Overview :
The advent and anticipation of aquaculture is to enhance food production; more income generation and good health for the people. However, like other farming sectors, disease is a substantial source of constraint to aquaculture development and sustainability; from both social and economic points of view .Production costs are increased through investment lost in dead cultured animals, cost of treatment, and decreased quality and quantity of yields. Many diseases are emerging the aquaculture industry is finding it more challenging to guarantee its sustainable development. Disease is a condition in living organisms in which normal physiological functions are being impaired due to alteration in the body systems and typically manifested by distinguishing signs and symptoms (pathological symptoms). Healthy fish have adequate resistance against diseases; they can adapt to reasonable environmental changes and in turn resist diseases.
Nonetheless, diseases occur in fish but before an active fish disease is developed in a culture system pathologically linked factors are involved:
Presence of environmental pathogens
Low resistance of the fish
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Unfavourable water environment. Development of an active disease in fish results from the effect of the association among these (pathologically linked) factors. In a pond, when the pathogen load increases due to external factors (environmental problems such as poor water supply, or other stressors), above what the natural resistance of the fish can cope with, fish become vulnerable to pathogenic infections and diseases. Also, external factors may cause drastic changes in water quality and lower fish resistance. When these happen, fish become susceptible to diseases, even the risks of fish kill is heightened.
Forms of Fish Diseases
There are two broad forms of diseases affecting fish
• Infectious diseases
• Non-infection diseases
Infectious Diseases
Infectious diseases are caused by living factors – pathogenic organisms (viruses, bacteria, fungi or parasites) present in the aquatic environment or carried by other fish, which weaken fish natural resistance (immune system).
Infections can occur internally and externally affecting tissues, organs and other fish body parts. They are mostly contagious diseases and some types of treatments may be necessary to control the disease outbreaks.
Bacterial infections are considered the major cause of mortality in aquaculture . They can infect a single fish and multiply rapidly to cause a substantial fish kill in a few days or weeks. Bacterial diseases are often internal infections and usually require treatment (with antibiotics added to feeds or water). However, bacterial diseases can also be external which may result from rough handling or effects of parasitic infection.
Viral Diseases
Viruses occur in particles and they are obligate pathogens. They depend on the synthesizing structure of the host cells for replication. Viral diseases of fish are difficult to diagnose and control with medications. The best control measure to viral infections is prevention.
Non-Infectious Diseases
Non-infectious diseases (also referred to as systemic diseases) are caused by non-living factors. The diseases are either congenital (such as genetic anomalies or neo plastic conditions) or iatrogenic (induced by external conditions such as environmental or nutritional problems). Non-infectious diseases are not contagious and medications are generally not indicated for them [3]. However, iatrogenic condition can usually be reversed by removing (or adjusting) the cause . Infectious diseases of fish include.
Environmental Diseases
Environmental diseases result from inadequacies in the physical and chemical characteristics of the pond water. They are the most important among the non-infectious diseases in commercial aquaculture. Environmental problems include depletion of dissolved oxygen, extremes in pH, high ammonia, high nitrite, natural or man-made toxins, or mechanical trauma (caused by rough handling, overcrowding, low water levels, or predation). Proper water quality management and handling are necessary in preventing most environmental problems. Prompt disinfection of fish injuries with suitable disinfectants at recommended dosage is encouraged to prevent pathogen infestation.
Nutritional Diseases
Nutritional diseases are the resultant manifestations of excess or deficiency in fish nutritional requirements (carbohydrate, proteins, lipids, mineral salts and vitamins). Most nutritional diseases are difficult to diagnose because of their chronic nature, with the condition only manifesting over a long period of time.
Prevention and Control of Fish Diseases Health management in aquaculture production describes the management practices put in place to prevent and control the occurrence of diseases.
Despite its presence since 2010, little is known of this disease now impacting shrimp farming. Ecological disturbances in particular by GLOBAL WARMING have resulted in the rise of surface water temperatures. In addition, the EUTROPHICATION of many coastal waters is due TO INCREASED SHRIMP FARMING INTENSITY spurred by attractive shrimp prices. These two conditions contributed to the onset of many new viral, bacterial and fungal shrimp diseases.
