Nov
10
2012

Tilapia Fingerlings 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 to 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

Refer to the tables below for the symptoms and treatment of freshwater diseases, and fresh parasites, signs of infestation and treatment.

Diseases Symptoms Treatment
Ichthyopthirius
  • skin irritation observed in the unusual swimming behavior of the fish

  • white spots of pinhead size surrounding the body and fins

  • sluggish movements, closing of fins

  • apply 15 to 20 ppm of formalin in the pond every other day until the itch disappears

  • apply 1.0 ppm of potassium permanganate in the pond indefinitely

  • apply 2000 ppm of salt in the pond indefinitely

Trichodina
  • appearance of irregular grayish-white patches at the head and back of the fish

  • fins swell and eventually infect their base

  • erratic swimming behavior, rubbing of body against the sides of ponds, cage of tanks

  • apply 2.0 to 5.0 ppm of potassium permanganate in the pond indefinitely

  • apply 15 to 20 ppm of formalin in the pond indefinitely

Costiasis necatrix
  • appearance of bluish-gray patches on the body

  • suffocation due to gill infection

  • appearance of mucus trailing while fish is swimming

  • immerse the fish in a formalin solution with a ratio of 1:4000 (formalin to water) for 30 min

  • dip the fish in a vinegar solution with a ratio of 1:100 (vinegar to water) for five to ten min.

  • immerse the fish in 5% salt solution for 5 to 20 minutes

Skin slime disease
  • bluish-white coloration beginning around the dorsal fin towards posterior

  • suffocation exhibited by rapid breathing

  • fish rub their bodies at the bottom or side of the pond

  • respiratory difficulties due to gill infection

  • peeling off skin and loss of scal

  • apply 25 ppm of formalin in the pond indefinitely

  • immerse the fish in a 20 ppm Lysol solution for 30 min

  • apply 3 ppm methylene blue into the aquarium. This treatment is very expensive for fishponds

  • Immerse the fish in a 1,000 ppm potassium permanganate solution for 30 to 45 min.

Fungal diseases
a. Gill rot disease
b. Branchiomyces sanguinis
  • appearance of white, cottony wool patches in the body

  • appearance of a cottony growth on a single site which starts as bruise

  • the gills stop functioning and the fish dies of suffocation

  • apply 5 percent solution of methylene blue directly to the infected areas of the fish until disease disappears

  • apply crystalline potassium dischronate at the rate of 1 g per 28 liters of water into the pond

  • apply 25 ppm formalin in the pond every other day until the “itch” disappears

Bacterial diseases
a. Tail and fin rot
b. Columnaris
  • appearance of yellow or orange lesions on the head, skin and gills of the fish

  • presence of bluish-gray lesions on the body surface

  • loss of scales

  • apply approximately 10 to 15 ppm of oxytetracycline in the pond

  • immerse the fish in a solution of 20 mL 3 percent hydrogen peroxide per one liter of water for 15 minutes

Freshwater parasites, signs of infestation and their treatment

Diseases Signs of Infections Treatment
Parasitic crustaceans
a. Lernae (anchor worm)
b. Argulus (fish lice)
  • the parasite attacks the gills and other body surface. It encysts the fish skin, leaving its egg cases protruding outside

  • infested fish rubs its body against the pond

  • whitish spots of curled-up worms embedded in the skin of fish

  • the appearance of pinkish-disc attached into the fish skin or the gills

  • apply a flush treatment of 25,000 ppm salt solution for 30 minutes

  • apply 0.25 ppm of Malathion in the pond weekly for five weeks

  • dip the fish in a 0.25 ppm malathion solution for about three to five minutes

  • immerse the fish in a 10 ppm potassium per manganated solution for 30 minutes

  • immerse the fish in a 3.5 percent salt solution

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 symptoms 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 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 organism 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: STII and PCARRD

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