Fish Hatchery Management - fisheries & aquaculture

FISH HATCHERY MANAGEMENlcleanliness. Allshipped-in equipment should be decontaminated thoroughlybefore it is placed in contact with clean hatchery equipment andwater. The liberal use of warm water and soap is recommended. All trucksand equipment should be decontaminated before they enter the hatchery.The drivers and helpers should not be allowed to assist in loading fish. A"KEEP IT CLEAN" motto should be adopted and hatchery staffimpressed with the idea that one slip-up in cleanliness may nullify all previousefforts.Defense Mechanisms of FishesAs with all living organisms, fish stay healthy only if they prevent excessivegrowth of micro-organisms on their external surfaces and invasion oftheir tissues by pathogenic agents. Invasion is inhibited by tissues that providea physical barrier and by natural or acquired internal defense mechanisms.Physical barriers are important, but give variable degrees of protection.Fish eggs are protected by the structurally tough and chemically resistantchorion. However, during oogenesis the egg may become infected or contaminatedwith viruses and bacteria living in the female. Once hatched, thedelicate fry again are vulnerable to invasion.Fishes are protected from injury and invasion of disease agents by theexternal barriers of mucus, scales, and skin. For example, the skin of salmonprotects against fungi by continuously producing and sloughing offinucus, which allows fungi only temporary residence on the host. Mucusalso may contain nonspecific antimicrobial substances, such as lysozyme,specific antibacterial antibodies, and complement-like factors.Gill tissue contains mucus cells that can serve the same purpose as thosein the skin. However, irritants may cause accumulation of mucus on thegill tissue and lead to asphyxiation. This is an example of a defensemechanism that can work against the host.Internal defenses of the fish can be divided into natural nonspecificdefenses and induced defenses. Induced defenses can be either specific ornonspecific. One of the primary natural defense mechanisms is the inflammatoryresponse of the vascular (blood) system. Defense agents in capillaryblood respond to invasion of pathogenic agents and other irritants. Dilationof capillaries increases the supply of humoral and cellular agents atthe focus of infection. The inflammatory response proceeds to dilute, localize,destroy, remove, or replace the agent that stimulated the response.Fish, like most animals, have an important defense mechanism in the formof fixed and wandering phagocytes in the lymphatic and circulatory systems.Phagocytes are cells capable of ingesting bacteria, foreign particles,and other cells. Fish also have natural, noninduced humoral defenses