9 Problems of Fish in Ponds

Fish cultured in ponds can have problems: they can be stressed by a lack of oxygen; they can be eaten by predators; they can be infested by parasites. These problems and some solutions to these problems are discussed in this section.

Diseases

Diseases of pond fish are caused by fungi, bacteria, protozoans, worms, and crustaceans. Usually diseases can be controlled by proper pond management, which includes draining the pond, drying it, and liming it periodically, and also by preventing wild fish or unfiltered water from entering the pond. Some diseases are fatal, but many can be controlled by treating the pond or the fish with chemicals.

Some diseases attack fish in ponds because some other factor is causing stress: overcrowding, low oxygen levels, or not enough food. All of these conditions weaken the fish so they can get diseases more easily. The farmer must watch his fish for signs of stress and disease. Any change in normal behavior may be a sign of disease; for example, gasping at the surface for air, rubbing the body or head against the sides of the pond, or ragged fins and sores on the body. Something is wrong when a fish population stops eating suddenly. So the farmer must check the fish often (see "Management"), especially in very hot weather.

FUNGAL DISEASES These diseases are caused by fungi.

Gill Rot. This is a disease caused by the filamentous fungus, Branchiomyces sanguinis. This disease is first noticed by a red spotting on the gills. Later, the gills become greyish-white and stop working. When the gills stop working, the fish suffocate and die. Gill rot is most common during the hot part of the year and is sometimes associated with large amounts of dung and a "bloom" of plankton.

Treatment: Remove dead fish from the pond; the remaining fish will probably recover. Drain the pond and dry the bottom. Treat the pond with quicklime or copper sulphate to kill the fungus spores. Fill the pond again. Add quicklime every few weeks until there is no more sign of the disease.

Saprolegnia.

This fungus is often associated with Gill Rot. It attacks weakened places (e.g., bruises from handling) on fish. Since it hits already weakened fish, Saprolegnia attacks fish already trying to fight other diseases. Saprolegnia looks like fuzzy, white cotton wool and is often in tufts on the body of the fish. Saprolegnia by itself can kill eggs and fry, but does not kill adult fish. Indian carp are very susceptible to this disease, and common carp eggs are attacked frequently.

Treatment: Use the same treatment as outlined for Gill Rot.

BACTERIAL DISEASES

These are caused by parasites which are actually bacteria.

Furunculosis. This is the most important bacterial disease. This disease causes-ulcers or abcesses in muscle tissue. It then breaks through the skin, and, eventually, becomes a site for fungus infections, like Saprolegnia. This disease attacks in the spring, and is most often found in more temperate species, like trout.

Treatment: Drain the pond and treat it with slaked lime. Disinfect every tool used in the pond (nets, feeding rings, etc.).

Infectious Dropsy. This is caused by the bacterium, Pseudomonas punctata. The symptoms are a swelling of the fishes' belly with water, ulcers on the skin, lengthening of the fins, and deformation of the backbone.

Treatment: Prevent diseased fish from entering the pond. Bury and burn the dead fish.

Columnaris. This is another bacterial disease which causes discoloured patches on the body, loss of scales, and, often, death. This disease can look like a fungal disease, but it is not. If possible, it should be examined under the microscope for positive identification. It is caused by the bacteria Chondrococcus columnaris and Cytophaga columnaris and is often associated with low oxygen levels.

Treatment: Give fish a feed which has terramycin in it. If it is very bad, place each infected fish in a dip (bath) of copper sulfate (2 minutes in a solution of 1 to 2,000) or a dip of malachite green (10 to 30 seconds in a solution of I to 15,000). Treat the pond with 1 ppm of copper sulfate.

PROTOZOAN DISEASES

Ichthyophthirius multifilis. This is the worst protozoan disease. The "ich" disease is caused by a ciliate which forms white spots or pimples on the skin and fins of the fish. Each parasite produces thousands of spores, which can then infect other fish in the pond.

Treatment: Drain the pond, and lime it. Or treat the fish with chemicals as follows:

Formalin 200-250ppm daily bath 15ppm in pond

Malachite green 1.25ppm daily bath/30 minutes 0.5ppm in pond

Methylene blue 2ppm daily bath

Acriflavin 10ppm 3-20 daily baths

Salt 7,000ppm several daily baths

Costia and Trichodina. These are two other ciliate diseases. They are cause by microscopic organisms which attack the skin of fish and cause lesions. Tilapia, the very resistant fish, are attacked by the Trichodina protozoan.

These ciliates cannot be seen by the naked eye, but the lesions and sores that they cause can be seen by looking closely at the fish.

Treatment: Add 3ppm of potassium permanganate to pond. Or dip the fish in baths of 5 to 10% sodium chloride (salt) for 5 to 20 minutes daily for up to one week.

CRUSTACEAN PARASITES

Lernea. The anchor worm is the most common disease of this type (a copepod). This worm attacks the gills or any other part of the body. It burrows into the fish, leaving its two egg cases protruding on the outside of the fish. Lernea causes red sores, and makes the fish thin so that their market value is much lower.

Treatment: Add castor oil in a thin film over the surface of the pond. Treat fish infected with young Lernea in a formalin bath, or remove each parasite by hand.

Arqulus. Argulus is the fish louse. It is a flat, pinkish-red disc that clings to the skin, fins, mouth, or gills. It sucks blood with a piercing organ, which also injects poisons. Young fish may die.

Treatment: Drain and lime the pond. Or place the fish in a bath of 3 to 5% salt, or 250ppm of formalin for 1 hour.

WORM PARASITES

Most of these are external parasites.

Dactylogyrus. This parasite attacks the gills of young fish. The fish are exposed to this worm when they are between 2 and 5cm long.

Treatment: Manage the pond well so that fingerlings grow rapidly past the stage when they are susceptible to Dactylogyrus.

Gyrodactylus. This parasite burrows into the blood vessels of fish through the skin, causing the fish to appear reddish with sores. This worm can cause fish to die from emaciation.

Treatment: Treat ponds with 5 ppm formalin. Treat fish individually in a bath of 25ppm formalin.

Bothriocephalus gowkongensis. This is the tapeworm which often attacks the Chinese carp, especially grass carp. It is difficult to treat this worm; it is found in the fishes intestines.

General Treatments

Farmers often will have trouble finding the proper chemicals for treating their ponds or deciding which disease the fish have and which treatment to give. Here are some general treatments: any of these treatments will help an infected pond.

Baths: Potassium permanganate 4ppm

Salt 3-5%

Copper sulfate 500ppm for 1-2 minutes

Formalin 250ppm for 1 hour

Malachite green 67ppm for 10-30 seconds

Or the farmer can use unslaked lime directly in the pond.

Some pond owners always treat new brood stock with a one-hour bath in 10ppm of potassium permanganate, and then transfer the fish to a bath of 15ppm of formalin for 4 to 12 hours. This ensures that no parasites will be introduced into the pond with the brood stock.

Other Problems

Other problems are caused by deficiency or environmental factors.

Deficiency problems appear because the fish are missing some factor they need to grow and be healthy. The missing factor can be a lack of essential elements like vitamins or minerals. This lack is difficult to detect until a problem exists. So the only way to prevent this kind of deficiency is to be sure the fish are eating the right kinds of food.

Environmental problems are caused by some change in the pond environment which places a stress on the fish, such as a rapid change in water temperature or an increase in pond water acidity. These are not diseases but problems of fish in ponds which can be controlled by watching the water and soil quality of the fish pond, and by preventing any rapid changes from occurring.

Predators

Other problems occur in fish ponds when other animals eat the fish. Frogs, snakes, and birds eat young fish and must be kept out of ponds. The worst predators, of course, are carnivorous fishes, like the Clarias catfishes. Prevent these fish from entering the ponds by screening the water inlet.

In any pond, all unwanted (trash) fish and predators must be removed before stocking the pond. If the pond can be emptied, simply drain the pond, plow and dry the bottom, etc. If the pond cannot be drained, seine the pond as completely as possible. However, many fish escape the net by staying at the edges of the pond. The best way to get rid of the predators is to poison the pond water in a pond which cannot be drained.

USING POISON

The most common poison for use in fish ponds is rotenone. Rotenone can be purchased -- as a liquid or powder -- or it can be gotten from the roots of the derris plant. To make rotenone, collect derris roots and pound them until a milky-white fluid can be squeezed out. This fluid contains rotenone. Apply one kilogram of derris root for every hectare of pond surface area. If using powdered rotenone, use only 0.05 kg/ha. The powder should be dissolved in water and dipped into the pond from buckets.

Other poisons used in fish ponds are quicklime, teaseed cake, camelia seed cake, tobacco waste, and powdered croton seed. These are some application rates:

Quicklime : 160 kg/ha

Teaseed Cake : 150 kg/ha

Camelia Seed Cake : 50 to 200 kg/ha, depending on depth

Powdered Croton

Seed : 50 to 200 kg/ha, depending on depth

Tobacco Waste : 150 to 200 kg/ha

Most of these natural poisons will degrade (break down) and disappear from the water in 7 to 12 days. After this period, seine the pond again. If no live fish are caught, stock the pond.

There are many chemicals which can be used to poison predators in fish ponds. However, many of them stay in the ground too long. Others are dangerous. One of the chemicals which can be used safely is saponin, which is a component of teaseed cake. Apply a dose of 0.5 ppm in the pond.

In most places, there are fishermen and farmers who know of some local plant which causes fish to die. For example, in India large ponds that cannot be drained are poisoned with Mahuca oil cake (Mahuca latifolia, syn. Bassia latifolia), applied at a rate of 150 to 250 ppm (1500 to 2500 kg/ha per meter of water depth). This plant poison breaks down in 10 to 20 days. These types of poison are all better sources of poison than are chemicals. Many times, when there is a tree that overhangs a pond, fish will be killed when the tree leaves drop into the pond. Watch for plants which do this, and use them in ponds instead of poisons in a chemical form.

DO NOT USE CHEMICALS LIKE ENDRIN, DIELDRIN, AND DDT IN PONDS: THEY CAN LAST IN THE GROUND FOR YEARS, AND LATER, KILL ALL THE POND FISH. NEVER USE POISONS WITHOUT FIRST CHECKING WHETHER THEY CAN BE USED IN PONDS. SOME POISONS KILL OTHER ANIMALS AND HUMAN BEINGS, AS WELL AS FISH.

SUMMARY: FISH DISEASES & TREATMENTS

TREATMENT

DISEASE DISEASE ORGANISM IN PONDS IN BATHS

Gill Rot Branchiomyces sanguinis Quicklime Copper Sulfate

Saprolegnia Saprolegnia Quicklime Copper Sulfate

Furunculosis Slaked lime in Drained Pond

Infectious Dropsy Pseudomonas punctata Burn or Bury Dead Fish

Columnaris Chondrococcus columnaris Copper Sulfate 1ppm Copper Sulfate 500ppm

Cytophaga columnaris for 2 minutes

Malachite Green 67ppm for 10-30 seconds

Ich Ichthyophthirius multifilis Formalin 15ppm Formalin 200-250ppm

Malachite Green 0.5ppm Malachite Green 1.25ppm

Methylene Blue 2ppm

Salt 7000ppm

Acriflavin 10ppm

Costiasis and Costia and Trichodina Potassium Permanganate Salt 5-10% for 5-10 Trichodiniasis 3ppm minutes daily

Anchor Worm Lernea Castor Oil Formalin

Fish Louse Argulus Salt 3-5% Formalin 250ppm for 1 hour

Nematodes Dactylogyrus and Gyrodactylus Formalin 5ppm Formalin 25ppm