Disease development in fish

Incidence of disease The incidence of disease is due to the breakdown of the delicate balance between host, pathogen and environment(Snieszko in 1970). Irresponsible use of chemical disinfectants and antibiotics is a potential environmental hazard. In fish, stress is usually related to stocking density, environmental quality, handling or transport

Incidence of disease in fish Environ- ment Pathogen Fish

Role of water quality in fish diseases Maintenance of good water quality by making inlet water free from toxic substances and pathogens is one of the integral parts of the health management in aquaculture.

Important steps for low dissolved oxygen Increasing aeration, reduction of feeding rates, control of phytoplankton bloom and water flow management

Water quality criteria for optimum fish health management of warm water and cold water species of fish (mg/l, except pH) Characteristic Cold water Warm water O2 5-Saturation Ph 6.5-8 6.5-9 Ammonia (un-ionised) 0-0.125 0-0.02 Calcium 4-160 10-160 CO2 0-10 0-15 H2S 0-0.002 Iron (total) 0-0.15 0-0.5 Manganese 0-0.01

Contd…. Characteristic Cold water Warm water Nitrate 0-3.0 Phosphorus 0.01-3.0 Zinc 0-0.05 Total Hardness (CaCO3) 10-400 10-200 Total alkalinity (CaCO30 Nitrogen (gas saturation) < 100% <100% Total solids 0-80 1-500

Four major groups of diseases are generally identified in terms of epidemiology Sporadic disease: which occur sporadically in comparatively few members of a population Epizootics: which are large scale out breaks of communicable animal disease occurring temporarily within limited geographical areas Panzootics: which occur in large areas Enzootics: which persist or re-occur as low level out breaks in certain areas.

Three basic types of culture systems Intensive culture system, in which animals are raised in high density, examples are intensively managed tanks and ponds semi intensive systems in which fish or shrimps are raised in moderate densities in ponds , cages or tanks with some management of the system practised

Contd….. extensive systems where they are grown in low intensity ponds or pens in natural bodies of water and where little or no management is practised.

Thanking you