Fish Diseases and Their Control

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Lecture Prepared by:

Prof. G.N.O. Ezeri
Aquaculture and Fisheries Management University of Agriculture, Abeokuta, NIGERIA.


FIS 710 (3 Units) Core Course

• Types of fish diseases, (parasitic, bacterial, fungal, nutritional etc.) • Laboratory methods for fish disease diagnosis, • Prevention, control and therapy of fish disease

• Higher stocking densities call for the introduction of large quantities of concentrated feeds and mineral fertilizers. • This affects the environmental factors in the aquatic environment • environmental changes are stressful and lower body resistance of fish to disease

• Infections and other diseases therefore sets in • Such unfavourable conditions include – crowding, – temperature fluctuations, – inadequate dissolved oxygen, – excessive or rough handling, – sublethal levels of toxic materials.

• Fish diseases are the end result of interactive of the etiologic agent, the susceptible the fish and the environmental condition

Physiological And Biochemical Changes
• These are non-specific physiological and biochemical changes which take place in three phases: – The alarm reaction – The stage of resistance during adaptation to achieve homeostasis under the changed circumstances taking place. – The stage of exhaustion when adaptation has ceased to be adequate and homeostasis is not achieved.

Classification of diseases
• Generally, diseases are classified as
– infections, – parasitic, – non-communicable and – diseases of unknown etiology.

• Infections diseases are caused by viruses, bacteria, fungi and less frequently algae. • Parasitic diseases are caused by protozoa, helminthes and parasitic crustacean. • Non-communicable disease include – nutritional fish diseases (e.g goiter or hyper plasia of the thyroid gland) – diseases associated with physical or physicochemical abnormalities of water e.g gas bubble disease – low temperature disease, water borne irritants

• Diseases of unknown aetiology are diseases for which the causative agents have not been identified. • It includes proliferative kidney disease

• Bacterial diseases are responsible for heavy mortality in both wild and cultured fish. The actual role of these micro-organisms may vary or differ from that of a primary pathogen to that of an opportunist invader of a host rendered moribund by some other disease process.

Microscopic examination
• Can provide information on the size and shape of the bacteria – Rods (1) – Cocci (2) – Spiral (3) • It cannot provide enough information to enable bacteria to be identified

• The taxonomic position of the currently recognized bacterial pathogens of teleosts includes the following families and genera

• The cytophagaceae are single or filamentous rods which are characteristically motile by a sliding movement. • They are gram-ve with orange, yellow or red colonies. • They are usually associated with mucus of normal or diseased fish. • They measure about 0.5um wide by 12um long. • e.g F. columuans, flexibacter (cytophge) Phychrophile • Causes skin infections which may affect lateral line, fin edges, gill lesions,etc

• They are gram-ve non-sporing rods that may be straight or curved, motile by potafeaells, oxidaline chemo-organotroph • They are strict aerobes. • They may produce a fluorescent pigment. • They commonly occur in soil and water. The rods measure about 3um x 0.5um • e.g P. fluorescens. • They with aeromones cause a disease known as Bacterial haemorrhagic septicemia e.g fin-rot,

• This include various genera of small, gram-ve non-sporing rods that germent dexterose to produce acid or acid of gas and one oxidase negative may species are motile by peritrichons flagella. • They measure -0.75um x 2.5um e.g E. tanda which cause conferen of external lesions to the head of affected...
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