Fish: Diseases and Pests
Booklet No. 535
Fisheries and Aquaculture: FACS - 3
II. Diseases of Fish
III. Pests of Fish
Like all other organisms, fish also get sick and is affected by various kinds of diseases and pests, especially in the intensive and commercial fish culture, resulting in huge loss to the farmers. Some of the diseases are epidemic and contagious and therefore, special precautions are needed to prevent them. Therefore, some basic theoretical knowledge about the common diseases and their management practices is essential for the growers to take precautions as well as to treat the diseases. This knowledge is especially needed for the common people and the social workers who are promoting fish farming as an income generating programme among the people.
Dr. K.T. Chandy, Agricultural & Environmental Education
Fishes are infected by many disease causing organisms such as virus, bacteria, fungi, protozoa, nematodes, and internal parasites like tape worms, crustaceans etc. Besides these, there are problems caused by harmful insects, voracious fishes, amphibians, reptiles, birds and mammals. I have tried to enumerate the different organisms causing diseases to the fishes, just to give an idea of the various sources and causes of diseases. Each disease is very complicated and different from the other. Therefore, dealing with fish diseases is not as simple as people usually think.
The fish farmers are usually poor and illiterate, so they are unable to understand that there are millions of micro- organisms which cause various diseases to the fishes, because they cannot see these micro-organisms. However, there is a need to educate them in these complicated matters. It is not only the fish farmers but also all the social workers who are working among the poor farming people, need to be educated in the basics of fish farming and fish diseases. Quite often they prepare a project on fish farming for the people without knowing anything about the fish farming and finally end up in utter failure with bitter experience.
It is not possible to describe all the diseases that occur to the fishes as there are too many in number. Only the most common diseases, that are affecting the Indian and Chinese carps, a few diseases affecting the eels and catfishes are de- scribed here. It must be clear to the reader that an ordinary illiterate person normally cannot identify all the diseases of human beings and animals however much he tries to educate himself on those diseases so also a fish farmer will be seldom able to identify correctly each disease. This booklet never intends to make anyone a specialist in fish diseases, but it is meant to introduce a common man into the whole world of fish diseases:
II. Diseases of Fish
As already mentioned, diseases of fishes are caused by various types of micro-organisms like virus, bacteria, fungi, protozoa, etc. Hence, the best way to study them is to study under the classification of causal organisms.
A. Viral diseases
Virus is considered to be the lowest form of life and the link between the living and non-living. Some of the important viral diseases of fish are briefly described here.
1. Spring viremia of carp (SVC)
Spring viremia of carp is also known as infectious dropsy of carp (IDC). This is caused by a virus belonging to the Rhabdovirus group with ribonucleic acid (RNA) structure and is called Rhabdovirus caprio. It occurs in the spring when the water temperature is raising (13 to 200 C) but it occurs most commonly when the temperature of the water is 170 centi- grade. It is noticed that the outbreak ceases when the temperature exceeds 200 centigrade. This disease usually occur in fish which are to one year old. It spreads fast and the mortality ranges between 80 to 90 % in, 2 to 3 weeks time.
This disease is common among the carp in Europe and fortunately, it is not yet reported in our country. Because the virus cannot survive in temperatures above 20oC and our country mostly falls within the tropical and subtropical climates. The affected fish show darkening of their body, and then tend to assemble at the water inlet. They exhibit sluggish breathing and finally tilt to one side. In the advanced stage of disease, symptoms like abdominal distension, protrusion of the eyes, reddening and swelling of the anus, anaemia and haemorrhagic spots in the gills are seen. Various internal organs like intestine, spleen, kidney, etc, show swelling and degradation.
Scientists are of opinion that IDC is often mixed with bacterial disorders. However use of antibiotics like chloramphenicol, streptomycin and oxytetracycline in the fish breeding ponds is found to be effective. The antibiotics are better, if given through the artificial feed or through a bath or through injection. The dosage depends on the strength of the medicine and as per manufacturers instruction. The farmer should seek the help of specialists on fish diseases.
2. Swim bladder inflammation (SBI)
It is caused by SBI virus belonging to the Rhabdovirus group with Deoxy ribo Nucleic Acid (DNA) chromosome structure. This is also a common disease in the Europe. Usually, young fishes up to two months are infected more and the mortality could reach 100 per cent. In the grown up fishes the incidence of this sickness is rare. Unlike the SVC/ IDC this disease occur at medium temperatures. The suitable temperature range for the replication SBI virus is found to be between 15 –28o C and no growth takes-place above 33°C and below 5° Centigrade.
In the initial stages the inflammation occurs in the wall tissue of the swim bladder, especially at the bottom of the swim bladder walls. Gradually, bleeding spots appear and brown or black spots appear leading to necrosis and the swim ' bladder is destroyed. By this time the infection would have extended to the other internal organs also.
Administration of antibiotics either by injection or orally through feed is found to be effective to control this disease. A dose of 40 mg of chloramphenicol per kilogram weight of the fish either as abdominal injection or orally through feed is found to be effective. In the case of yearlings 3 -4 administrations lasting for 10 days, and at 5-8 day intervals 20 -30 mg of methylene blue per individual is reported to be useful. For two-year old fish 2-4 administrations of 35-40 mg and for adult fish administration of food for 3 days in which 3 gm per kg of dry feed followed by feed without drug and the cycle being repeated three times.
3. Viral renal disease of eels
The virus is identified as EV-E virus but to which group it belongs is not yet confirmed. This disease is particularly affecting the eels. It causes inflammation mainly on the gills and kidneys and hence is called "gill kidney in11ammation". Eventually the inflammation leads to necrosis and degeneration of these organs and death of the eels.
Fortunately, so far this disease is not yet reported in our country. Providing antibiotics through the feed as mentioned in the previous diseases described is probably the best way to control this disease.
4. Channel catfish viral disease
This disease is mainly affects the catfish and hence it is called catfish virus belonging to Herpes virus which has the DNA structure of chromosomes. It usually affects the finger- lings of less than four months old during the period between June to September when the temperature exceeds 230 centigrade.
The affected fish exhibit abnormal swimming patterns, circling on their sides, exhibiting convulsions, sinking to the bottom of the pond and finally floating on the surface of the water and die. They exhibit abnormal distension and protrusion of the anus in the terminal stages. The disease is also characterized by the protrusion of eyes and extreme fading of gills.
Treatment with antibiotics as mentioned in the previous diseases is found to be effective besides the prophylactic measures like cleanliness and proper maintenance of the pond.
5. Pox disease of carps
The virus causing the pox disease is identified as Carp pox virus belonging to a group of virus called DNA Herpes- virus. This is also called papilloma disease since it is characterized by the dense formation of papilloma in various sites on the trunk, head, and fins of carp fish. The papilloma are white or pink in colour.
The disease does not seem to be fatal however, it affects the growth and development of the fish. The virus is not yet isolated and hence its preventive and curative measures are not finalized. However, administration of antibiotics already mentioned through feed is found to be effective.
6. Lymphocystis disease
It is fairly certain that Lymphocystis is caused by virus. Though it is commonly occurring in the wild fish the cultivated fishes are also affected by it. However it is not reported to be really fatal.
Small blister-like swellings appear scatteringly or in clusters on the surface of the trunk, head, fins and other parts of the body. The disease occur in high temperatures (summer months) and automatically disappear when the temperature becomes less.
Antibiotics may be used at the beginning of the infection. However, proper sanitation and other prophylactic measures are necessary to control the incidence of the disease.
Proper feeding through the natural and artificial feeds is also a necessary element in the prevention and control of this disease.
B. Bacterial diseases
There are a number of bacterial diseases occurring among the cultivated fish. The common ones occurring in India are briefly described here.
1. Tail and fin rot
As the name indicates this disease is characterized by the white margins on the fins and putrefaction of the fins and tails. All the Indian major carps such as catla, rohu and mrigal are susceptible to this disease. It is caused by the bacteria called Myxobacters and Aeromonas sp.
This disease occurs mostly among the young ones during summer months. Besides the high temperature high organic material settled at the bottom of the pond is also a predisposing condition for the outbreak of this disease.
As curative measure feed the fishes with a feed mixed with either the antibiotic terramycin or sulphadiazine at the rate of 100 mg per kg of feed. The fishes are also given common salt bath or formalin bath in 3% salt solution. Dipping in a solution of 250 ppm potassium permanganate for , two minutes is also found to be effective.
2. Eye disease
This disease is more common among the catla fish. The eyes look reddish the lens become cloudy affecting the movement and feeding. Eventually the fish become weak and die resulting in poor production.
The treatment for this disease is the same as those pre-scribed for the previous bacterial disease namely the salt water bath, antibiotics and dip in a solution of potassium permanganate.
3. Dropsy disease
Dropsy disease is characterized by the accumulation of water in the body cavity or scale pockets. It is mainly because of the dysfunction of the kidney. Excessive accumulation of the organic matter is considered to be one of the factors causing the occurrence of this disease. It is caused by the bactcria called Aeromonas species. This disease is common during the summer months.
The treatments are the same as those prescribed for the above bacterial diseases. General sanitation and removal of excessively accumulated organic matter are additional help in controlling this disease.
The ulcers commonly occur among the Indian carps catla, rohu and rnrigal during the summer months and it is caused by some unidentified bacteria, Ulcers are formed on the body of the fishes. These ulcers vary in sizes from pimple like structures. to very conspicuous sores.
Besides contamination from other affected fishes excessive accumulation of putrefied organic matter at the bottom of the ponds and canals is a favourable Condition for the incidence of this disease.
Besides general sanitation and removal of excessive organic matter treatments prescribed for the other bacterial diseases are administered for this disease also. However, treatments should be done at the beginning of the incidence of the disease.
5. Columnaris disease or reddish blotches
Columnaris disease is characterized by the reddish bruises, oozing of blood and formation of clots at the posterior part of the fish. Though all the members of the carp family are affected by this disease silver carp, rohu and catla are found to be more susceptible. The causal organism is still to be identified and named.
Unlike other bacterial diseases described so far this disease occur mostly in the post winter months. Besides excessive accumulation of the decomposed organic matter higher stocking density is also a reason for the incidence of this disease.
The treatments are same as those prescribed for the other bacterial diseases besides the general sanitation and prevention of excessive accumulation of the organic matter.
C. Fungal diseases
These diseases are caused by various organisms belonging to fungi family. There are many fungal diseases affecting the fishes in the commercial culture. Only the important and more relevant ones are discussed here.
This is also known as "water mold disease" or "aquatic fungus disease". This is caused by a group of fungi belonging to Saprolegnia mold. The hyphae of the mold grow extensively giving the appearance of cotton like growth on the outer tissue of the body of the fish and can be clearly seen by any body. Several species of this fungus are known to cause the disease showing the main symptom of cotton like structures.
Almost all the species of fishes are affected by this disease. High amount of decaying organic matter settled at the bottom of the pond is an addition cause for the incidence of this disease. A bath of 5% solution of common salt is found to be eftectivein controlling this disease. By treating the pond with Malachite green at the rate of 0.1 gm per litre of water is another method of controlling the disease. A bath of 0.5 gm of copper sulphate per litre of water or one gm of potassium permaganate per litre of water is another alternative to the bath at common salt.
Branchiomyces is also called gill rot from the symptom seen in the fishes. Almost all the species are affected by this disease. The blood vessels are blocked due to the disease, leading to the death of the fishes. It is caused by the fungus called Branchimyces. Accumulation of highly decayed organic matter at the bottom of the pond is also said to be the,.
reason for the incidence of this disease.
Addition of lime at the rate of 150 kg per ha and bath to the infected fishes in 3-5 % solution of sodium chloride for 3-4 minutes are also found to be effective in controlling this disease.
D. protozoan diseases
Protozoa are microscopic and unicellular organisms found every where. Some of these are pathogenic and some are nonpathogemc.. Numerous protozoan parasites live on the bodies of the fish causing various types of diseases. They attack the skin both on the surface and underneath, the gills and later on spread to the other organs. Some of the common protozoan diseases are described here.
1. Gill spot disease
Gill spot disease usually occur during the post monsoon and winter months. The young ones 'of catla fish are more susceptible to this disease. The exact causal organism is called Thelohane/lus catlae.
The affected fishes are seen with white cysts slowly spreading over to the gills and other parts of the body. The growth is retarded. Excessive mucus secretion from gills and irregular growth of gills epithilium are also observed.
Higher rate of stocking, general weakness due to loss of appetite or lack of feed availability in winter and .he presence of the spores of the causal organisms in the pond are the factors encouraging the incidence of this disease.
Dipping in 2 -3 % salt solution for 3 -4 minutes and pond treatment with a mixture of malachite green at the rate of 0.1 mg per litre of water and formaldehyde at the rate of 25mg per litre of water are the recommended control measures. Liming of pond for sanitation helps in controlling the disease. Proper feeding of the fishes is necessary to prevent as well as cure this disease.
2. Scale and body spot disease
The scale and body spot disease occur during pre/post and winter months mostly to the young ones of mrigal and rohu. It is caused by the protozoa called Myxobolus mrigalae and rohitae. The affected fishes show white cysts embedded in the scales and body surface leading to emaciation, degeneration of the scales and ulcer formation,
The presence of the spores of the protozoa, the excessive deposition of the decaying organic matter and the lack of proper feed are the aggravating conditions for the incidence of this disease.
The treatment for this disease is the same as those pre- scribed for the first protozoan disease.
Trichodinosis is a ciliate protozoan disease affecting all the Indian and Chinese carps during the post monsoon and winter months. Excessive secretion of mucus from gills and body, pale gills clubbed or worn out are some of the symptoms observed in the affected fishes.
The treatments for this disease are the same as those prescribed for the other protozoan diseases already described.
Chilomastosis is a disease caused by a group of organisms belong to phylum protozoa and class mastigophora. There are many types of mastigophora. They parasitize on different parts of the body and cause diseases. They can be prevented or eradicated by giving the same treatment explained for other types of protozoan diseases.
Ciliates are protozoans having hair like structures on their body, called cilia. The cilia are used for transportation, feeding, sensing, protecting etc. There are many types of ciliates which cause various .types of protozoan diseases to the fishes.
Coccidia are parasitic protozoans usually residing in the alimentary canal of the fishes and disturb the proper functioning of the digestive system thus digestion and absorption of the food materials. There are many species of coccidia causing various types diseases to the fishes.
Myxosporidiosis is the name used for a number of sick-nesses caused by a number of organisms belonging to the protozoa and its subdivisions. They cause various types of diseases to the fishes.
8. Microsporidia diseases
These are diseases caused by microsporidians which parasitize on the fishes. From the name itself we can understand that they are spore producing organisms to multiply themselves. Their infestation results in various types of diseases.
E. Helminth disease
Helminths are worm like organisms causing diseases to the fishes. Helminths can be round and long or flat and long. Trematoda diseases are caused by flat helminths or platyhelminths. The important helminth diseases are dactylogyrosis- gyrodactylosis, black spot and ligulosis.
1. Dactylogyrosis and Gyrodactylosis
The name of the disease and the name of the organism are the same. Both the Indian and Chinese carps are affected by these diseases. They infest the fishes during the post monsoon and winter months. Fading of the normal colour, dropping and folding of fins, feebleness and frequent surfacing are the symptoms observed. Excessive secretion of the mucus and damage of the epithelium of the gills are also observed.
Higher stocking rate and loss of appetite during winter are aggravating factors for the incidence of this disease.
Dipping treatment of the infected fishes for 3-4 minutes in formalin dissolved at the rate of 200 -250 mg in a litre of water or in 2-3% salt solution can control the disease.
2. Black spot
Black spot usually affects the Indian carps and is caused by the organism called Diplostomum spp and Dilostomulum spp. They usually infest the catla fishes during the post winter months. Black cysts are found allover the body of the fish. Excessive secretion of the mucus from the gills is noticed. The infected fish show signs of irritability and tendency to frequent surfacing.
This disease can be controlled by giving a bath to the infected fishes in 3-5 % solution of salt or in 200 ppm tormalin solution. Eradicatition of molluscan population tram the pond vicinity reduces the incidence of the disease.
Ligulosis is a helminth disease affecting the catla fishes. The infected fishes show abnormally enlarged abdomen and dark coloured body, Birds around the ponds is an aggravating factor for the spread of this disease, The causal organisms spread through these birds especially through their droppings. Therefore control of these birds itself is a means of controlling this disease.
4. Tape worms
The nature and functioning of tape worms is familiar to all. It is a deadly parasite in the sense that once it is infested it cannot get rid oft' easily as it can hide its microscopic head in the tissue of the host even if the body segments are detached.
F: Crostacean diseases
Crustaceans are the organisms with segmented body and jointed legs. Some of these are parasites on the fish causing diseases to the fishes. Argulosis, Lernaeosis and Ergasilosis are the three important crustaean diseases that infest the fishes.
Argulus sp is a crustacean organism affecting the Indian and Chinese carps during the summer and pre-monsoon months. The organism attaches itself to the body of the fish causing irritation and as a result we can notice rubbing behaviour of the fish, trying to get rid of the irritating organism. Continued infection leads to emaciation and pigmentation on the body surface. Excessive deposition of decayed organic matter at the bottom of the pond is an additional cause for the infestation of the disease.
Hence prevention of deposition of decayed organic matter is a prerequisite to control the disease. Pond treatment with gamrnaxine at the rate of 0.2 mg/litre of water or bath in 3% salt solution of infected fishes for 3-5 minutes are the measures that can control this disease.
Lemaeosis disease is caused by Lernae sp which affect the Indian carps. The incidence of this disease is found to be common in the summer months. The body of the infested fishes is covered with pin like white bodies allover. There will be excessive secretion of the mucus. Due to severe infection the gills may be damaged.
As in the case of other diseases described excessive deposition of the decayed organic material is one of the causes of infestation by this organisms.
The treatments for this disease is same as those pre- scribed for the other crustacean diseases.
Ergasilosis is a crustacean disease caused by Ergasilus sp and occurs mostly in the summer and winter months. The infected fishes appear restless, frequently coming to the surface and fading of the normal colour is seen. Excessive secretion of mucus and the gills becoming pale are other symptoms observed in the infested fishes. This disease also is encour- aged, as we have seen in other diseases, by the excessive loading of the pond bottom with highly decayed organic material.
This disease can be controlled by the same treatments as those prescribed for the other crustacean diseases.
G. Nematode diseases
Nematodes are microscopic type of worms that are found in the soil, plants and animals. Some nematodes live on fishes as parasites. Nematodes which parasitises on fish are divided into two: those which use fish as the final host and those which use fish as the intermediate host. Majority of the first ones resides in the alimentary canal while some in the gills, eye sockets, body cavity, muscles etc. So far the problems due to infestation of nematodes have not come up to any significant level. However, the farmers should be aware of the existence of such organisms that are harmful to the fishes.
H. Environmental diseases
The physical and chemical characteristics and general condition of water, temperature, amount of dissolved oxygen, amount of decayed organic matter accumulated etc. are the environmental factors that contribute to the growth and well being of the fishes positively or negatively.
If the amount of dissolved oxygen is less then the fishes show stress by gasping for air at the surface of the water.
If there is excessive accumulation of highly decaying organic matter then as we have already seen a number of diseases occur.
If the water is muddy or turbid the sunrays will not reach the bottom of the pond and the growth of plankton will be affected.
Similarly, if the water is too acidic or alkaline it will affect the fishes. For example, if the pH of the water is below 5.5 it becomes toxic to most of the fishes. And it the pH is at or below 5.00 mortality may start. There will be excessive secretion of the mucus, the body will be covered by a thin whitish film and the gills turn brownish in colour. Ponds with such low pH should be treated with 500 kg calcium carbonate (lime) per hectare. As far as possible run off water or water from the melted snow should not be allowed to enter the pond.
If the water is too alkaline (PH above 9.0) then also it is dangerous for the fish. The pH should be brought down to normal or slightly alkaline by the application of gypsum at the rate of about 250 to 500 kg per ha depending on the pH value of the pond.
Excessive shading, periodic flooding by the run off water, incoming of sea water into the pond, excessive drought and water scarcity are some of the other environmental factors that adversely affecting the health of the fish.
I. Nutritional diseases
Artificial feeding is the main source of feed for the fishes cultured in ponds. Over feeding as well as under feeding will cause diseases and mortality among the fish. In certain fishes over feeding results in Lipoid hepatic degeneration characterized by a yellow-brown colour of the liver. Treatment includes avoiding over feeding.
Entritis is a feeding disease. If we press the abdomen of the affected fish a yellow-red liquid will come out through the anus.
The feed should be balanced to supply all the essential nutrients to the fish in their proper quality and quantity. The feed should be distributed regularly at different locations close to the bank of the pond and ensure that all the fishes get sufficient feed and at the same time no excess feed is supplied at a time to avoid chances of overfeeding. For more details about feeding of the fish consult Booklet No. 525 on "Fish Feeding".
III. Pests of Fish
As for all the living beings so also for the fishes there are several natural enemies which are called in general pests.
Some of them are insects, amphibians, reptiles, bird, mammals and even fishes themselves. Among them some are permanent enemies (of eggs, fry, and adults) while others are occasional enemies and those competing for feed. However, they are described here under insects, amphibians, voracious fish, reptiles, birds and mammals.
The most note worthy among the handful insects are the water beetles, water bugs and dragon flies. They attack the eggs and fry. They also compete for feed. In some insects, only larvae are harmful while in other both the larvae and adults are handful.
a. Water beetles
Water beetles are 'found abundant in pond with lot of aquatic plants. The great diving water beetles is the most important among them. The adults of these beetles eat on the fry and are very voracious in nature. The larvae suck in the eggs and small try. They can do a lot of harm in the nursery ponds. The adults of black beetles, another harmful beetle, being vegetarians are not dangerous to the fishes however
their larvae are voracious eaters of eggs and fry.
As a preventive measure do not place nursing ponds under water more than 15 days before stocking in order so that harmful larvae have no time to develope. Secondly clean up swamps and grassy ditches in the neighbour hood of the fish farm.
b. Water bugs
Water bugs are of several types. They are harmful to the fishes at varying degrees: some eating up the eggs, some fry etc. But they are in real competitors for feed. Cleaning up of all aquatic weeds regularly will control the water bugs.
The nymphs of dragon flies are aquatic, though the adults fly in the air, and they can eat up eggs and small fry. Yearly drying of the pond is the best way to control the nymphs of the dragon flies.
The larvae and adult of the amphibians are harmful as predetors and competitors of feed. Frogs are the most harmful among the amphibians to fish. Some of the species of the frogs live on the fry while the tadpoles mostly eat on the eggs.
The adults and the tadpols can be scooped out using a scooping net. They also can be destroyed by quicklime.
Reptiles especially the crocodiles can destroy the eggs, fry and even the adult fishes of bigger size.
Kingfisher, grey heron, duck, swans, water hens and other water bird are predators of fish. Some of them prey on fry, some on eggs, some on the small and medium size fish and they do the harm at various degrees. These birds could be chased away using appropriate birds scarers or could be caught on suitable bird traps.
Otters (Lutra lutra), musk rats, brown rats, water rats and water shrew are some of the mammals that prey on the fishes. They live in the pond area in burrows on the sides of the pond. These burrows themselves are dangerous to the ponds. Several of them destroy or feed particularly on eggs and fry while others feed on adult fish. Among them the others live only on fish and they can do great harm. Use locally available methods to trap and eradicate the mammals.
6. Voracious fishes
By nature, some fishes are more voracious which can be noticed from the way they eat: eating fast and greedily. When such fishes are grown along with the less voracious fishes the latter ones will be at a disadvantage of getting less feed for themselves.
7. Carnivorous fishes
Carnivorous fishes are those which prey on other fishes eggs, fries or growing or adult ones. In each locality there are several types of carnivorous fishes and the fish farmer should identify them using the local peoples knowledge. Catfish is a ubiquitous carnivorous fish which can do a lot of havoc to the cultivated fishes.
From the description of the diseases and pests of the fish certain things are very clear.
Excessive deposition of decayed organic matter at the bottom of the pond leads to the incidence of a number of diseases though organic matter is essential for the maintenance of the flora and fauna in the pond. Annual or biennial emptying of the pond and removing the excessively deposited organic matter and allowing the bottom of the pond to dry for at least 15 days is probably the most important preventive measures to control most of the diseases. Secondly, sanitation in the surrounding area of the pond should be maintained. Thirdly the fishes should be fed properly with feed balanced in all the nutrients. Both over feeding and under feeding are harmful. Fourth: ensure that no animal burrow the sides destabilizing the side walls of the pond. Fifth: maintain the optimum range of pH of the water in the pond. Sixth: use only eggs and fries from uncontaminated breeding stock or from reliable nurseries. Seventh: ensure that no wild fish enter the pond. Eighth periodic bath of the fish with 3-4% solution of salt for 3 -5 minutes is very effective. Therefore at the time of the construction of the pond itself facilities for such baths and treatments should be foreseen. Ninth, provide antibiotics along-with feed as a preventive measure to most of the bacterial diseases. Tenth, regular liming of the pond should be carried out. If these ten points are put into practice the fish farmer can make sure of a successful crop of fish.