Fish Disease Prevention

External Examination of Fish for Possible Diseases

The extension officer is often faced with the problem of on-the-spot examination of fish. In this case, a diagnosis is impossible without laboratory examination. However, external examination of fish samples can be initially done. To do this, note the following physical features of the fish.

• bulging eyes (exopthalmia)
• unusual body color of the fish
• presence of raised scales
• an eroded operculum
• appearance of some hemorrhagic and inflammed areas on the body
• presence of clubbed and/or swollen gills
• swollen body especially at the belly area

Methods of Collecting Fish Samples for Laboratory Examination

When fish samples have to be collected for laboratory examination, observe the following:

• identify fish samples properly as to species, source, type of water and other relevant information
• collect samples from each pond compartment
• select only fish exhibiting sympotoms of a disease
• live samples are preferred at the time of laboratory examination. Samples can be maintained alive by putting them in an oxygenated plastic bag
• if samples cannot be maintained alive, pack them in a plastic bag. Place this bag in another plastic bag with ice around the samples
• examine the samples within six hours after collection. Bring fish samples at the National Freshwater Fishery Center, CLSU Compound, Muñez, Nueva Ecija.

Prophylaxis

Prophylaxis aims to prevent the outbreak of diseases. This can be done through the following methods:

• use screen or saran filters at the outlet of the water supply line to prevent disease-carrying organisms including wild fish from entering the pond or hatchery system
• eradicate wild fishes before stocking as these may be carriers of disease-causing organisms
• Disinfect the nets and/or other paraphernalia with formalin solution especially those used in fish hatcheries
• remove dead fish from the pond. These are excellent hosts of disease-causing organims which multiply quickly
• dry the pond before stocking to kill disease-carrying organisms.

Improvement of the Defense Mechanism of the Fish

• Maintain water quality in ponds. High oxygen and low ammonia content of the water are ideal for maximum growth and good health
• Control stocking. Water quality deteriorates when the stocking density is high in a pond compartment. An over-populated pond also increases metabolic waste build-up and leads to poor utilization of supplemental feeds. Follow the recommended stocking rate in ponds for a particular species.
• Feed the fish properly. A culture system where the fish are kept in artificial confinement, as in "hapa" or aquarium requires complete feed.
• Handle the fish carefully. Handle fish with proper care to avoid breaking the protective mucus coating of the skin which serves as the first line of defense against diseases and external parasites.

Elimination of Environmental Stresses

Fish in intensive culture are continuously affected by environmental changes and by various management practices such as handling, crowding, hauling, dry treatment and (particularly during stocking) unfavorable or fluctuating temperatures of water quality. All these can impose considerable stress on the limited homeostatic mechanism of most fishes. A stress that requires an adjustment exceeding a fish's capability to endure and accommodate is fatal. Less severe stress may also predispose the fish to physiological disorders or to infectious diseases if fish pathogens are present.

Calculation of Treatment Concentration

The basic unit in expressing chemical concentration in treating fish is parts per million (ppm). One ppm is equivalent to one milliliter (ml) of a liquid chemical to be diluted in a cubic meter of water. If the chemical is solid, one ppm is equivalent to one gram of chemical diluted in a cubic meter of water.

The volume of water in a pond may be computed using the following example:

A pond with a dimension of 100 x 100 m and a water depth of 1.0 m is to be treated with 3 ppm of potassium permanganate. What is the quantity of potassium permanganate needed?

Solution:

Water volume = 100 x 10 x 1

Volume = 1,000 m3

3 ppm = 3 g per m3

Therefore:

1,000 m3 x 3 = 3,000 g or 3 kg potassium permanganate

Note: If the chemical in the above problem is liquid such as formalin, then the quantity of chemical needed is 3,000 ml of pure formalin.

Source: http://www.da.gov.ph/tips/tilapia/fingerlings1.html