Preface

'Water' is 'life' and must be protected and conserved. Having its origin in water, life has evolved itself into an enthralling world of coveted and bewilderingly diverse flora and fauna. The dependence of the living world, notably humankind, on the biological wealth of rivers, lakes, seas and oceans, cannot be overemphasized and, possibly, does not need any elucidation. Therefore, there is, perhaps, a requirement to broaden and deepen our comprehension about the aquatic ecosystem with regard to its physical, chemical and biological features and interactions. The water, as an ecosystem, performs a number of significant environmental functions, notably, re-cycling of nutrients, re-charging of ground water, augmentation and maintenance of stream flow and recreation of people, to exemplify a few. Notwithstanding the above, fresh water is one of the most important natural resources crucial for the survival of all living beings. It is even more important for humans as they depend on it also for food production, industrial growth, hydropower generation and waste disposal as well as for cultural requirements. Limnology is the science which deals with the freshwater environments, their physico-chemical characteristics, their biota and the ecosystem processes therein. Limnology is, therefore, universal in its significance. Fishes are significant living components of both lotic and lentic systems. They constitute almost half the total number of vertebrates in the world. Of the c 39,900 vertebrate species known to exist so far in the world, 21,723 are living species of fishes; of which, c 8411 are of freshwater and the rest, 11,650 are marine species. In the Indian region alone, of the c 2500 species, 930 are freshwater inhabitants and 1570 are marine. A living body is prone to suffer from a disease being attacked by pathogen(s) or parasite(s). This is true also with a fish body. Often, a disease may be so virulent, that it could sweep unabated in an epidemic dimension. In this connection, it may be said that, patterns and long-term trends are important when deciding whether or not an epidemic exists in the present period and in predicting future epidemics. Snieszko (1974) had stated that, an overt infectious disease could occur when a susceptible host is exposed to a virulent pathogen under stress. The influence of each sub-set of the environment could be variable; and, disease outbreak (e.g., EUS, in this case) may occur, only if there is sufficient relationship among them. Although a filterable biological infectious agent is thought to be the primary cause of EUS outbreak, it is generally accepted that, certain abiotic factors which result in sub-lethal stress of the fish, are also important in initiation of disease outbreaks. Snieszko cited temperature, eutrophication, sewage, metabolic products of fishes, industrial pollution and pesticides as potential sources of stressful environmental conditions. Life and disease processes of fishes are similar in many ways to those of other vertebrates, in that, most animals have muscles, skeletons, skins and internal organs which function in approximately similar ways. However, there is one major difference: 'fish live in water'. As such, all of their physiological structures and functions are influenced by this fact. Thus, to understand what water means to fish is to lay a foundation for a more complete understanding of what fish need for health and how disease processes are related to physiological and environmental requirements. In order to understand the influence of environmental factors on fish disease, one has to realize that, in aquatic environment, there is a much greater chemical and physical variability than exists in the terrestrial environment. In very large bodies of water, such as oceans, conditions may be relatively stable; but, in the coastal and estuarine areas, there is a greater magnitude of environmental change(s). In small bodies of water, this variability is even greater; while, in fish hatchery operations, many man-made stresses are added. Therefore, in the aquatic environment, life goes on under dynamic and unstable circumstances and fishes must continually adapt to changes in population density pressure, temperature, dissolved gases, light, pH, etc. However, it may be noted here that, the effects of these parameters could be far more severe than those ever faced by the terrestrial animals. Such environmental changes could impose stresses of considerable magnitude on the somewhat limited homeostatic mechanisms of fishes. Epizootic Ulcerative Syndrome or EUS is a hitherto unknown, dreadful, virulent and enigmatic disease among the freshwater fishes which had been sweeping the water bodies in an epidemic dimension almost semi-globally causing large-scale mortality among the freshwater fishes; thus, rendering many of them endangered and throwing the life of the fishermen out of gear through loss of avocation and causing difficulties to the fish eaters through scarcity of fish flesh as a protein-rich source of nutrition. This dreaded fish disease, thus, has been a major concern in several countries of the world, particularly, the Asia-Pacific region. As a historical resume, in Queensland, Australia, an epizootic of marine and estuarine fishes, characterized by shallow hemorrhagic ulcers, had occurred in 1972 with recurrence(s) in subsequent years. The disease had been named as 'red spot disease'. A similar type of disease, characterized by dermal ulcers, had been reported from Papua New Guinea: (a) from the rivers of the south during 1975-76; and, (b) from the north during 1982-88. Concomitantly, Indonesia had also reported similar type of disease in Bogor during 1980, which, subsequently, had spread to West, Central and East Java. This disease was named as infectious dropsy or 'hemorrhagic septicemia'. Later, the disease was reported from Malaysia during 1981-83. The affected fishes had red or necrotic areas of ulceration all over their bodies and were called 'Webak Kudes'. The disease was, subsequently, reported from fishing areas of Kampuchea, during early 1984, along with a significant decrease in the natural fish stock. Also, a similar type of disease had been reported from the southern and central parts of Lao PDR during 1984. Myanmar had experienced the outbreak of EUS during 1984-85 affecting both wild and cultured fish stocks. In Thailand, the disease epizootic was first reported in 1980 in the natural water systems and the disease had recurred somewhat regularly almost every year from 1980 to 1985 in different water bodies. In Sri Lanka, the disease was first reported in 1988 in the Kelani river, Dandugan Oya, and in the nearby streams causing extensive fish mortality. In Bangladesh, the first outbreak of EUS had occurred during February-March 1988 in the rivers Meghna, Padma and Jamuna; as well as, in the adjoining water bodies with colossal loss of the commercial fish stock. After sweeping semi-globally in epidemic dimension, this hitherto unknown enigmatic and virulent fish disease entered India, during July 1988, through Barak valley region of Assam and started causing large-scale mortality among the FW fishes. It had caused panic among the fish consumers and had thrown the life of the poor fishermen out of gear and rendering them starving for days together in view of no sale of fish. And, the author of the present Treatise had decided to start researching on this challenging fish disease problem (sacrificing his remuneration leave, and with the help of many generous souls), as part of discharging his social responsibility, at this crucial juncture of the Society and the People. In India, the outbreak of the virulent EUS fish disease had been first encountered during July, 1988 among the fishes in the Freshwater bodies of North East (NE) India. In 1989, Nepal had also been affected by EUS (Das and Das, 1993; Kar, 2007, 2013). EUS had been a hitherto unknown enigmatic virulent, epidemic among the fishes since about 4 decades. It had been designated by various names, some of which are often colloquial. Egusa and Masuda (1971) had, perhaps, at first, described it in Japan as Aphnomyces infection. The infection had also, possibly, occurred among other fishes, being named as Mycotic Granulomatesis (MG). Such a nomenclature was mainly based on histopathological (HP) results (Miyazaki and Eugusa, 1972). Concomitantly, a hitherto unknown EUS condition had been encountered, since 1972, mainly on the skin of estuarine fishes in Australia. Such an element had been named as Red Spot Disease (RSD) (McKenzie and Hall, 1976). Subsequently, almost similar conditions had occurred among the freshwater fishes throughout South-East (SE) and South Asia since the late 70's. The main symptoms included dermal ulcerations and there had been large scale mortalities among the fishes. The condition was designated as 'Epizootic Ulcerative Syndrome' (EUS) at the consultation of Experts on Ulcerative Fish Diseases held at Bangkok during 1986 (FAO, 1986). In addition to the above, almost similar ulcerative condition had also been reported among the estuarine fishes in the east coast of USA since around 1978. Such a condition was termed as Ulcerative Mycosis (UM) (Noga and Dykstra, 1986). Lack of a comprehensive treatise on 'Epizootic Ulcerative Fish Disease Syndrome' on a global scenario, has prompted this humble piece of work and the author will consider himself amply rewarded if this humble piece of work proves to be useful to those for whom it is meant. Devashish Kar,     Professor, Department of Life Science, School of Life...