THA/75/012/WP 5
PRELIMINARY LIST OF DISEASES OF CULTURED
CLARIAS IN THAILAND
CLARIAS IN THAILAND
|
THA/75/012/WP 5 PRELIMINARY LIST OF DISEASES OF CULTURED CLARIAS IN THAILAND |
by
National Inland Fisheries Institute, Thailand
and
Institute of Aquaculture, Stirling, Scotland1
Programme for the Development of Pond Management
Techniques and Disease Control (DoF - UNDP/FAO THA/75/012)
Thailand
National Inland Fisheries Institute
Bangkok, Thailand
1981
The “Programme for the Development of Pond Management Techniques and Disease Control (THA/75/012)” was implemented in Thailand during 1979–82 as a joint project by the Department of Fisheries (DOF) and UNDP/ FAO. The purpose of the project was to improve DOF support services for Clarias farming through strengthening:
the skills of Fisheries staff in aquaculture disciplines such as disease diagnosis and treatment, pond management and extension,
the research on solutions for problematical aspects of Clarias culture,
the system of relaying problems from the farms to DOF and of transferring improved technologies, and
the equipment and facility base of DOF for working on aquaculture problems.
Although the UNDP/FAO participation was structured to terminate in August 1981, DOF committed continuation of the project to at least August 1982.
This report is one of several Working Papers prepared on various aspects of the project. A list of titles of reports completed in the series is annexed.
Inquiries concerning the subject matter of any particular report should be directed to the author,
c/o The Director
National Inland Fisheries Institute
Kasetsart University Campus
Bangkhen, Bangkok 9
Thailand
Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.
This electronic document has been scanned using optical character recognition (OCR) software. FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.
2.1.3 Henneguya sp. and Hyxobolus sp.
3.3 Bacterial Ulcerative Disease
4.3 Bone Rarefaction Spinal Deformity
PRELIMINARY LIST OF DISEASES OF CULTURED CLARIAS IN THAILAND
National Inland Fisheries Institute Thailand
and
Institute of Aquaculture Stirling, Scotland1
The diseases of cultured Clarias has been of topic of continuing study by the National Inland Fisheries Institute, Thailand, for a number of years. A concerted and comprehensive investigation of the subject was implemented in 1980 by a joint study team comprising the standing Thai pathologists and pathologists from the Institute of Aquaculture, Scotland, under the DoF-UNDP/FAO “Programme for the Development of Pond Management Techniques and Disease Control (THA/75/012)”. The report herein presents of preliminary list of parasitic, bacterial and nutritional diseases disclosed by the investigation. The information derives from the inspection of Clarias drawn from various farms in Thailand by the joint team in 1980 and from Thai fisheries records. The list constitutes of contribution to a more complete account of Clarias diseases that is presently under development by the team.
Ian MacPaG
Randolph H. Richards
Ponald J. Roberts
Christina Sommerville
of the Institute of Aquaculture University of Stirling, Stirling,
Scotland.
Three categories of parasites were found in the fish:
those considered to be or capable of being primary pathogens, responsible for severe damage to the fish;
those unlikely to be of pathogenic function per se but indicative, when present in large numbers, of either excessively deleterious water quality which allows them to thrive on the fish surface, or else some stress factor such as nurritional deficiency or skin wounds, which reduces the resistance of the host.
those observed to occur occasionally but considered to represent the normal parasites of Clarias and not likely to cause any adverse effect.
The parasites considered to be primary pathogens and the likely causes of clinical diseases were.
Those protozoan parasites, of a variety of species yet undistinguished, are well recognised as fish pathogens, although generally on young fish. This was apparently the case with the Thai Clarias. Specimens of young fry frequently had massive numbers of these protozoa on their gills and skin and it was considered that this protozoan parasite is an important primary pathogen of young cultured Clarias. Occasionally, in heavy infections, the auxiliary breathing organ was also affected.
These monogenean parasites were found on the skin, fins and gills, often in significant numbers. It is recognised in most intensive culture systems that this parasite can increase prodigiously under certain circumstances and may be directly responsible for massive fish losses.
Myxosporidan cysts were found on the skin and fins of larger fish without apparent clinical effects. However, heavy infactions of fry have been recorded in isolated cases which causes serious problems in fry ponds.
Monogeneans of the Family Dactylogyridae w were common on the gills and occasionally, large numbers were even on healthy fish. Some were observed in the buccal cavity but this is not considered a normal site for these flukes. At least two species and possibly more than one genus were found on the same host. Actinocleidus sp. and Ancyrocephalus sp. have been recorded from the gills of Clarias macrocephalus and Clarias batrachus, respectively.
This group comprises sessile peritrichs such as Carchesium, Ppistylis, Scyohidia, Vorticella, etc. These and also Chilodonella, which were most frequent in massive numbers on depressed fish. They were also commonly associated with traumatic or bacterially induced skin lesions.
The scyphidians are generally accepted as being non-pathogenic and as indicators of a depressed state of health of fish. Often they coincide with poor water conditions and overcrowding, which result in increased availability of food for these parasites. Eowever, where they accumulate on ulcerated areas they almost certainly inhibit re-epithelialization and thus contribute to osmotic damage. The fact that they were found so frequently indicates how closely stocking densities and water quality in the Thai system approach danger level.
Saprolegnia are well recognised as secondary infectors of all types of piscine skin lesion. Though not seen with great frequency on live fish since most skin lesions had heavy myxobacterial and scyphidian flora rather than Saprolegnia, such infections were seen in a few cases. Fish which succumbed for any reason, however, were rapidly invested with an enveloping layer of Saprolegnia fungus within hours.
Myxosoma/Myxobolus cysts were seen in gonads of larger fish. Myxidium sp. was similarly found in the gall bladder and intestine of such fish and Henneguya sp. was found on the skin surface. However, these were not considered to be particular clinical significance except as a reservoir of infection for the serious infections of young fish described in Category A.
Tapeworms were never present in large numbers, although they were occasionally seen in the intestine or else encysted in the abdominal cavity. Gangesia sp., a proteocephalid has however been recorded from Clarias macrocephalus.
Small numbers of nematodes were observed in the intestine. The following species have been recorded: Procamallanus planoratus,Camallanus ophicephali (third stage larvae), Contracaecum spp. and ascarid larvae from the intestine of Clarias macrocephalus, Camallanus anabantus and Procamallanus sp. have been recorded from the intestine of Clarias batrachus.
Acanthocephalus sp. has been recorded from Clarias macrocephalus.
Small numbers of adult Digenea were found in the intestines of both fry and broodstock. Only single worm infections were recorded from both fry and broodstock. Gauhatriana batrachii has been recorded from the intestine of Clarias macrocephalus and Orientecreadium batrachoides from the intestine of Clarias batrachus. Metacercarial cysts were occasionally seen in the gills of fry but usually in small numbers.
The most significant bacterial disease was acute bacterial specticaomia, which has been recorded frequently from the Thai culture systems. In the cases observed the responsible microorganism was Aeromonas hydrophila but pseudomonads were also occasionally involved. The pathology of the lesions indicated a generalised infection with major lesions in gut, spleen, liver and kidney haemopoietic tissue. Skin lesions were seen, but were deep and unlikely to be primary. This infection is likely to be of water borne origin. Usually it is associated with high water organic levels and is probably the most frequent cause of heavy losses in epizootics. Examination showed that the responsible organism was sensitive to chloramphenicol only.
Occasional fish of all ages were found to have areas of liver necrosis associated with bacterial infection where there was no other focus of infection. No bacterial isolation was carried out on the lesion.
This condition may well have had a number of differing bacterial aetiologies, but it is suspected that the primary stimulus in each case is traumatic ulceration either when fighting, at overcrowding around single site feeding stations (which should avoided) or from bird or other predator damage. The lesions were invariably deep dermal ulcers with severe bacterial necrosis and an overlaying congery of necrotic tissue, saprophytic parasites and bacteria such as Myxobacteria. Isolation of significant bacteria from lesions such as this is very difficult due to the degree of contamination, but it seems likely that aeromonads and pseudomonads are the main seconslary infectants.
The development of a new industry, at the rate at which the Thai Clarias catfish industry has expanded is bound to sootlight problems associated with husbandry factors such as water quality and diet. The dietary problems of Clarias culture in Thailand stem from the situation where trash fish which is the principal input food is now less reliable because of external factors such as increased oil prices. As a result, efforts to produce a substitute diet have been made, which, in the present state of lack of dietary information, seem to have resulted in conditions which are of direct induction. As pelleted diets improve these will disappear, but for the present, conditions associated with diet are presented below.
This is a condition where there is an under running of the head bones, from the rear, which may result in secondary bacterial infections. The condition seems to be related to the feeding of skinless rice as a high proportion of the diet and to the water quality. X-ray examination reveals evidence of an osseous dystrophy or rarefaction, the lesion appearing to be confined to the junction of bone and soft tissue at the back of the head. Vitamin C deficiency in rapidly growing fish is postulated as a likely cause.
One particular outbreak of spinal deformity has been studied in some detail in fish from a culture operation near Minburi. Approximately 50% of the fish in one pond had severe spinal deformity, which resulted in marketing problems. X-ray failed to reveal any anomaly of the spinal vertebrae apart from their displacement. Histology showed that the muscle was quite normal but there was spinal cord demyelination and osssus dystrophy. The exact aetiology is unknown. It is unlikely to be congenital and a toxic or deficiency aetiology is the most likely aetiology. Possibly this represents another manifestation of vitamin C deficiency.
Another outbreak, appearing clinically similar to the above, took place in both groups of fish fed on pellets and trash fish. Histology showed that these fish had a rarefying osteitis associated with fracture and haemorrhage. Such lesions are usually associated with vitamin C deficiency. Analysis of the pellets being used revealed levels of vitamin C which are below the recommended levels for dietary vitamin C for catfish.
This condition, which took the form of severe abdominal accumulattion of interstitial tissue fluid, was common in young fingerlings from certain sites. Unfortunately, the dropsy was unaccompanied by any tissue lesion. A nutrition/metabolic lesion is a possible cause although occasionally Aeromonas hydrophila could be isolated from the ascitic fluid. There was no histopathological evidence of viral damage such as is observed in channel catfish virus disease.
Although the pattern of diseases was as might have been predicted, the main feature of the study was the very considerable lack of clinicopathological material. Considering the density at which fish are held and the very severe constraints on water supplies, the gills and skin were generally in very good condition. Apart from the ulcerative or parasitic conditions indicated, no major skin lesion was seen, and spongiosis or occasional hyperplasia were the only dermatopathies seen except in one experimental fish presented by the nutrition department at NIFI where the dermis showed severe fibroblast swelling and lack of collagen, suggesting vitamin C deficiency. Apart from fry, the gills were generally excellent although hyperplasia and lamellar dystrophy was found especially in parasistic infections. No lesions of the auxiliary breathing organ were to be found other than rare cases of trichodinid infection. Considering the variable quality of the food, the muscle, in particular, was very good histologically. Trash fed fish and pellet fed fish, however, had very fatty livers which occasionally were so extreme that they should be considered pathological.
Pellets are going to be important for the development of the industry, but it would seem that considerable work is still required before a completely satisfactory pellat is available. Fish fed on pellets often had, apart from the liver lipidosis indicated above, a cardiac myopathy deficiency of haemopoietic tissue of spleen and kidney. Although not serious, these findings suggest the need for further study. There was also, in some pellet fed fish, a distinctive, non-infectious hepatic necrosis which could be sericus for growth and food conversion if it was a general occurrence. Spinal defermities were not at all uncommon and some at least were also of nutritional origin.
The Programme for the Development of Pond
Management Techniques and Disease Control
(DoF-UNDP/FAO THA/75/012)
REPORTS
THA/75/012/WP 1 Report on Aquaculture Training Undertaken at the International Center for Aquaculture, Auburn University, U.S.A. Chanchai Sansrimahachai
THA/75/012/WP 2 Third Semi-Annual Report (Sept. 1/80-Feb. 28/81) of Progress on the “Programme for the Development of Pond Management Techniques and Disease Control (DoF-UNDP/ FAO THA/75/012)” Alex N. Fedoruk
THA/75/012/WP 3 Management in Clarias Culture, Thailand. James Muir
THA/75/012/WP 4 Collecting Clarias Fry from Natural Waters. Montree Muangboon
