636.08
Parasitic Diseases of Finfish and Shellfish
By
Dr. Shalini Anand
Preface
Parasites have arisen by evolution from what were free-living animals (animals not living on or in another animal and not reliant on another to draw their nourishment). They often resemble their ancestors a good deal, but have become better adapted for a parasitic life. Some parasites have developed organs, such as suckers for hanging on to their hosts. Many lay tremendous numbers of eggs because the chances that any one egg will infect a new host are incredibly small. Parasites have generally changed biochemically and immunologically, so they can survive inside another organism and not be digester or killed. Some of them depend on their hosts for compounds that their ancestors could synthesize.
Infectious diseases can be divided into acute, subacute, and chronic forms based on the clinical picture. For example, if enteritis of grass carp or black carp occurs in an acute from, it develops rapidly and soon results in a high rate of mortality; it can also quickly disappear. Chronic enteritis, however, kills only a few fish per day but lasts a long time.
Bacteria pathogens of infectious diseases are not strictly parasitic microorganisms. If the conditions for parasitism are unsuitable, saprophytic relationship will develop. Bacteria pathogens have a high adaptability to environmental changes. For example, the enteritis pathogen of grass carp and black carp will be ineffective if the water temperature is below 20°C; however, a water temperature between 20 and 25°C will enhance its virulence. The mail epidemic season runs from late spring to early summer. Zoospores of Saprolegnia become attached to the fish skin and, if the host has been previously injured, the zoospores will grow and multiply, and the fish will become infected.
The shellfish industry, although only a small part of the fish industry as a whole has grown considerably in recent years, and the products are generally high value ones. The principal species in order of importance are Norway lobster or scampi, lobster, scallop, carb, cockle, crawfish and oyster. Mussels and shrimp make only small contributions to British landings at the present time, but their fisheries are capable of considerable expansion. The Norway lobster is landed either whole or headless in ice, and is often frozen in the shell while waiting processing. The meats are extracted from the thawed tails either by hand peeling or by blowing out with air or water jets. The peeled meats are frozen individually, either in an air blast freezer or a liquid nitrogen freezer, glazed and bagged and put into cold storage.
Lobsters are still distributed live inland; the few that are processed are normally cooked and then frozen whole. Carbs, which do not travel well, are processed close to the points of landing. They are boiled whole, and the meats are then extracted from body and claws by hand. The white and brown meats are frozen separately and then wrapped and cold stored. A small amount of crab meat is also canned in Britain, and small amount of cooked whole crabs are distributed chilled to retailers.
Contents
Introduction -
Fish Diseases and Disorders -
Parasites Diseases in Marine Fishes -
Handling Shellfish -
Parasites in Fish -
Diseases and Parasites of Baltic Fish -
Freshwater Fish Parasites -
Pets Control Management and Fish Diseases -
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Prep. /Ayman Ashry
Manage. / Mona Mahmoud
ساحة النقاش