The chapter deals with the barriers that prevent microbial entry and the various internal defense mechanisms that are part of the host's arsenal in combating in combating invading microbes. It also discusses some of the biological methods of disease prevention and control.

The improvement of existing serological techniques, development of monoclonal antibody technology and the development of new serological approaches are all working together to provide new tools for the detection of disease-causing organisms in fish and crustaceans. Following the introduction of nucleic acid hybridization technique and PCR, it was recognized that the methods offered a sensitive approach to the detection and identification of specific microorganisms as in the case of a bacterial or viral infection in a variety of sample types. Potentially, a characteristic DNA sequence from a single virus particle or cell of a particular organism can be amplified to detectable levels within a short period of time. Conventional diagnostic methods that involve the culture of microorganisms can take days or weeks to complete or very tedious to perform. PCR offers a rapid, very sensitive, very specific and simple alternative. Further developments in immunodiagnostics and emerging technologies such as quantitative PCR, lateral flow assay and loop-mediated isothermal amplification diagnostic tests will revolutionize the detection, identification and quantification of the infectious disease agents. Further, advancements in gene sequencing analyses will enable strain differentiation among closely related viruses.

The chapter provides basic facts about harmful and toxic algae. It also discusses the conditions that stimulate their occurrence, different types of harmful and toxic algal blooms and their effects to fish and marine environment. The different strategies in coping with the problem of harmful and toxic algal blooms are also discussed.

The chapter presents some of the environmental non-infectious diseases of aquatic animals. Non-infectious diseases are caused by adverse environmental conditions, nutritional disorders, or genetic defects. While they can result a sudden mass mortality or death, they are not contagious. Environmental diseases are the most important in aquaculture. This includes low dissolved oxygen, high ammonia, high nitrite, or natural or man-made toxins in the aquatic environment.

Fish and crustaceans that are not weakened by poor environmental conditions, or by other causes, such as parasitic infestation, nutritional deficiency, handling stress, or chemical intoxication, are more resistant to bacterial infections. This is due to the presence of a large amount of bactericidal substances in the blood, which helps overcome infections. So, the best precaution against the occurrence of bacterial infections is to provide the fish with optimum environmental conditions, adequate amounts of the right kinds of food and avoidance of stress, including overcrowding. Vaccination/ immunization and genetic manipulation (i.e., the development of specific pathogen resistant fry) are also some ways of preventing bacterial diseases. The use of antibiotics should always be an option of the last resort.

This chapter deals with parasitic animals of significance to aquaculture because of their harmful effects on fish and crustaceans. It also illustrates the life cycle of major parasites and discusses the various methods in diagnosing diseases caused by parasites, including disease prevention and control.

A textbook on diseases of cultured warmwater fish and shrimps in the Philippines. Eleven chapters cover essential information on the basic principles of disease causation, major diseases of cultured fish and crustaceans, particularly shrimps, and methods of prevention and control. Emphasis is made on major diseases that occur in the Philippines and other countries in the Asian region. Included also are topics on harmful algae, immunology and molecular biological diagnostic techniques.