different regions. These conditions affect host-parasite relationships as well as influencing methods of control or more properly management and they promote the development and execution of involving approaches to solve culture problems involving disease. Fish diseases have been classified according to their cause and general aspects of their etiology, epizootology and epidemiology. The physiological conditions of fish and their entire environment play an important role is connected with the course of diseases. Fish diseases are broadly classified into pathogenic and nonpathogenic diseases. Pathogenic diseases are virus, bacteria, fungi, protozoans, parasitic, crustaceans, helminthes and other parasites, Non-pathogenic diseases are hereditary, ecological, tumors, environmental and vitamin disturbances. The highest important is given to fish diseases which are highly contagious (Pathogenic). The host pathogen relationship generally undergoes several stages of development. The incubation period is when the pathogen multiplies, but the host does not yet show any signs of diseases. The incubation 178

2 period may range from a day or two for virulent pathogens, to prolonged periods of several months. After this asymptomatic period, specific and non-specific signs of disease become evident. Whether the host dies or survive will depend on its ability to resist the infection. During the epidemic, some of the infected fishes may not exhibit clinical signs at all and become carriers capable of transmitting the disease agent or initiating a future epizootic (Pilly, 1992). Disease is now a primary constraint to the culture of many aquatic species, impeding both economic and social development in many areas. This situation can be attributed to a variety of multifaceted and high interconnected factors such as the increased globalization of trade in live aquatic animals and their products; the intensification of aquaculture through the translocation of larvae and broodstock; the development and expansion of the fish trade (Subhasinghe et al., 2001). The increasing of production in culture system causes increases the potential for disease. The fishes are usually more physically and behaviorally stressed they have easier access to infectious agents that have interfered the system and the margin of error for maintaining good water quality is decreased. In each progressive type of system the stocking rate increases and the predicted production rate increases. At each step, new components added to achieve the production increase the risk for acquiring certain infectious and non-infectious conditions. The number and intensity of infectious disease agents occurring in the above types of grow out depend and on a number of factors. These 179

3 factors involve the type of facility, the source of quality of food, water, stock and the group of species of parasites. Some parasites requiring intermediate hosts are most common in a extensive ponds. Undrainable ponds in particular offer hardly scope for change of water, waste removal and aeration, thus gradually reaching a state which may be stressful for fishes. Stressful environment predispose fish to infectious diseases and thus understanding the process involved in fish diseases out breaks in vital for fish health management. In polyculture systems where several species of carps, catfishes and other species are also raised together, artificial feed acceptability is not uniform among all the species drug administration through feed to a particular species is not ensures. India is one of the best producers among the world freshwater fish producers with Indian major carp s viz. catla, rohu, mrigal and pangas is being the most preferred species (FAO, 2003). Pangas is a fast growing fish, which recently become a very popular food fish and valuable species in the South East Asia. In the present observations, major carps along with pangas in the experimental ponds taken for disease observations. Many workers have investigated on the fish diseases for the past decades. Gopalakrishnan (1961) reported that mass mortalities in India in major carp s catla, rohu and mrigala due to motile Aeromonods infections. Snieszko (1974) reported that disease signs caused by Aeromonas, in tropical fish, motile Aeromonas infections manifesting in all these forms have been studied by Gopalakrishnan, 180

4 (1961); Karunasagar et al., (1989); Carnahan, (1993); Joseph and Carnahan, (1994); Karunasagar et al., (1995). Motile Aeromonas are also the most commonly associated bacteria in case of epizootic ulcerative syndromes (Pal and Pradhan, 1990; Torreset et al., 1990; Lio-Po et al., 1991; Karunasagar and Karunasagar, 1994 and Karunasagar et al., 1995). Some of the workers have reported the epizootic ulcerative syndrome (EUS) is fungal associated syndrome with an invasive fungus, Aphonomyces invagis, the predominant species (Roberts et al., 1992, 1993; Willoughby et al., 1995). Further worked on the bacterial diseases of the fish by Leung et al., (1995), (1996); Karunasagar et al., (1995); Henderson et al., (1999); Austin and Austin, (1999). Viral diseases of fishes have been reported by Freiches et al., (1986), (1989); Kasoranchandra et al, (1991); Roberts et al., (1994) and Kanchanakhan, (1997). Fungal diseases are also described by Limsuwan and Chinabut, (1983); Srivastava, (1979); Roberts et al., (1993); Willoughby et al., (1995) and Chinabut et al., (1995). Further various types of diseases were studied by Qureshi et al., (1995); Rottwell et al., (1997); Watson et al., (1998); Bullard et al., (2000); Chang et al., (2002); Freyer and Hedrick, (2003); Wahli, (2005); Ogawa et al., (2006). In order for a disease to spread from either cultured fish to wild fish or vice-versa, certain criteria as reported by Olivier (2002) are essential; presence of pathogen both fish and water sources; presence of susceptible host; viability, in terms of number and longevity of 181

5 pathogen in the environment; viable infection route. However once the pathogen or disease agent is introduced and becomes established into the natural environment, there is little or no possibility for either treatment or eradication. Crustacean parasites are Argulus and Lernea, helminthes parasites are the dangerous parasites in the culture system. Protozoans are also cusses the most significant problems in the culture systems Materials and Methods The fishes were collected from weekly once in the experimental ponds of Devapudi village, Mudenepalli Mondal, Krishna district, Andhra Pradesh, India. The collected fishes were brought to the laboratory, external diseased characters were observed carefully by using magnify lens. Skin scarping and gill rashes observations were done to observe the external signs. The gill lamellae were mounted immediately with glycerin and observe diseased conditions. The skin was carefully observed for identification of ulcers and differentiation is done at the rate of superficial or deep ulcerations. Caudal, pelvic and pectoral fins were observed for colour, deformity and any other necroses. The stomach was observed any abnormal conditions were observed carefully by opening the fish by giving an incision through the vent. The internal organs like spleen, liver, intestine, gallbladder and gonads were carefully observed for any deformities or diseases. The weight of the fish was noted both diseased and normal healthy fish. After observation and identification of the disease, the diseased fish was fixed in 5% formalin and stored 182

6 in laboratory for further study and water quality conditions observed regularly Observations: The infectious fish showed exopthalmic conditions of eyes (Fig. 7.1-A). The eyes are protruded out and external covering of the eye is damaged (Fig. 7.1-B, C). This condition is also known as pop eye in fish. Myxobolus infected fishes were found to be week, lethargic and crowding and they moves near to the water inlet and comes to the surface of the water. Gill filaments were covered with large number of cysts (Fig. 7.2-A, B, C, D and E). Hemorrhage was seen on the body surface as bluish red marks where several necrotic patches and skeletal deformities observed with Bacterial Hemorrhagic septicemia. Further catla, pangas also observed bacterial hemorrhagic septicemia (Fig 7.3 A, B). The skin is lost its original pink coloration, the characteristic features of pathogen and showed pale coloration of gills. The skin is exposed directly due to loss of scales. It showed multiple superficial ulcers. These ulcers at an advanced stage developed into deep scratches. The ulcers are surrounded by a ring of inflammatory necrotizing patricidal hemorrhage exceeds which often seen on the skin (Fig: 7.4-A, B). 183

7 Table: 7.1. Important bacterial diseases reported from Tropical fish Causative Agent Fish affected References Catla, Rohu, Mrigala Gopalakrishan, (1961) Karunasagar et al., (1986, 1989) Aeromonas hydrophila Aeromonas salmonicida Cat fish Djajadiredja et al., (1982) Crucian carp Miyazaki and Kage, (1985) Ornamental fish Hettiarchi and Cheng, (1994) Murrels, barbs, Pearl spot Common carp Tilapia Karunasagar and Karunasagar,(1994) Reddy et al., (1994) Commom carp Bootsma et al., (1977) Citrobacter fruendii Common carp Karunasagar et al.,(1992) Edwardsilella trada Flexibacter columnaris Flexibacter maritimus Flavovacterium spp. Eels Miyazaki and Egusa, (1976) Lia-Po et al., 91982) Seabass Chong and Cho, (1986) Red Sea Bream Wakabayashi et al., (1984) Salmonids Wakabayashi et al., (1980) Mycobacterium spp. Snakehead Adams et al., (1996) Pseudomonas spp. Eels Lia-Po et al., (1982) Staphylococcus aureus Silver fish Shaha and Tyagi, (1986) Seabass Kasorchandra and Boonyaratpalin, (1984) Chang and Chao, (1986) Grouper Chua and Teng, (1987) Vibrio spp. Chong and Chao, (1986) Milkfish Muroga et al., (1986) Snapper Leung et al., (1950) Eles Miyazaki et al., (1977) Rainbow trouts Sharma et al., (1995) Source: Karunasagar et al.,

8 Operculum and jaws are hyperemic, the fish are fins are frayed showing delicate, opaque, pale fin edge (Fig: 7.5-A). The base of the fins is inflamated. Hemorrhages at the base of pectoral, pelvic, dorsal and caudal fins (Fig: 7.5- B, C) are observed with inflammation. Hemorrhages at the base of pectoral fins with ulceration were observed. The gills showed paleness with pectoral hemorrhages. Gill lamellae are frayed and fragmented (Fig: 7.6-A, B, C).The entire brachial apertures are swollen with entire mucous secretions. The stomach is bulged with distended edematous abdomen (Fig: 7.7-A, B, C). Sometimes spine is abnormally curved due to which the fish lost its original shape. Infected fish showed a large polypodial mass in the buccal cavity which interfered and obstruct the respiratory movements due to which fish die of anoxia condition (Fig: 7.8-A). Red mouth disease was also observed in pangas (Fig 7.8 B). The infected fish showed less body weight than the normal in some cases; if the fish was cut ventrally and open for observation of viscera and edematous. Infected fish liver is pale yellowish in color. The stomach is totally destroyed with bacterial capsulation. The gall bladder is blackish colour and become enlarged (Fig 7.11 A). This fish are also showed deformed calcified gonads. Crustacean diseases like Argulus observed in rohu (Fig: 7.9-A, B, C), Lernea infection (Fig: 7.9-D, E) observed in fingerlings of mrigala. Important bacterial disease were reported from tropical fishes are shown in Table

9 7.4. Discussion Diseases of fish are one of the major constraints resulting from intensification of culture and may eventually become a limiting factor to the economics of a successful and sustainable culture. In the present study investigations, Myxobolous were seen in the gills of the mrigala (Fig. 7.2) and in the connective tissue with the ruptured cysts in the secondary lamellae of the gills of the rohu. As the gill lamellar surface was covered by ruptured cyst with necrotic tissues, the normal respiratory functions of the gill appeared to be impaired. Similar conditions observed by several workers. Sanullah and Ahmed (1980) described that the presence of Myxobolous cysts in the different locations of secondary lamellae with hyperplasic gill epithelial cells. Myxobolus infection in common carp is reported to results in lesions, inflammations, congestion and hyperplasia of the gills (Rukyani, 1990). Several damage of to the gills has been observed histological studies during Myxobolous infection of catla, common carp and gible carp (Dykova and Lom, 1988; Wang et al., 2003). Skeletal muscles have been reported to be a location for Myxobolus infection on the fishes is also reported to damage of spleen and gall bladder (Molnar et al., 2002). In the present study enlarged gall bladder observed in catla (Fig 7.11-A). The feeding behavior of the fishes and possibly very close contact of the spores with the fishes appear to be responsible for the infection. Further, these ponds were fertilized with organic manured before stocking of the fishes. Heavy organic loading and different 186

10 anthropogenic activities in the ponds may cause likely to be responsible for these infections (Chavda et al., 2010). Muscles also exhibited the destruction of Myxobolus, necrosis of connective tissues and presence of spores in the infected fishes. Myxozoan infection in gills, muscles and kidney in cyprinids were observed by Longshaw et al., (2005). In muscles spores were seen in the Coelozoic stage. The damage caused to muscle is also seen as necrotic patches and hemorrhages on the body surface. Enlargement of liver, spleen, stomach and gall bladder (Fig: 7.10 A, B) together with loss of cell structure are damage to the fibrilar connective tissue. Further indicates the response of spleen to invading organisms. The spleen is reported to be an integral component of the lymph reticular system playing a crucial role in generating a response to invading pathogens. A severe infection of Myxobolus hypothalamus was reported by Molnar et al., (2006). Myxobolus infection and its effect on catla were studied by Chavda et al., (2010). They concluded that anthropogenic activities in the pond, feeding behavior of the fishes and very close contact of spored with fishes appear to be responsible for Myxobolous infection. Tail rot and fin rot disease is a bacterial diseases of fresh water fish. It is widely distributed in tropical and temperate countries. The disease is characterized by grayish white spots on the body, skin erosion and fin or tail becomes ruptured. Most of the species are susceptible to those diseases and it may cause large mortalities (Frerichs and Roberts, 1989; Noga, 2000). In the present study, the 187

11 infection of tail and fin rot disease was observed in the catla (Fig 7.5- A), rohu (Fig. 7.5-C) and Pangas (Fig 7.4-A). Flavobacterium columnaris is recognised as etiological agent of tail and fin rot disease. It was formerly called Flavobacterium columnaris, but in 1996 it was transferred to the genus Flavobacterium (Decostere et al., 1997). Rahman et al., (2010) worked on the tail rot and fin rot disease occurred in catla (Catla catla) and koi (Anabus testudineus) concluded that the effect of fish shoed lesion and erosion on the tail and fins of fishes. Kubilay et al., (2008) observed and isolated of Flavobacterium columnaris from cultured rainbow trout (Oncorhynchus mysitus) fry in Turkey. Aas et al., (2001) worked in the ulcers and fin erosions of Gadus morhua due to pollution. Prearo et al., (2002) reported typical skin lesion and coetaneous ridding at the base of the fins and abdomen by Vibriosis in cultured brown trout. Stephen Smith (2005) observed localized skin fin lesions along with deep ulcerations and skin cysts. A relationship between fish pathogens or parasites and pollution that fish parasites could be used as environmental factors (Sures, 2004). In the present study revealed that an acute gill erosion with frayed gill lamellae with pale coloration observed in the pangas. Similar observations are followed by Voronin and Chernysheva (1998) observed acute Epitheliocystis infection in the gills of common carp with undifferentiated epithelial cells, chloride and mucous cells with necrotic gill tissue. Xu-Kuidong et al., (2000) observed that Trichodinosis in marine fish for caused serious physiological damage 188

12 of the gills in Lateolabrase japonicus. Epithelial damage of gills with mixed infection was caused by bronchial monogenea in Cachoma fish (Aragort et al., 2005). In the crustacean parasites, Lernea and Argulus causing considerable damage to culture and fishery in the Andhra Pradesh as well as India. Once fishes attached with Lernea are found aberrantly swimming with gliding movement against bottom or submerged substratum with marked emaciation and loss of weight. In severe infection fish appears sick, found floating on the surface of water with belly or abdomen facing up. Argulus are wide spread and harmful ectoparasite on a culture fishes; they damage the directly extracting tissue fluid and haemolymph. Ultimately lesions are formed in the body surface, fins, gills where secondary infection persists. Argulus often cause mortality of fish in culture ponds by puncturing the skin of the host and injecting a cytolytic toxin through their oral string. Further, Argulus signs of extreme irritation on the body, swim at high speed often jump out of the water and rub body surface against submerged objectives. Injuries due to Argulus infection are not only by attachment of parasites on the fish body but extensively by its feeding activities, which involves secretions and injection of digestive fluid and tearing tissue by buccal apparatus and appendages. A circular depression and red coloration on skin epithelium appears is prolonged attachment of parasites. The area of feeding becomes ulcerated and epithelial mucus cells increase in number and copious 189

13 mucus is prolonged. The toxic sections of buccal glands create severe irritation in the skin, scales loosen and ultimately they are lost. The present observations showed a distended edematous with inflamated vent. These results also similar with following observations; the abdominal distention due to liquid presence in the coelom with ulcers and eye loss due to Aeromonas infection in Sea bream (Bovo et al., 1995). Bacterial infection along with external signs of gold fish results abdominal swelling syndrome (Chansue et al., 1999). Acosta et al., (2000) observed that the swollen abdomen in brown trout due to Hofnio alvei infection. Rutilus nautilus heavily infected with Ligula intestinalis showing deformation of abdomen and fin displacement (Loot et al., 2001). Athanassopaulou et al., (2004) reported that the skeletal abnormalities in fish infected with nodovirus. Roberts and Peerson (2005) observed that the abdominal swelling and oedema of ventin Atlantic salmon, Salmo salar with Infectious Pancreatic Necrosis (IPN). In the present study, in pangas swellings on abdomen cause of Abdominal dropsy (Fig 7.7-A) In the present study identified a range of clinical signs of diseases and condition of Pangasius hypophthalmus culture along with major carp s catla, rohu and mrigala. The most prevalent symptom disease ws red spots, anal protrusion, diffused liver, spleen, gall bladder, tail and fin rot, pop eye, abdominal dropsy, gill rot and ulcerations (Fig: 7.7-A, B). Similar type of results was also observed by the following authors (Amin, 2000; Mazid, 2001 Faruk et al., 2004 a, b). 190

14 Fish culture is a significant socio-economic activity, especially rural communities, contribute to livelihood, food security and poverty alleviation through such mechanism as income generation, employment, services, use of local resources, diversified farming practices, domestic and international trade and other economic investment serving the sector (NACA/FAO, 2001; Edwards et al., 2002). Prevalence of fish disease has negative economy impact on fisheries and aquaculture by Worldbank in 1997 was in the range of $US 3 billion per annum (Subasinghe et al., 2001 a, 2001b). Infectious disease are constraining the development and sustainability of the fishes and aquaculture sector through direct production losses and increased operating costs and indirectly, through restriction on trade and impact on biodiversity. In adequate or poorly implemented bio-security measures have led to significant losses due to aquatic animal diseases in many countries around the world. Epizootic ulcerative syndrome is one of the dangerous diseases in culture ponds in costal districts of Andhra Pradesh. The disease occurs more than two decades in South, South-East Asia (Lilley et al., 1992; Roberts et al., 1994 and Das, 1997). In India the first outbreak of EUS occurred in the north-eastern state of Tripura during the monsoon months of September, 1988 following floods from Bangladesh since then it has spread to almost all the other states. By May, 1988, the disease had spread in to the northeastern states of India in channa species and by 1990 out breaks had occurred 191

15 throughout much of the country (Das, 1994). In Kerala also showed that EUS had completely distributed the inland fish market and the economic situation of small scale fishermen and fish vendors. It also affected small scale of aquaculturist. West Bengal also due to EUS, 73 percent of aquaculture operations were adversely affected in the form of mortalities in the ponds. Similar scenarios have been played out in many of the developing countries in South and South East Asia (Lilley et al., 1992; Roberts et al., 1994). In Andhra Pradesh EUS was first reported during October 1990 from Lake Kolleru of West Godavari and Krishna districts of all water areas including irrigation canals, drains, swamps and ponds. The outbreaks usually occurred between Octobers to December, predominantly during the post-monsoon months. The incidence was more in confined water (10-55%) than in river water (4-15%) (ACIAR 1997). Indian major carp rohu, suffer high mortalities as fingerlings (Roberts et al., 1989). In the present study pangas (Fig 7.4 A) also affected Epizootic ulcerative syndrome. Studies on the role of the various groups of pathogens associated with the disease have emphasized particularly the role of Aphanomyces spp. It was shown that a specific slow growing temperature sensitive species. Aphanomyces invaderis is the primary pathogen (Willoughby et al., 1995), later the species name was referred to A. invadans. Aphanomyces invadans is the causative fungus of EUS (Callinan et al., 1997; Lilley et al., 1997). Experimental injection challenges have shown that the pathogenic fungus, A. 192

16 invadans, is capable of causing lesions in rainbow trout at 18 0 C. But is less infective in stickleback, Gasterosteus aculeatus and roach, Rutilus rutilus at C (Khan et al., 1998). Tilapia, Oreochromis niloticus, milkfish (Chanos chanos), chines major carps and European carps are reported to be unaffected by EUS. It hs been shown that fungal growth was suppressed by an intensive inflammatory response in experimentally injected common carp, Cyprinus carpio with zoospores of Aphanomyces from MG and EUS out breaks respectively (Wada et al., 1996; Sharifpour, 1997). Economic losses from diseases are likely to increase as culture expands and intensifies. Assessing the impact of disease in culture systems is not easy, as acute losses are recognised and quantified. Chronic mortalities and poor growth caused by disease are generally not recognised. In order to quantify disease losses, and should be able to indentify disease as the reason for crop loss, slow growth or poor harvest (Mohan and Bhatta, 2002). For sustainable farming, the health management programme should focus on two main approaches like Ecosystem management: environmental management with optimum water, soil quality maintenance, with proper stocking density, devoid of stress to animals and Disease management. The main principles of fish disease control should be based on all-round prophylaxis and prevention is better than treatment approach as the treatment in such systems becomes impractical and uneconomic. 193

17 Disease have been a major constraint to sustainable management practices of the fishery sector, impeding both economic and socio-economic progress in many countries, fish health programme are, therefore, of primary importance for sustainable aquaculture development, production and trade for many countries. The risk of major diseases incursions newly emerging diseases will keep on threatening the sector, and unless appropriate health management measures are maintained and effectively implemented, the government and private sector will be faced with more costs in terms of production losses and the effors needed to contain and eradicate diseases, funds that would have been better spent in preventing their entry into the system. 194