HEALTH AND DISEASE STATUS OF CULTURED GULSHA (Mystus cavasius) AT MYMENSINGH REGION OF BANGLADESH

Received 12 March, 2020 Revised 09 April, 2020 Accepted 12 April, 2020 Online 30 April, 2020


INTRODUCTION
Mystus cavasious locally known as 'Gulsha' has been drawing attention of fish farmers in Bangladesh due to its high market value, profitable culture, good taste (Saha et al., 1998). For this reason, farmers of greater Mymensingh region are culturing these fishes to a large extent. Gulsha is a carnivorous fish, feeding on insects, larvae and small fish (Islam and Azadi, 1989). The fish commands higher and more lucrative price than Indian major carps and other table fishes.
Disease has become a major problem in fish production in culture system and wild condition in Bangladesh (Rahman and Chowdhury, 1996). Due to increased production, making a large profit at a short period of time and consumer demand, farmers culture most of the species including gulsha in a very high stocking density. In pond aquaculture system, high stocking density and irregularly feed supply is very prone to disease outbreak. As a result, fishes are subjected to be stressed and diseased. A very wide range of diseases and parasites affects gulsha particularly when they are under stressed from poor environmental condition and in inadequate nutrition. Most common symptoms of diseases are hemorrhage, necrosis, pyknosis, hypertrophy, gill damage and different kinds of lesions (Ahmed et. al, 2004). Clinical signs and histopathology are important tools in diagnosing fish diseases. A total lack of mucus, edema, enlarged abdomen, growth of nodules on the body surface, presence of yellow, white or black spots on the skin, prolapsed anus and exopthalmia are all clinical signs of fish diseases (Plumb,1994). Histopathological study is not only used in pathogen identification but also facilitates to study of pathogenesis. The progress of disease development as well as the cause of determination of death can be studied through this technique.
Histopathological technique is one of the most important procedures for disease diagnosis in fish. It has been successfully used throughout the world. Prevention and control of diseases in aquaculture are a function of appropriate and quick disease diagnosis and proper health management. In pond aquaculture system, high stocking density and irregularly feed supply is very prone to disease outbreak. Most pond fish farmers do not have a good understanding of health and disease issues in their system.

Study area
The study was consisted of both field and laboratory investigation. The field study was conducted in four upazilas of Mymensingh region during January to April (2019). The upazilas were placed in Fulbaria, Nandail, Muktagacha, Trisal and Mymensingh sadar under Mymensingh district of Bangladesh ( Figure 1).

Data collection method
Data was collected through the questionnaire interview from 8 fish farmers. A set of questionnaire was prepared. The questionnaire focused mainly on the status of farming systems of Mystus cavasius. For questionnaire interview a set of questionnaire was developed composed of open form of questions.

Sample collection for health and disease investigation
The sampled fishes were examined just after taking out of the container to observe external signs and record any injury, infection and other abnormal conditions of fish body through naked eye. Samples from fish muscle, gill and liver were collected by sharp scalpel and forceps and fixed in 10% buffered formalin. Then samples were dehydrated, cleared and infiltration through an Automatic Tissue Processors (Citadel-1000), sectioned and stained with hematoxylin and eosin stains. The tissue sections were examined under a photomicroscope. Thus comparisons were made based on seasons and areas following health status of gulsha.

Clinical Observations of M. cavasius in winter and summer season
Reddish lesions at the ventral side of head region were recorded from fishes of Sharnalata Agro Fisheries in the month of February (Figure 2), whereas, severe reddish lesions and mild injury were observed at various parts of the body from fishes of Reliance Aqua Farm in the month of January (Figure 3). Abrasion and white spots were found from fishes of Chan Miah Fish Farm in the month of February (Figure 4), whereas, deep reddish lesions in ventral side and opercular region were found from fishes of Fish Seed Multiplication Farm in the month of January ( Figure 5).
Clinically, more or less normal fish were observed from Setu Hatchery and Aquaculture and Fish Seed Multiplication Farm, Maskanda in the month of March (Figures 6 and 7). However, Normal healthy fish was observed from Nuha Aqua Farm and Sharnalata Agro Fisheries Farm in the month of April (Figures 8 and 9).

Histopathological observations of liver in winter season
In the month of January from Shornolota Agro Fisheries Farm and Relience Aqua Farm, the liver of M. cavasius had fat bodies and vacuum (Figures 10 and 11). Necrosis, fat bodies and vacuum were found in the month of January from fishes of Nuha Aqua Farm, Manju Aqua Farm and Fish Seed Multiplication Farm, Shambhuganj ( Figures 12, 13 and 14). On the other hand, fat bodies, vacuum and necrosis were observed in the month of January from fishes of Chan Miah Fish Farm ( Figure 15). On the other hand, hemorrhage and vacuum were recorded in the month of February from fishes of Setu Hatchery and Aquaculture ( Figure 17). However, mild hemorrhage and necrosis were found in the month of February from fishes of Chan Miah Fish Farm ( Figure 16).

Histopathological observations of liver in summer season
In the liver of M. cavasius from Sharnalata Agro Fisheries Farm had identified a normal liver except vaccum in the month of March ( Figure 18). Almost normal liver were found from fishes of Reliance Aqua Farm in March ( Figure 19). Having almost normal liver were recorded in the month of April from fishes of Nuha Aqua Farm and Manju Aqua Farm (Figures 21 and 22). In the month of March from fishes of Fish Seed Multiplication Farm, Shambhuganj and Fish Seed Multiplication Farm, Maskanda necrosis (n) were observed (Figures 20 and 23).

Histopathological observations of skin and muscle in winter season
In skin and muscle of M. cavasius from Sharnalata Agro Fisheries Farm in the months of January and February there were found epidermal missing, vacuum and necrosis (Figures 24 and 25). Epidermal missing, necrosis and vacuum were also noticed from fishes of Reliance Aqua Farm, Nuha Aqua Farm and Manju Aqua Farm in the months of January and February gradually (Figures 26, 27, 28 and 29).

Histopathological observation of gill in winter season
Cyst and lamellar missing were noticed in the gill of M. cavasius from Sharnalata Agro Fisheries in January ( Figure 36). Lamellar missing and clubbing (cb) were found in fishes of Reliance Aqua Farm in the month of January (Figure 37), whereas, lamellar missing, hypertrophy and clubbing were observed particularly from fishes of Nuha Aqua Fram and Manju Aqua Farm in january (Figures 38 and 39). On the contrary, hypertrophy and missing of gill lamellae were noticed respectively from fishes of Fish Seed Multiplication Farm, Shambhuganj, Manju Aqua Farm Maskanda in the month of February (Figures 40 and 41).

DISCUSSION
Disease is a primary constraint to the growth of many aquaculture species, and is now responsible for severely impeding both economic and socio-economic development in many countries of the world. Disease problem constitute the largest single cause of economic loss in aquaculture.
From the result of the present study in January and February, 2019; Clinically, M. cavasius had deep reddish whitish lesions on the lateral side of the body in Sharnalata Agro Fisheries Farm and abrasions on the ventro-lateral side of thebody were seen Chan Miah Fish Farm Farm. Hossain (2008) mentioned that, clinical symptoms like scale loss, dermal lesions, loss of caudal fin were seen in December and January. Ahmed and Hoque (1999) also reported that clinical signs like gray white necrotic areas were increased in December, January and February invarious carp species in Bangladesh. In the months of March and April, lesions of fish were in healing stage from fishes of Nuha Aqua Farm and Fish Seed Multiplication Farm. In M. cavasius, lesions were reduced to small red patches in Setu Hatchery and Aquaculture, whereas, M. cavasius had rough skin, red spots, scale loss, weak body were seen from the farms during February and March. In the months of February and March, clinical signs of M. cavsius were still found but improved to many fold in both of the farms. Ahmed et al. (2000) mentioned that weak body, rough skin surface and mild haemorrhagic lesions were seen in catfish in February. According to Dutta (2009) in February, mild lesions, rough skin and scale loss were present in some fishes. Islam et al. (1999) and Monowara (2003) also observed that fishes were found to have been less affected during the months of March and April. The fishes of the all farms were apparently healthy and normal appearance during April. According to Ahmed et al. (2011) the investigated fishes were in healthy appearance in the months of April and May. From the research finding of Uddin et al. (2019), external organs like gill were more affected compared to internal organ like liver and fish were more affected in the months of January and February than winter season. However, all the fishes of Sharnalata Agro Fisheries Farm were clinically more affected compared to Nuha Aqua Farm in the present investigation.
From the present study, the structure of liver in all fishes had severe necrosis, vacuums and haemorrhages in all the investigated fish farms during January and February. According to Ahmed et al. Histopathologically, it was observed in the present study that in M. cavasius, epidermis and dermis were lost and muscle had fungal hyphae, fungal granuloma, haemorrhage, necrosis, melanomacrophase and vacuums in Manju Aqua Farm and epidermal and dermal missing, muscle had fungal granuloma, haemorrhage, necrosis, melano macrophase and vacuums Fish Seed Multiplication Farm in January and February. Ahmed et al. (2012) observed that in skin and muscle of Oreochromis niloticus, necrotic muscle with fungal hyphae and fungal granuloma in Bhaluka and trace of fungal granuloma were found in Muktagacha during December and January. It was found that fungal granuloma and fungal hyphae were observed in fishes of both the farms especially during December and January. The occurrence of fungal granuloma in fish organs indicated that the fishes were affected by EUS. Ahmed et al. (2007) reported that fungal granuloma in the muscle of A. testudineus from two different farms of Mymensingh district during December and January and presence of fungal granuloma in the muscle of investigated fish indicated that the fish were affected by Epizootic Ulcerative Syndrome (EUS). They also reported fungal hyphae and many granulomas in the internal organs and musculature of EUS affected Colisa lalia in Japan. In the months of February and March, epidermis, dermis and muscle were almost healed up in all fishes of both the farms. Similar findings also observed in Khatun (2011). From the research findings of Ahmed et al. (2012) it was recorded that in February, vacuums, melanocytes and protozoan cysts were found in skin and muscle of major carps. In the months of April and May almost normal skin and muscle were found in all fishes of both the farms. Similar findings also found in Ahmed et al. (2011). Thus it was observed that the skin and muscle of B. gonionotus and A. testudineus were more affected than P. hypophthalmus in December and January in the both farms.
During January and February, pathologically in gill had hypertrophy, lamellar missing, clubbing, haemorrhage, necrosis in M. cavasius of Nuha Aqua Farm and gill lamellae were hypertrophied, clubbed andlamellar missing in the fishes of Manju Aqua Farm. In case of M. cavasius, clubbing, haemorrhage, necrosis and lamellar missing were seen in Fish Seed Multiplication Farm and primary gill lamellae had hypertrophy, necrosis and secondary gill lamellae were almost lost from fishes Chan Miah Fish Farm during January and February.

CONCLUSION
Clinical and histopathological observation of Gulsha (M. cavasius) was carried out for duration of four months from January to April 2019 from the various fish farms of Mymensingh. As per clinical and histopathological observation, fish were more affected in the colder month during January and February. During March and April most of the fish were normal and healthy. Gills were the most severely affected organ followed by skin and muscle as well as liver. Major pathological changes of fish were fat bodies, necrosis, haemorrhage, vacuums, and separation of dermis from muscle, hypertrophy, lamellar missing and clubbing. More attention must be taken in winter season when environment temperature and other ecological conditions remain at unfavourable level for fish. Therefore, more precautionary measures need to be taken at the onset of winter season to prevent diseases. Further studies should be conducted on developing strategies for better health status of gulsha (M. cavasius) to prevent disease.