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A case study of acute fish diseases in tanks loaded with high levels of organic manures
Aquaculture, 35 (1983) 277-282 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
277
A CASE STUDY OF ACUTE FISH DISEASES IN TANKS LOADED WITH HIGH LEVELS OF ORGANIC MANURES
H.S. TOOR, H.S. SEHGAL and R.S. SEHDEV Fisheries Research Complex, Ludhiana 141 004 (India)
Department
of Zoology, Punjab Agricultural
University,
(Accepted 6 January 1983)
ABSTRACT Toor, H.S., Sehgal, H.S. and Sehdev, R.S., 1983. A case study of acute fish diseases in tanks loaded with high levels of organic manures. Aquaculture, 35: 277-282. Two acute fish diseases, hemorrhagic septicemia, caused by Aeromonas punctata Snieszko and saprolegniasis caused by Saprolegnia pamsitica Coker, were observed in an Indian major carp, Labeo rohita (Ham;). Common carp (Cyprinus carpio Linn.) suffered only from early stages of hemorrhagic septicemia. The diseases were prevalent only in winter and in tanks with a high organic load. INTRODUCTION
Despite recent advances in aquaculture, disease still remains a major concern to the industry. This is due mainly to a rising tendency for intensive culture of aquatic organisms (Sarig, 1976). Apart from mortality, diseases result in significant economic loss by affecting growth, condition factors, fecundity, and many other vital physiological phenomena of fish. Knowledge of the diseases of Indian freshwater fishes is practically lacking, although some preliminary information is available from the studies of Laha et al. (1971) and Pal (1975). EXPERIMENTAL
PLAN AND EPIZOOTIOLOGICAL
DATA
During the winter of 1981, an outbreak of diseases was observed in experimental fish tanks of the Fisheries-Research Complex of Punjab Agricultural University, Ludhiana. The experiments were undertaken to study the role of organic wastes in composite fish culture. Two organic wastes, viz. farmyard manure (FYM) and poultry manure (PM), were tested. In all, 21 concrete tanks each measuring 13.5 X 6 X 1.22 m were used. Water supply to these tanks was from a tubewell. A thin layer of soil was made on the bottoms of all the tanks to hasten the decomposition of organic manures. The water depth was maintained near 1 m. Four different d.oses (8000,16 000,24 000
0044-8486/83/$03.00
o 1983 Elseviea Science Publishers B.V.
and 32 000 kg/ha per year) of air-dried FYM (without washing water) and PM were applied. Half of the total amount of manure(s) was broadcast at the beginning of the experiment and l/llth of the remaining half in each subsequent monthly installment. Each dose was given in five different ways, viz. FYM alone, PM alone, and FYM + PM in 1: 1, 1: 3 and 3 : 1 ratios. This accounted for 20 tanks; the 21st was used as control. Three fish species, Cyprinus carpio (Linn.), Labeo rohita (Ham.) and Cirrhina mrigalu (Ham.), were stocked in the ratio of 2 : 1: 2 at the rate of 12 500 fish/ha. No supplementary feed was given. The diseases occurred only in tanks receiving the highest (32 000 kg/ha per year) and the next highest (24 000 kg/ha per year) treatments, irrespective of the type and/or the combination of the manures. The outbreak was observed on the 149th day of rearing, when C. carpio and L. rohita had attained average weights of 60 g and 150 g, respectively. The total rearing period was 387 days. C. mrigala was not affected. It appears, therefore, that all fish living in a habitat may not be equally affected by a particular disease. Similar observations have been made by Hubbert and Williams (1980) who found that only roach, Rutilus rutilus, were affected with ulcer disease though many more fish (both cyprinids and non-cyprinids) were present in the ecosystem. HEMORRHAGIC
SEPTICEMIA
In early stages of the disease both C. carpio and L. rohita became sluggish and started coming up to the surface. Examination in this stage revealed redness of the lips, barbels, bases of fins and margins of eyes, and scattered red spots on the operculum and dorsal and ventral surfaces of the body. In C. carpio the disease remained restricted to these early stages of hemorrhagic septicemia (HS) and no mortality occurred. In L. rohitu, however, the disease advanced and the red spots on the head, bases of paired fins and dorsal surface of the body developed into dermal lesions leading to the formation of red ulcers with grey margins. This condition was followed by extensive hemorrhagic necrosis (Fig. 1). In this regard, the present study contradicts that of Bauer et al. (1973) who observed that C. carpio is more susceptible to HS than any other species living with it. Estimates showed that 40% (8 out of 20) of L. rohita and 35% (14 out of 40) of C. carpio were affected in tanks receiving 24000 kg/ha per year of organic manures. In tanks receiving 32 000 kg/ha per year, a higher percentage of fish was affected; 85% of L. rohita (17 out of 20) and 65% of C. carpio (26 out of 40). The pathology of the presently observed disease, HS, has variously been assigned to different diseases such as infectious dropsy of carp (IDC; Sch& perclaus, 1930, 1969; Hickling, 1962; Van Duijn, 1967; Buza, 1975), red mouth disease (Sarig, 1976), ulcer disease (UD; Bootsma and Fijan, 1975; Elliot and Shotts, 1980; Hubbert and Williams, 1980) and HS (Bullock and
279
Fig. 1. Cephalic hemorrhagic necrosis in Labeo rohita (Ham.). Fig. 2. Appearance of Saprolegnia parasitica Coker on the necrotic part of the head of Labeo rohita; tufts of cotton-wool-like mycelia are seen. Fig. 3. Caudal fin-rot of Labeo rohita caused by Saprolegniaparasitica.
McLaughlin, 1970; Bauer et al., 1973; Stickney, 1979), thus creating wnfusion. However, the pathologies of carp erythrodermatitis (CE; the subacute or the chronic form of IDC with a bacterial origin) and HS appear to be homologous because red ulcers with grey margins have been shown to be characteristic of CE and not So occur in any other disease (Bauer et al.,
280
1973) whereas they have been regarded as characteristic of only HS by Stickney (1979). The red mouth disease as described by Sarig (1976) also appears to be an early stage of HS. Thus, to avoid confusion, a single term should be used for diseases with the same pathplogical symptoms. In our view HS appears to be a better term as it is more specific and self-explanatory than CE or red mouth (which may reveal the reddening of the skin only) and UD (which merely suggests the formation of ulcers). But detailed studies are required to establish whether these diseases with different names but with similar pathology should be treated as only one disease. The pathogen isolated from the ‘biopsy of dried ulcers of L. rohita (3 specimens) and from the blood culture of both C. carpio and L. rohita (3 specimens each) was characterised as a bacterium, Aeromonas punctutu Snieszko, according to Buxton and Fraser (1977). The baderaemia (HS) was found to be due to this pathogen. The pathogenicity was produced under controlled laboratory conditions ,by artificial inoculation through broth culture, The symptoms of the disease appeared after 10 days at the near limits of the ecological factors observed in the tanks at the time of disease outbreak. The same organism could be reisolated from the experimentally infected fish. The various biochemical tests used to characterize A. punctutu and results obtained are shown in Table I. TABLE I Bacteriological carpio (Linn.)
reactions of Aeromonae
punctata
Sr. no.
Test
Aeromonas
1. 2. 3. 4. 5. 6. 7. 8. 9.
Gram’s stain reaction Morphology Growth at 37°C Motility Indole production H,S production MR test Urease test Breakdown of (i) Glucose (ii) Lactose
-
from Labeo rohitu (Ham.) and Cyprinus
punctata
reactions
Rod + + + + +
+ +
A. punctutu as the cause of CE has also been shown by several other workers (Hickling, 1962; Buza, 1975; Stickney, 1979). However, the reports of Bootsma and Fijan (1975), Elliot and Shotts (1980), and Hubbert and Williams (1980) are contrary and stress that A. sulmonicidu subsp. ucromogenes (Smith) Schubert is the causative organism and A. hydrophilu (Chester) Stainer (= A. punctutu) ads only as a secondary invader. Nevertheless, A.
281
salmonicida subsp. achromogenes has invariably been described as the cause of UD (= HS) in summer months (Bootsma and Fijan, 1975) and also during the breeding season (summer) of the roach Rutilus rutilus (Hubbert and Williams, 1980). However, A. punctata has always been considered as the cause of HS or CE in severe winter months (Hickling, 1962; SchQerclaus, 1969; Stickney, 1979): this was also the case in the present studies. It may be inferred, therefore, that both these species of Aeromonas, i.e. A. punctata and A. salmonicida subsp. achromogenes, may cause the disease HS, but only during the optimal ranges of their respective ecological conditions. Low water temperature and high organic load seem to be involved in causing HS in the present case. Low temperature as the favourable factor for the growth of A. punctata and high incidence of HS has also been stressed by Bauer et al. (1973). Rippey and Cabelli (1980) made similar observations: they recorded higher densities of A. hydrophila (= A. punctatu) in waters with high organic content and in layers of water with a temperature of 16”C, a value near that at which the infection was observed in the present case (17°C). SAPROLEGNIASIS
Soon after their formation (within 20-24 h), the ulcers provided a substratum for the growth of a cotton wool-like fungus (Fig. 2). The isolated fungus from the infected fish was identified as Saprolegnia parasitica Coker on the basis of the structure of antheridia and oogonia, form and size of the zoospores and branching of hyphae. The fungus was not observed to grow on any healthy part of the fish. There occurred an extensive fin-rot (Fig. 3), the fish exhibited abnormal behaviour and succumbed to infection after 2 to 3 days. There is no controversy about the aetiology and/or pathology of the mycosis or the saprolegniasis. Saprolegnia parasitica (one of the causative agents of mycosis, as found also in present investigations) has invariably been accepted as the secondary invader. ACKNOWLEDGEMENTS
The authors wish to thank Dr. D .R. Sharma of the Veterinary Bacteriology and Virology Department, and Dr. B.S. Chauhan of the Plant Pathology Department of Punjab Agricultural University, Ludhiana for the identification of Aeromonas punctata Snieszko and Saprolegina parasitica Coker, respectively .
REFERENCES Bauer, O.N., Musselius, V.A. and Strelkov, Yu.A., 1973. Diseases of Pond Fishes. Israel Program for Scientific Translations, Jerusalem, 220 pp. Bootsma, R. and Fijan, N.N., 1975. Advances in knowledge of viral diseases of fish. In: L.A. Page (Editor), Wild Life Diseases. Plenum, New York, pp. 127-135.
282 Bullock, G.L. and McLaughlin, J.J.A., 1970. Advances in knowledge concerning bacteria pathogenic to fishes (1964-66). In: A Symposium on Diseases of Fishes and Shell Fishes. Special Publ. No. 5, Am. Fish. Sot. Washington, DC, pp. 231-242. Buxton, A. and Fraser, G., 1977. Animal Microbiology. Blackwell, Oxford. Buza, L., 1975. Research into the causative agent, prevention of disease and treatment of infectious dropsy of Cyprinids (IDC). Halhustern Fejl (No. 2), 53 pp. Elliot, D.G. and Shotts, E.B., Jr., 1980. Aetilogy of an ulcerative disease in gold fish Carassius auratus (L.): microbial examination of diseased fish from seven locations. J. Fish Dis., 3 (2): 133-143. Hickling, C.F., 1962. Fish Culture. Faber and Faber Ltd., London, 295 pp. Hubbert, R.M. and Williams, W.P., 1980. Ulcer disease of roach Rutilus rutilus (L.). Bamidgeh, 32 (2): 46-52. Laha, G.C., Mitra, P.M. and Pal, R.N., 1971. A note on the association of parasites of Hilsa ilisha (Ham.) of the Hooghly Estuary. J. Inland Fish. Sot. India, 3: 133-134. Pal, R.N., 1975. Role of fish pathology in aquaculture. J. Inland Fish. Sot. India, 7: 131-136. Rippey, S.R. and Cabelli, V.J., 1980. Occurrence of Aeromonas hydrophila in limnetic environment: relationship of organism to trophic state. Microb. Ecol., 6 (1): 45-54. Sarig, S., 1976. Fish diseases and their control in aquaculture. In: Advances in Aquaculture. FAO Tech. Conf. on Aquaculture, Kyoto, Japan, Fishing News Books Ltd., Farnham, Surrey, England, pp. 190-197. Sctiperclaus, W., 1930. Pseudomonas punctata als Krankheitserreger bei Fischen. Untersuchungen iiber Susswasseraah-otseuche, Leibesholen Wassersucht der Cypriniden, ins besondere des Karpfens, und Fleckenseuche der Weissfiiche. Fischereiforschung, 28: 289-370. Schaperclaus, W., 1969. Virusinfektionen bei Fischen. In: H. Rohrer (Editor), Handbuch der Virusinfektionen bei Tieren. VEB Gustav Fischer, Jena, 52: 1067-1141. Stickney, R.R., 1979. Principles of Warm Water Aquaculture. John Wiley and Sons, NY, Chichester, Brisbane, Toronto, 376 pp. Van Duijn, C., Jnr., 1967. Diseases of Fishes. Iliffe Books, Ltd., London, 309 pp.
277
A CASE STUDY OF ACUTE FISH DISEASES IN TANKS LOADED WITH HIGH LEVELS OF ORGANIC MANURES
H.S. TOOR, H.S. SEHGAL and R.S. SEHDEV Fisheries Research Complex, Ludhiana 141 004 (India)
Department
of Zoology, Punjab Agricultural
University,
(Accepted 6 January 1983)
ABSTRACT Toor, H.S., Sehgal, H.S. and Sehdev, R.S., 1983. A case study of acute fish diseases in tanks loaded with high levels of organic manures. Aquaculture, 35: 277-282. Two acute fish diseases, hemorrhagic septicemia, caused by Aeromonas punctata Snieszko and saprolegniasis caused by Saprolegnia pamsitica Coker, were observed in an Indian major carp, Labeo rohita (Ham;). Common carp (Cyprinus carpio Linn.) suffered only from early stages of hemorrhagic septicemia. The diseases were prevalent only in winter and in tanks with a high organic load. INTRODUCTION
Despite recent advances in aquaculture, disease still remains a major concern to the industry. This is due mainly to a rising tendency for intensive culture of aquatic organisms (Sarig, 1976). Apart from mortality, diseases result in significant economic loss by affecting growth, condition factors, fecundity, and many other vital physiological phenomena of fish. Knowledge of the diseases of Indian freshwater fishes is practically lacking, although some preliminary information is available from the studies of Laha et al. (1971) and Pal (1975). EXPERIMENTAL
PLAN AND EPIZOOTIOLOGICAL
DATA
During the winter of 1981, an outbreak of diseases was observed in experimental fish tanks of the Fisheries-Research Complex of Punjab Agricultural University, Ludhiana. The experiments were undertaken to study the role of organic wastes in composite fish culture. Two organic wastes, viz. farmyard manure (FYM) and poultry manure (PM), were tested. In all, 21 concrete tanks each measuring 13.5 X 6 X 1.22 m were used. Water supply to these tanks was from a tubewell. A thin layer of soil was made on the bottoms of all the tanks to hasten the decomposition of organic manures. The water depth was maintained near 1 m. Four different d.oses (8000,16 000,24 000
0044-8486/83/$03.00
o 1983 Elseviea Science Publishers B.V.
and 32 000 kg/ha per year) of air-dried FYM (without washing water) and PM were applied. Half of the total amount of manure(s) was broadcast at the beginning of the experiment and l/llth of the remaining half in each subsequent monthly installment. Each dose was given in five different ways, viz. FYM alone, PM alone, and FYM + PM in 1: 1, 1: 3 and 3 : 1 ratios. This accounted for 20 tanks; the 21st was used as control. Three fish species, Cyprinus carpio (Linn.), Labeo rohita (Ham.) and Cirrhina mrigalu (Ham.), were stocked in the ratio of 2 : 1: 2 at the rate of 12 500 fish/ha. No supplementary feed was given. The diseases occurred only in tanks receiving the highest (32 000 kg/ha per year) and the next highest (24 000 kg/ha per year) treatments, irrespective of the type and/or the combination of the manures. The outbreak was observed on the 149th day of rearing, when C. carpio and L. rohita had attained average weights of 60 g and 150 g, respectively. The total rearing period was 387 days. C. mrigala was not affected. It appears, therefore, that all fish living in a habitat may not be equally affected by a particular disease. Similar observations have been made by Hubbert and Williams (1980) who found that only roach, Rutilus rutilus, were affected with ulcer disease though many more fish (both cyprinids and non-cyprinids) were present in the ecosystem. HEMORRHAGIC
SEPTICEMIA
In early stages of the disease both C. carpio and L. rohita became sluggish and started coming up to the surface. Examination in this stage revealed redness of the lips, barbels, bases of fins and margins of eyes, and scattered red spots on the operculum and dorsal and ventral surfaces of the body. In C. carpio the disease remained restricted to these early stages of hemorrhagic septicemia (HS) and no mortality occurred. In L. rohitu, however, the disease advanced and the red spots on the head, bases of paired fins and dorsal surface of the body developed into dermal lesions leading to the formation of red ulcers with grey margins. This condition was followed by extensive hemorrhagic necrosis (Fig. 1). In this regard, the present study contradicts that of Bauer et al. (1973) who observed that C. carpio is more susceptible to HS than any other species living with it. Estimates showed that 40% (8 out of 20) of L. rohita and 35% (14 out of 40) of C. carpio were affected in tanks receiving 24000 kg/ha per year of organic manures. In tanks receiving 32 000 kg/ha per year, a higher percentage of fish was affected; 85% of L. rohita (17 out of 20) and 65% of C. carpio (26 out of 40). The pathology of the presently observed disease, HS, has variously been assigned to different diseases such as infectious dropsy of carp (IDC; Sch& perclaus, 1930, 1969; Hickling, 1962; Van Duijn, 1967; Buza, 1975), red mouth disease (Sarig, 1976), ulcer disease (UD; Bootsma and Fijan, 1975; Elliot and Shotts, 1980; Hubbert and Williams, 1980) and HS (Bullock and
279
Fig. 1. Cephalic hemorrhagic necrosis in Labeo rohita (Ham.). Fig. 2. Appearance of Saprolegnia parasitica Coker on the necrotic part of the head of Labeo rohita; tufts of cotton-wool-like mycelia are seen. Fig. 3. Caudal fin-rot of Labeo rohita caused by Saprolegniaparasitica.
McLaughlin, 1970; Bauer et al., 1973; Stickney, 1979), thus creating wnfusion. However, the pathologies of carp erythrodermatitis (CE; the subacute or the chronic form of IDC with a bacterial origin) and HS appear to be homologous because red ulcers with grey margins have been shown to be characteristic of CE and not So occur in any other disease (Bauer et al.,
280
1973) whereas they have been regarded as characteristic of only HS by Stickney (1979). The red mouth disease as described by Sarig (1976) also appears to be an early stage of HS. Thus, to avoid confusion, a single term should be used for diseases with the same pathplogical symptoms. In our view HS appears to be a better term as it is more specific and self-explanatory than CE or red mouth (which may reveal the reddening of the skin only) and UD (which merely suggests the formation of ulcers). But detailed studies are required to establish whether these diseases with different names but with similar pathology should be treated as only one disease. The pathogen isolated from the ‘biopsy of dried ulcers of L. rohita (3 specimens) and from the blood culture of both C. carpio and L. rohita (3 specimens each) was characterised as a bacterium, Aeromonas punctutu Snieszko, according to Buxton and Fraser (1977). The baderaemia (HS) was found to be due to this pathogen. The pathogenicity was produced under controlled laboratory conditions ,by artificial inoculation through broth culture, The symptoms of the disease appeared after 10 days at the near limits of the ecological factors observed in the tanks at the time of disease outbreak. The same organism could be reisolated from the experimentally infected fish. The various biochemical tests used to characterize A. punctutu and results obtained are shown in Table I. TABLE I Bacteriological carpio (Linn.)
reactions of Aeromonae
punctata
Sr. no.
Test
Aeromonas
1. 2. 3. 4. 5. 6. 7. 8. 9.
Gram’s stain reaction Morphology Growth at 37°C Motility Indole production H,S production MR test Urease test Breakdown of (i) Glucose (ii) Lactose
-
from Labeo rohitu (Ham.) and Cyprinus
punctata
reactions
Rod + + + + +
+ +
A. punctutu as the cause of CE has also been shown by several other workers (Hickling, 1962; Buza, 1975; Stickney, 1979). However, the reports of Bootsma and Fijan (1975), Elliot and Shotts (1980), and Hubbert and Williams (1980) are contrary and stress that A. sulmonicidu subsp. ucromogenes (Smith) Schubert is the causative organism and A. hydrophilu (Chester) Stainer (= A. punctutu) ads only as a secondary invader. Nevertheless, A.
281
salmonicida subsp. achromogenes has invariably been described as the cause of UD (= HS) in summer months (Bootsma and Fijan, 1975) and also during the breeding season (summer) of the roach Rutilus rutilus (Hubbert and Williams, 1980). However, A. punctata has always been considered as the cause of HS or CE in severe winter months (Hickling, 1962; SchQerclaus, 1969; Stickney, 1979): this was also the case in the present studies. It may be inferred, therefore, that both these species of Aeromonas, i.e. A. punctata and A. salmonicida subsp. achromogenes, may cause the disease HS, but only during the optimal ranges of their respective ecological conditions. Low water temperature and high organic load seem to be involved in causing HS in the present case. Low temperature as the favourable factor for the growth of A. punctata and high incidence of HS has also been stressed by Bauer et al. (1973). Rippey and Cabelli (1980) made similar observations: they recorded higher densities of A. hydrophila (= A. punctatu) in waters with high organic content and in layers of water with a temperature of 16”C, a value near that at which the infection was observed in the present case (17°C). SAPROLEGNIASIS
Soon after their formation (within 20-24 h), the ulcers provided a substratum for the growth of a cotton wool-like fungus (Fig. 2). The isolated fungus from the infected fish was identified as Saprolegnia parasitica Coker on the basis of the structure of antheridia and oogonia, form and size of the zoospores and branching of hyphae. The fungus was not observed to grow on any healthy part of the fish. There occurred an extensive fin-rot (Fig. 3), the fish exhibited abnormal behaviour and succumbed to infection after 2 to 3 days. There is no controversy about the aetiology and/or pathology of the mycosis or the saprolegniasis. Saprolegnia parasitica (one of the causative agents of mycosis, as found also in present investigations) has invariably been accepted as the secondary invader. ACKNOWLEDGEMENTS
The authors wish to thank Dr. D .R. Sharma of the Veterinary Bacteriology and Virology Department, and Dr. B.S. Chauhan of the Plant Pathology Department of Punjab Agricultural University, Ludhiana for the identification of Aeromonas punctata Snieszko and Saprolegina parasitica Coker, respectively .
REFERENCES Bauer, O.N., Musselius, V.A. and Strelkov, Yu.A., 1973. Diseases of Pond Fishes. Israel Program for Scientific Translations, Jerusalem, 220 pp. Bootsma, R. and Fijan, N.N., 1975. Advances in knowledge of viral diseases of fish. In: L.A. Page (Editor), Wild Life Diseases. Plenum, New York, pp. 127-135.
282 Bullock, G.L. and McLaughlin, J.J.A., 1970. Advances in knowledge concerning bacteria pathogenic to fishes (1964-66). In: A Symposium on Diseases of Fishes and Shell Fishes. Special Publ. No. 5, Am. Fish. Sot. Washington, DC, pp. 231-242. Buxton, A. and Fraser, G., 1977. Animal Microbiology. Blackwell, Oxford. Buza, L., 1975. Research into the causative agent, prevention of disease and treatment of infectious dropsy of Cyprinids (IDC). Halhustern Fejl (No. 2), 53 pp. Elliot, D.G. and Shotts, E.B., Jr., 1980. Aetilogy of an ulcerative disease in gold fish Carassius auratus (L.): microbial examination of diseased fish from seven locations. J. Fish Dis., 3 (2): 133-143. Hickling, C.F., 1962. Fish Culture. Faber and Faber Ltd., London, 295 pp. Hubbert, R.M. and Williams, W.P., 1980. Ulcer disease of roach Rutilus rutilus (L.). Bamidgeh, 32 (2): 46-52. Laha, G.C., Mitra, P.M. and Pal, R.N., 1971. A note on the association of parasites of Hilsa ilisha (Ham.) of the Hooghly Estuary. J. Inland Fish. Sot. India, 3: 133-134. Pal, R.N., 1975. Role of fish pathology in aquaculture. J. Inland Fish. Sot. India, 7: 131-136. Rippey, S.R. and Cabelli, V.J., 1980. Occurrence of Aeromonas hydrophila in limnetic environment: relationship of organism to trophic state. Microb. Ecol., 6 (1): 45-54. Sarig, S., 1976. Fish diseases and their control in aquaculture. In: Advances in Aquaculture. FAO Tech. Conf. on Aquaculture, Kyoto, Japan, Fishing News Books Ltd., Farnham, Surrey, England, pp. 190-197. Sctiperclaus, W., 1930. Pseudomonas punctata als Krankheitserreger bei Fischen. Untersuchungen iiber Susswasseraah-otseuche, Leibesholen Wassersucht der Cypriniden, ins besondere des Karpfens, und Fleckenseuche der Weissfiiche. Fischereiforschung, 28: 289-370. Schaperclaus, W., 1969. Virusinfektionen bei Fischen. In: H. Rohrer (Editor), Handbuch der Virusinfektionen bei Tieren. VEB Gustav Fischer, Jena, 52: 1067-1141. Stickney, R.R., 1979. Principles of Warm Water Aquaculture. John Wiley and Sons, NY, Chichester, Brisbane, Toronto, 376 pp. Van Duijn, C., Jnr., 1967. Diseases of Fishes. Iliffe Books, Ltd., London, 309 pp.