DILIP KUMAR
UNIT FOR ICHTHYOPATHOLOGY & FISH HEALTH PROTECTION
FRESHWATER AQUACULTURE RESEARCH & TRAINING CENTRE
(C.I.F.R.I.)
P.O. KAUSALYAGANG, VIA BHUBANESWAR - 2.
1. INTRODUCTION
India and many other southeast Asian countries remained very much concerned with the development of methods for increasing aquaculture production levels. In tensification of carp culture has no doubt helped in achieving this goal to greater extent, however, it has also propagated artificial stress to overcrowding, nutrients and metabolites accumulation, dissolved oxygen and other water quality problems. All such potential stressors have magnified the risk of outbreak of diseases and thus an integrated health management approach is needed involving eradication of pathogenic organisms, decreasing host susceptibility and correction of impaired environmental conditions, etc. (Kumar 1984). Such a radical management system of fish health is now becomming a decisive factor for the success of composite fish culture. It is high time to get aquainted with the commonly occuring diseases and the health management measures.
2. COMMON DISEASES
Carps are susceptible to many communicable and non-communicable diseases, the most significant among them are being described.
2.1 Communicable Diseases:
Manifestation of infections diseases in susceptible carp species is the combined action of potential pathogen and the stress caused by improper environmental factors. Potential pathogens are virus, bacteria, fungus, protozoan and metazoan parasites etc. Many fish may carry small numbers of pathogenic organisms either harbouring chronic, low grade infections or serving as carriors while in some cases it may account for sudden massive outbreaks of acute disease that sometimes occur when such fishes are subjected to stress.
2.1.1 Viral diseases: So far carps are concerned, mainly 3 viral diseases Spring Viremia of carp (SVC)/Rhabdovirus carpio (RVC), Epithelioma papillosum of carp and Gill necrosis of carp are of importance.
Spring Viremia of carp (SVC):
Spring viremia of carp (SVC) is an acute systemic viral infection caused by Rhabdovirus carpio(RVC) virus. The disease was known as infections dropsy of carp till the isolation of the virus from common carp (Fijan et al. 1971). Subsequently the dropsical syndrome was separated into spring viremia of carp (SVC), a condition caused by Rhabdovirus carpio and carp erythrodermatitis (CE) a condition caused by bacterial agents (Fijan, 1972).
RVC is a rhabdovirus pathogenic to carp of all ages and perhaps other cyprinids (Ahne, 1981). It has a typical bullet shape with fine surface projections in some cases. Genome consists of single stranded RNA covered over by a lipoprotein envelop. The virus particles measure approximately 120x60-80 nm(Ahne, 1981). Recently a new rhabdovirus has been detected in grass carp which seems to be a new serotype of cyprinid rhabdovirus. The main clinical signs are gathering of fish at water outflows, dark colouration, lower respiratory rate, petechial haemorrhages especially of the skin and gills, loss of balance, exophthalmia, inflamed vent etc. Internally they show haemorrhage in the viscera, air bladder etc. Frequently there is secondary invasion of the tissues by Aeromonads and Pseudomonads from the intestine resulting in the bacterial septicaemia which creates a state of confusion regarding etiology of the disease. Peritonitis with serous haemorrhagic exsudate is normally present in acute cases.
The virus is shed by faeces and possibly urine. Blood sucking parasites (Piscicola geometra and Argulus foliaceus) are vectors for SVCV. The virus is transmitted by water route and replication of SVCV has been demonstrated by fish in the gills (Ahne, 1978).
Swim-bladder inflammation (SBI):
This is another disease which affects both domesticated and wild stocks of common carp. The morphology, chemical composition, resistance to inactivating conditions and antigenic property of SBI isolates are identical to those of SVC (Liversidge & Munro 1978). Initially there is no typical symptoms but gradually they show a decreased flight reflex and stop accepting food.
Epithelioma of carp and gill necrosis of carp are two diseases with suspected viral etiology.
Epithelioma papillosum of carp.
The epithelioma papillosum of carp is localised epidermal hyperplasia of the skin of common carp and other cyprinids. The causative agent has so far not been isolated but herpes virus like particles in the hyperplastic epidermis of carp has been demonstrated by Schubert in 1964 and hence it is suspected to be of viral etiology. Infected carp shows white skin lesions which may spread to other parts of the body. Subsequently they loose balance and swim laterally - with a bent body. There are four progressive stages of the disease. The disease may have an acute course with high losses or it may be chronic with sporadic losses. In acute cases, the fourth stage of the disease is reached rapidly. Mode of transmission is still unknown but whenever it occurs it appears to spread throughout the population very quickly.
Gill necrosis of carp:
Gill necrosis of carp is a widespread disease of carp culture establishments. Among several suspected etiological factors such as lack of vitamins, water quality, intoxications, bacterial invasion etc., a viral etiology is also suspected. A cytopathogenic agent from carp, suffering from gill necrosis, has been isolated by Popkova and Schelkuvor (1978). The agent replicated in FHM cells at 28°C producing cytopathogenic effects such as rounding up of cells and inclusion bodies in the nucleus. Electron-microscopical studies revealed hexagonal particles. Further work is still awaited.
2.1.2 Bacterial diseases:
Among infectious diseases the role of the bacteria has been strongly emphasized as they present many practical problems in commercial aquaculture. They are responsible for heavy mortality in both wild and cultured fish. Since the actual role of these microorganisms may vary from that of primary pathogen to an opportunist invador, it is essential to establish its role as a primary pathogen to that of secondary invador. The true pathogenic role of the isolated bacteria is understood during the bacterial epizootics and through the experimental induction of the disease. Based upon Bergey's Mannual of Determinative bacteriology (8th Edition, 1974) the following groups are worth to be mentioned as most important bacterial pathogens.
| Family | Forms |
| Cytophagaceae | Flexibacter columnaris |
| (Chondrococcus columnaris) | |
| Pseudomenadaceae | Pseudomonas fluorescens |
| Vibrionaceae | Aeromonas hydrophila |
| Aeromonas salmonicida |
Columnaris disease:
The causative agent of columnaris disease is a long thin (0.5 to 0.7 × 4.0 - 8.0 um) Gram negative bacterium that moves by creeping or flexing action. It begins as an external infection with lesions appearing on body surface and the gills. The type of lesions varies with the fish species. As the disease progressed lesions spread and thus may cover most of the body. In rohu, neorotic lesions begin at the outer margin of the fins and spread towards the body. White ulcerations and haemorrhages may also be observed (Kumar et al. 1982). Bacteria apparently gain entrance to the dermal tissues as a result of injury, multiply in the connective tissues and reach the musculature where they form redulcerations. Erosion of the gill lamellae may also be observed. Disease outbreaks usually occur at temperature above 18°C. This disease is common throughout the world and affects virtually all species of freshwater fishes including various carp species.
The stress of crowding, handling or holding them at above normal temperatures, as well as the stress of the external injury, facilitates the transmission and outbreak of columnaris disease.
Bacterial Eye disease:
The occurrence of eye-disease of catla is found to be seasonal in nature with maximum intensity of attack during October, November and December (Gopalakrishnan 1961). Experiments made on the etiological agent have indicated that the organism grows well between 18°C and 24°C and hence post monsoon becomes suitable for the disease outbreak. The etiological agent, a Gram negative bacterium is a variant of Aeromonas liquefaciens. Eye is the primary organ of attack by the disease. Either one or both eyes may be affected. During the early stage of the disease a reddish colouration develops in the cornea due to vascularisation. This condition lasts for about 15-20 days and subsequently the whole of the cornea becomes opaque. Further progress of the infestation results is putrification of total eye tissues and ultimately the affected tissues fall of leaving behind the hollow eye cup. The gill colour also fades and most of the fish die by this stage. Brain and optic nerves are the other organs of attack.
Bacterial Haemorrhagic septicaemia:
Aeromonas hydrophila and Pscudomonas fluorescens are very close taxonomically and cause septicaemic diseases in carps and other species. The term haemorrhagic septicaemia is being used to designate septicaemic diseases caused by these two bacteria. The condition is usually clinically indistinguishable between aeromonad and pseudomonad septicaemia. Aeromonad infection is usually associated with concomitant stress caused by high temperature or overcrowding (Richards and Roberts 1978). The organism has also been particularly associated with secondary infection of carp species suffering from infection with Rhabdovirus carpio (RVC) virus (Fijan 1972). Dropsy condition among Indian major carps is a common bacterial disease. The etiological agent is a species of Aeromonas and by inoculating a pure culture of the isolate, the disease has been experimentally produced in fingerlings of catla, rohu and mrigal. The symptoms observed are more or less similar to those described in European countries. Recently several cases of dropsy condition in catla invaded by Aeromonos hydrophila and Myxosporidian spp. have been observed in rural ponds (Kumar et al. 1983). This mixed nature of infection creates a problem in deciding control and treatment measures as several drugs have been tried without a positive response on myxosporidian spores and cysts. Aeromonas hydrophila spp. hydrophila have been isolated at several occasions from diseased specimens of catla, rohu and silver carp from carp culture ponds in India. The haemorrhagic septicaemia may be acute or chronic, large haemorrhagic skin lesions are the most commonly observed signs and heavy mortality may occur very shortly after the advent of lesions. The main pathological changes are associated with the skin and haematopoetic tissues. In the skin the primary changes comprise hyperaemia of dermal vessels, with severe oedema extending in to lower epidermis but ulcerations follows quickly and the lesions also extend down into the underlying muscles. Recently a Pseudomonas fluorescens septicaemia in silver carp and big head causing heavy mortality has been reported in Hungary (Csaba et al. 1981).
Carp Erythrodermatitis (CE):
This disease (CE) is probably most widespread disease of common carp and several other species in European ponds. It occurs in spring and summer. The CE is actually the new name of the disease entity which is identified with acute form of IDC (Fijan & Petrinec 1973). After the development of skin inflammation hydrops appears and carps show exophthalmia, ascites, anaemia and edema of all organs. Aeromonas salmonicida complex has been assigned as causative agent of CE (Bootsma et al. 1977).
2.1.3 Parasitic diseases:
Parasitic diseases are usually encountered more frequently than microbial diseases. High level of organic matter due to increased fertilization and feeding and exposure to suitable temperature in carp culture ponds, shorten their life cycle causing extensive infection.
Protozoan diseases:
Protozoan diseases are among the most significant of all parasitic diseases in carps. Following are the most important parasitic protozoans parasitizing carp species.
Ichthyophthirius
“Ich” or white spot disease is probably one of the most detrimental parasites affecting all the species of Indian major carps and Chinese carps as well. The most common symptom is the presence of pin-head size white spots on the skin, fins and gills. It causes simple hyperplasia of the epidermal cells around the site of infection forming blisters. Ich is a ciliate characterized by its relatively large size and horse shoe-shaped nucleus in adults and large trophozoites. Incidence of large scale mortalities due to the infection is common in nursery and rearing ponds.
Trichodina:
Trichodina is another small saucer-shaped protozoan that harbour gills and external body surface. It is identified by ‘denticular ring’ of interlocking teeth and peripheral band of cilia. Excess mucus secretion is a common symptom of this infection. Epizootics are usually associated with poor water quality and high stocking density in fry and fingerling rearing establishments.
Costia:
A mastigophoran parasite Costia causing considerable damage is also observed in Indian major carps. This is a minute pear shaped parasite which are found attached to the gills or skin and produce a severe immitation with excessive micus secretion causing patches over the body.
Myxosporidian and Microsporidia spp:
Myxosporidian and Microsporidian parasitic infections are very frequent in major carp species. Reports of large scale mortalities of fry and fingerlings of carp species are common due to such infections. Several species of Myxosporidia have been found to infect all the carp species and form cysts on the body surface, fins, gills and internal organs like kidney and spleen. However, the damage is more when large number of cysts are present on the gills and the breathing of the fish is adversely affected. Renal infections lead to the damage of most of the renal tubules in the form of vacuolar degeneration of the tubular epithelial cells. In most cases the nuclei of the infected epithelial cells become pycknetic (Mishra et al. 1982). Microsporidian infections are most common in catla among Indian major carps. The parasite harbours the intracellular spaces of the epthelial cells of the renal tubules. The most common symptoms of the disease are weakness, emaciation, scale protrusion, loss of scales, abnormal pigmentation etc. In some cases deposition of haemosiderin pigments has been detected with carps suffering from Aeromonas infection and Myxosporidia invasion (Dey et al. 1985).
Worm diseases:
Worm diseases are caused by trematodes, cestodes and leeches. Many of those parasites do not apparently cause much harm to carp species, however, some have been know to be of serious concern. Among monogenetic trematodes. Gyrodactylus and Dactylogyrus are important as they cause sometimes very serious infections. Gyrodatylus infects skin and gills whereas Dactylegyrus affects only the gills. Carp larvae and fry up to the weight of about of 3 g are more prone to the infection and sometimes it may result in heavy losses. Excessive mucus secretions, decolouration of body, dropping of scales and faning of gills are the most common symptoms.
Most common among digenetic tremotodes is the Diplostomum spp. causing black-spot diseases in Indian and Chinese carps. Black spot disease is characterised by presence of numerous small black nodules or cysts all over body of the fish.
Several genera of cestodes have been found to infect major carp species, though apparently causing little harm. However, Brothiocephalus infection in common carp is becoming an important menace in nursery and rearing ponds in many European countries including Yugoslavia and Germany. Infected fish appears dull and sickly. Another important member of this group of fish parasites is Ligula in testinalis. It causes abdominal distension and in advanced cases it may break the body wall.
So far there is no report of any large scale mortality of carp species due to Acan thocephala spp. attack. However, all the three major carp species have been reported to be prone to Acan thogyrus acan thyogyrus infection. Leeches and nematodes also infect various carp species but the extent of damage caused by them is not up to alarming level.
Crustacean diseases:
Two important crustacean parasites are commonly found parasitizing major carp species. These are Lernaea (anchor worm) and Argulus (fish louse). Argulus attaches itself to the body of the fish by means of suckers and hooks but it can also swim freely in water. Several instances of argulosis associated with mortality of major carp species have been reported. Infected fish become very weak and emaciated. The common symptoms of argulosis are stunted growth, loose scales, haemorrhagic spots on the body etc. Lernaea frequently attack almost all the species of major carps and sometimes cause large scale damage in nursery and rearing ponds. It is a minute rod-like external parasite which attaches itself to the host fish anywhere on the body by means of anchor like appendages present on the head of the parasite. Its anterior portion is buried deep into the skin of the fish and only the posterior portion is visible hanging. In carps, usually the female parasite causes mechanical injuries which may eventually lead to secondary fungal or bactereal infections.
Fungal Diseases:
Mycotic fish diseases are only sporadically causing problems. Species of the general Saprolegnia and Branchiomyces are usually implicated in fungus infection but these are considered to be secondary invaders following physical or physiological injury brought about by rough handling or attack by primary pathogens. Saprolegnia infection is characterized by white brownish cotton ball like growth which consists of filamentous mass (hyphae) occurring on any part of the body. Injury produced by spawning, netting, crowding or lesions caused by other diseases are the common sites of initial saprolagina infections.
Branchiomyces is another filamentous fungus which obstructs the blood vessels in the gill filaments. Occurrence of flecking on the gill filaments which at a later stage becomes greyish-white and may finally drop off altogether leaving the cartilagenous support exposed.
Non-communicable Diseases:
There are several diseases which are of non-infectious nature. Such diseases are associated with various environmental, genetic or food factors. Common diseases of this category are discussed hereunder:
2.2.1 Gas-bubble Disease: This disease has been observed clinically in a number of culturable species including major carps. (Alikunhi et al 1951). This disease is associated with the supersaturation of the water with nitrogen or oxygen. In the pond, heavy algal blooms causing excessive gas generation brings about the outbreak. However, the physiological mechanism is still incomplete. It is more common in in larval stages where gas bubbles are found in the subcutis and the yolk-sac. In older fish, bubbles are found most frequently in the eyes, skin and the gills. Transferring affected fish in ponds with good water quality helps in curing the disease.
2.2.2 Liver lipoid Disease: Fatty degeneration of the liver due to malnutrition or detoriated feed have been found in many culturable species including Indian major carp Catla catla (Mishra and Kumar 1984). The disease if not treated in time, often cause unexpected large-scale mortality. Extensive replacement of liver cells by fat resulting in the destruction of parenchyma causing mortality has been found in catla.
3. HEALTH CARE
Fish health management measures which have to be followed for preventing and controlling disease outbreaks involves the following three major steps aiming towards attacking all the three interlinked causative factors - pathogen, host susceptibility and the environmental stress.
3.1 Management of Rearing Environment
Proper management of rearing environment offers optimum environmental conditions for the growth and better health of the cultivated fishes. It also strengthen the defense mechanism of the fish body to fight against invading disease producing organisms. Eradication of predatory and weed fishes, disinfecting the pond, selection of quality and healthy seed for stocking, maintaining proper species ratio and stocking density, water quality regulation, proper feeding and proper handling are the various steps of this management measure.
Poisoning of wild fish and disinfection of pond:
Wild fish are one of the potential source of fish pathogenic organisms. Some of these wild species are predatory in nature and prey upon the young ones of cultivated carp species whereas unwanted weed fishes rapidly multiply and compete for food with the cultivated ones- and hence the pond be kept completely free of such wild fish species. This is done by poisoning or dewatering the pond. Piscicides of plant origin are preferred over common chemical insecticides used in agriculture due to its long lasting toxicity and residual effect of the later. Moreover the fishes thus killed by such insecticides become unfit for human and animal consumption. On the other hand piscicides derived from plant such as mahua oil cake is most commonly used as its toxicity lasts for about two weeks and the fishes thus killed are fit for human consumption. It is applied @ 200–250 ppm. However, such poisoning process kills only the unwanted fish species of the pond but without affecting the existing fish pathogenic organisms. Disinfection of water is an effective means of disease control in fish culture by reducing the numbers of pathogens to minimum level.
If possible, disinfection of ponds should be attempted which can be done by liming @ 1500–2000 kg/ha with quick lime (CaO). Chlorination method using chlorinated lime (bleaching powder) @ 30–50 ppm is the most suitable and practical method for disinfecting undrainable ponds as it disinfects the pond water and soil and kills the existing unwanted predatory and weed fishes as well and hence this practice is becoming more popular due to its dual role and economy (Sinha and Kumar 1979).
Water quality regulation:
Some of the physico-chemical parameters of water have their direct influence upon the fish health. Any abrupt and wider fluctuations of such values often cause state of stress in fish resulting sometimes in widespread disease outbreaks. Dissolved oxygen content, pH, turbidity, temperature, introduction of some chemicals, detergents, pesticides and naturally produced toxic products like hydrogen sulfide, ammonia, dinoflagellate toxins etc., are most potential stress related parameters. Excessive application of inorganic fertilizers and accumulation of organic matter in older ponds may cause over production of phytoplankton, appearance of algal and bacterial bloom etc., leading to dissolved oxygen (DO) depletion to lethal level. For health and optimum growth the D.O. level should not drop below 2–5 mg/l. Carbon dioxide concentration upto 20–30 mg/l can be tolerated by fish provided oxygen is near saturation. At lower levels of DO the toxicity of carbon dioxide increases. The optimum pH range is between 6.7 and 8.6 liming agents may be applied to correct low pH. Ammonia concentration above 1 mg/l indicates organic pollution. Hydrogen sulfide toxicity increases with decreasing pH and it is harmful even at 1 mg/l concentration level. Making the pond environment more cogenial and hygenic eliminates the risk of stress and provides safety to fish. Proper and timely management of soil and water by manipulating feeding, fertilization, liming, addition of water, aeration, bottom recking, etc., eliminates most of the environmental stressors and provides better and healthy environment for the healthy growth of fish.
If possible the pond may be dewatered as it eliminates all the unwanted species of fish and other animals such as insects, molluscs, tadpoles and frogs at the same time sun drying of the bottom is an effective disinfection method. For making it more effectives freshly dewatered pond bottom should be treated with bleaching powder @ 500 – 1000 kg/ha and then left to react for 7–10 days before refilling it. An interval of 5–7 days between the end of filling the unit with water and the stocking eliminates most of the obligatory pathogens from the environment.
Selection of stocking materials and population regulation:
It is advisable to stock the pond only with healthy and genetically vigrous fry and fingerlings so that they may have better immunological status, better growth rate and resistance towards some diseases. Before stocking, proper sample size should be examined to check their health status. Overcrowding may lead to biological crowding resulting in waste build up, decreased availability of feed and dissolved oxygen, deterioration of water quality etc., and hence it is advisable to stock 5000–6000 nos. of fingerlings each hectare of water spread area.
Proper feeding:
Proper management of the undrainable pond ecosystem ensures sustained production of natural fish food organisms. However, the amount is not enough to support the high stocking density of fish in composite fish culture and hence adequate amount of quality feed is to be supplemented from out side. Supplementary feeding @ 2–3% of body weight on daily basis is necessary for proper health and faster growth of the fish. Any reduction in quantity and quality detoriation of feed may cause various deficiency and nutritional diseases including Liver lipoid disease (LLD) at the same time it will also increase the susceptibility to many other infections.
Reduction of handling stress:
Rougher the handling, the greater is the stress and the risk of outbreak of infectious diseases. Proper care should be taken not to break the protective mucous coating of the skin. High temperature causes additional stress and hence hauling, netting or transporting should be avoided during hot weather conditions.
Size seggragation of the stock and removal of dead fish:
Year or more than year class or brood fish many times serve as a carriers of disease causing organisms without exhibiting any clinical symptom of the disease. It happens that they become survivors of occuring epizootics due to built up immunity but retain few of the pathogens which when come in contact may infect small size group. To avoid such risk it is advisable to separate the young from the bigger size group or brood stock.
3.2 Prophylactic Treatment Measures:
Prophylactic measures includes chemoprophylaxis and immunoprophylaxis which are presently being employed for reducing and preventing infections.
Chemoprophylaxis: Application of drugs to prevent the outbreak of the disease is termed as chemoprophylaxis. This measure is very effective when a particular disease outbreak is anticipated (Kumar et al. 1982). Several methods of application of drugs such as oral and parenteral routes for prophylactic treatment are employed depending upon circumstances, existing facilities and experience. Dipping the fish into a concentrated solution of the drug for about 1 minute, short bath by stopping water flow and releasing high concentration of drug and allowing the exposure for about an hour or so, long bath and feeding medicated feeds to the fish are some of the common methods employed for prophylactic treatment.
Prophylaxis has its values at every stages of composite fish culture right from prestocking to stocking and rearing stages. It is advisable to have second poisoning of pond with malathion @ 0.25 ppm 4–5 days prior to stocking. It eliminates most of the crustacean parasites, some of which also serve as vector for some viral pathogens (Kumar. 1984). Dip treatment of fingerlings in 1000 ppm solution of potassium permanganate for few seconds before releasing them in to pond is also a effective prophylactic measure. Occassional application of potassium permanganate @ 2 ppm is recommended for increasing depleting D.O. level and also for reducing microbial load. Prophylactic use of penicillin @ 20,000 I.U. and streptomycin 25 mg/kg of fish have been found to be very effective in preventing outbreak of columnaris disease in rohu in a field designed experiment (Kumar et al. 1982). Feeding antibiotics with feed has successfully prevented the occurance of CE in European carp culture establishments. Prophylactic treatments of ponds with diptrex (0.4 kg/ha of active ingredient) or Bromex (0.12 kg/ha of active ingredient) successfully prevents the occurance of trematode and copepod infections. Treatment is applied twice.
Immunoprophylaxis: Rapid progress has been made in research on the immune system of fish and in the development of immunization techniques against some of the most common infectious diseases and as a result vaccines against vibriosis, enteric red mouth, ferunculosis and SVC are available commercially. These vaccines do not provide absolute protection from infection but do help fish combat infections sufficiently to make immunization cost-effective-in many situations where these specific diseases cause repeated problems. Vaccines against SVC or RVC is administered in year class carps before releasing them in stock ponds. (Kumar 1984).
Therapeutic Measures:
The third major area of health care in the situation of disease outbreak is the therapeutic measures aiming at supressing, eliminating pathogens. There are five methods of drug application for treating any disease outbreak. These are through injection, feed additives, dipping in concentrated solution of therapeutic, prolonged bath and indefinite pond treatment. Some of the general treatments for specific groups of pathogens are described in brief.
Viruses: No treatments are known for virus diseases.
Avoidance and prophylactic measures are best ways.
Bacteria: Bacterial infections are treated in all the three ways i.e. by external treatment, systemic treatment via diet and parenteral treatment via injection.
Terramycin (Oxytetracycline) supplemented with feed @ 7.5 g/ 100 kg/day for 10–15 days controls systematic bacterial infections, bacterial haemorrhagic septicaemia etc. A withdrawl period of 21 days is necessary before the fish are marketed. Via injection its dose should be about 20–30 mg/kg of fish. Sulfa drugs such as sulfamerazine and sulfamethazine is applied with the feed @ 250 mg/kg body weight for 2 weeks to control ulcers, nephritis, columnaris disease etc. Combination of penicillin and streptomycin works as broad spectrum antibiotics and controls columnaris, bacterial haemorrhagic septicaemia and other systemic bacterial infections when applied @ 20,000 I.U. of penicillin and 25 mg of streptomycin/kg body weight through parenteral route. Chloromycetin is used in similar way as terramycin. Nifurpirinol has been reported to be very effective for the treatment of all myxobacterial diseases at an active concentrations of 1 mg/lit for one hour bath. It has the advantage of being absorbed through the gills and acts both externally and systematically. Erythromycin fed @ 4.5 g/100 pounds for 2 weeks and several of the Nitrofuraus - Furæzone, Furacin, Furanace etc. @ 10 g/100 pounds for 10 days controls most of the bacterial infections.
Potassium perman ganate used in pond treatment @ 2–3 ppm gives good results against bacterial outbreaks. When fishes stop feeding and it becomes difficult to apply antibiotics through feed this treatment method acts reducing bacterial population of water and also oxidize organic matter the bacteria thrive upon.
External parasites : The most problematical external parasites are the protozoans, gill flukes and crustaceans. Formalin is one of the best treatments for protozoans and gill flukes. Effective rates are 15–25 ppm as pond treatment and 100–250 ppm for 1 hour exposure as prolonged bath. At higher temperature lower limits should be used. Malachite green used @ 0.1 ppm has been used to treat Ichthyophthirius or Ich. A combination of formalin (25 ppm) and malachite green (0.1 ppm) gives excellent results. Malachite green is being used as a dip treatment to control fungal infections. KmNO4 is also used to treat the external protozoan parasites @ 2–4 ppm in ponds, @ 10 ppm for 20–30 minutes as bath and @ 1:1000 for 30 seconds dip treatment. Salting fish using common salts is one of the traditional method for treating external parasites. Few minutes dip in 3% salt solution is helpful in combating the disease. Acetic acid has been used for 1 to 2 minutes dip treatment (1:500 concentration). Dylox an organ ophosphate insecticide has been found to be effective as a control for Lernaea and other crustaceans when applied @ 0.25 ppm (active ingredient). It is also effective as a treatment for gill and body flukes but it is not effective against protozoans. Gammexane is also effective against such treatment when applied in pond @ 1–5 ppm. Copper sulfate has also been used to treat certain protozoans at a rate of 1 ppm but the total hardness of the water should be above 25 ppm to be safe.
Internal parasite : Most of the problems caused by internal parasites in carps are by and large by myxosporidians, microsporidians and tissue-inhabiting larval forms. There is no known treatment for myxosporidians. Recently several potential antiprotozoan drugs have been tried against renal myxosporidiosis but without any success (Mishra et al. 1984). Most of the parasites inhabiting the alimentary canal can be controlled by use of an antihelminthic, Di-N-butyl tin oxide. This compound is given in feed @ 1% of feed.
Precautionary Considerations :
Drugs and chemicals are often used to correct errors in management. While this practice can be used as a stop-gap, it cannot be used to prop up poor culture programme. Sound husbandry is the best approach to disease control.
Indiscriminate feeding of low levels of antibiotics will remove only those bacteria most sensitive to the drug and can lead to the development of drug resistant strains. Drug resistant bacteria can transmit this resistance to other bacterial species that have never been exposed to the drug. Therefore treatment with antibiotics should be only at prime need.
It is better to stop feeding 1–2 days prior to medication through feed. Never treat the fish within 4 hours after feeding.
Always watch for signs of stress a unexpected toxicity.
Monitor D.O. levels before and during treatment. Fishes are stressed during treatment and their D.O. need is increased.
A small group of fish should always be treated first before treating the whole lot with a new compound or formulation or using a product for the first time.
Calculations for dilutions of the drug should always be rechecked.
Antibiotics such as Terramycin which is a water soluble and may leach out of the feed unless preventive steps are taken. It is best to suspend such drugs in oil when preparing medicated feed (Cod liver oil seems to have better palatability than soyabean oil). The daily ration of feed can then be coated with oil/antibiotic mixture.
Once treatment has been started, rigidity should be maintained to dose and treatment schedule even when mortality has been stopped.
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