LECTURE NOTES ON DISEASES AND PARASITES IN AQUACULTURE

DISEASES AND PARASITES IN AQUACULTURE

Disease is a serious limiting factor in aquaculture, Caused by pathogens, genetic disorders, physical injuries, nutritional imbalances, pollution etc or combinations of these reasons.
Outbreak of diseases in aquaculture occur due to overcrowding, unbalanced nutrition, reduced oxygen content, increase in organic matter, & changes in pH and temperature.
Diseases of fishes can be classified as
        - Communicable  diseases Infectious(caused by microbes) & contageous (caused by           Parasites)
Non- communicable diseases   caused by  Environmental, Nutritional & Genetic factors or unknown factors
Neoplastic  - Tomours  & cancers.
Among these genetic diseases and neo plastic diseases are very rare in Asian countries.
  Viral diseases:-
Viral diseases are limited to young stock & depend on environmental factors and conditions of fish. Cause tissue damage and rapid death of fish.
Once fish is infected, it develops antibodies and protects the fish from second attack. Recovered fish act as carriers of the virus.
Viral diseases are rare in tropical region and seen mostly in temperate regions.
Viral Haemorrhagic Septicaemia is an example.
Infectious pancreatic necrosis, spring viremia of carp, catfish viral disease are other examples.
Iodine treatment, Vitamin administration, exposure to UV and vaccination are some of the treatment measures against viral diseases.
Bacterial Diseases
1. DROPSY(Bacterial Haemorrhagic Septicaemia).
Common bacterial disease, caused by Pseudomonas fluorescens. Symptoms include extreme enlargement of belly due to fluid accumulation, Scale protrusion and inflammation of intestine.
In India it is reported on Clarias batrachus, C.macrocephalus & Osphronemous gourami.
                        
2) TUBERCULOSIS  ( MYCOBACTERIOSIS).
Caused by Mycobacterium marinum( Marineform cause skin lesions in man), M. fortuitum, & M. salmoniphilum.(Fresh Water).
Sympyoms are retarded growth, Extreme emaciation, (weight loss and thinness by loss of sub cutaneous fat), incomplete gonad development & lesions in the internal organs.
3) COTTON WOOL (COLUMNARIS) DISEASE:-
Caused by Flexibacter columnaris. Greyish white spots appear on the body, especially around mouth.
This disease is Common in young fishes.
4) FIN ROT:-
Caused by Aeronomas hydrophila, A. punctuata,  A.pseudomonas fluorescens.  Affecting both young and adult. It appears as a white line on the margin of the fin. Erosion of tissues start at the extremities of fin and progress towards the base  only the fin ray remains in extreme cases.
Fungal Diseases:-
Fungi attack all stages of fish life.
In India fungal diseases are common among carps.
Saprolegnia cause External mycosis in fishes. Here minute, white hair-like out growths appear on the affected parts followed by ulceration.
Branchiomyces cause Gill rot- common in summer, while ponds rich in organic decaying matter.
Protozoan Diseases:-
1)TRYPANOSOMIASIS:-
Caused by Trypanosoma, a flagellate mostly seen in  Carps & Eels, like Clarias batrachus, Heteropneustes fossilis, Wallago attu.
Affected fish lies in a sleeping posture, floating laterally on water surface, breathing slowly and show very little movement.
Disease is transmitted by aquatic leeches.
2)WHITE SPOT DISEASE (ICHTHYOPHTHIRIASIS):-
Caused by Ichthyphthirius multifilis.
Appearance of white small, white specks all over the body and gills. Each spot represent the encysted parasite

DISEASE BY WORMS:-
       Trematodes, Cestodes, Nematodes, leeches.
Larval stages of worms are more injurious. Cause tissue disruption, Metabolic disturbances, poor gonad development., Growth retardation  and lead to death.
Prarasitic infeststion  reduce the market value.
DISEASE BY CRUSTACEANS:-
Argulus or fish louse  have leaf like body. It attaches to the fish and suck blood- wound caused invite secondary bacterial and fungal infection.
Lernaea or Anchor worm- anterior part is modified like an anchor which is buried deep in to the skin of the fish. It feeds on the tissues and erythrocytes, leads to death or secondary infections.
EPIZOOTIC ULERATIVE SYNDROME(EUS)
Most dangerous disease of fresh water fishes of Asian countries.
Apperaed in Thailand in 1980 followed by Philippines and Indonesia. 1990 reached Srilanka.
Appeared in Kerala & Tamil Nadu in 1991. First appeared in Kerala in July- Aug 1991.
The Channa fish in many water bodies of Kerala disappeared due to this disease.
Appear as grey patches on the body surface- becomes red and ulcerated- spreads to internal organs. At later stages fish stop feeding, swims erratically on surface water- wound on body become deeper - succumb to infection.
Gram negative bacteria, Aeromonas and Pseudomonas were believed to cause EUS. Recent sudies prove sapropythic fungus, Aphanomyces as the causative agent.
Deterioration of environmental factors may enhance the disease outbreak. No effective treatment devised.