Abstract
A study was conducted to investigate the parasites and diseases of juvenile carps of Mymensingh region. Status of diseases and control measures taken by the farmers were observed. A total of 120 farmers were interviewed, 15 farmers from each eight Upazillas of different farm size. A total of eight (8) farms, four Government (Govt.) and four Private (Pvt.) fish farms were selected for the study. Three Indian major carps - Catla (Catla catla), Rui (Labeo rohita) and Mrigal (Cirrhinus cirrhosus) were examined during June, 2010 to May, 2012. Monthly samplings were carried out with 5 fish from each species and each farms. Altogether 2880 fish host were examined of which 1674 hosts were found to be infested with different groups of parasites during the study period. The ectoparasites were very common in gills and skin of all fishes. Eleven species of protozoan, thirteen species of monogeneans and two species of argulus were recorded. Few protozoan and monogenean could be collected for the first time in Bangladesh. Water quality parameters were taken and management practices were investigated fortnightly interval in different farms. These were almost similar for all experimental ponds. The risk of being infestation by parasites of carp significantly (p<0.001) increased when the water quality parameters such as temperature, dissolved oxygen, pH, ammonia, hardness, alkalinity, transparency and depth of water etc. were not maintained the optimum level. Diseases like ulcer, dropsey, red spot, scale protrusion, argulosis, trichodiniasis, ichthyophthiriosis, chilodonellosis, myxoboliasis, black spot, dactylogyrosis and gyrodactylosis were found very common in most of the farms. A few diseases like tumores, gas bubble and pop eye occurred only in some specific farms. Prevalence (%), mean intensity and abundance were found to be species specific and also varied with seasons and management systems practiced by different farmers. Prevalence (%) of protozoan, monogenean, argulus and all these parasites in carps was significantly (p< 0.001) higher in Pvt. farm than that of Govt. farms. The prevalence (%) of protozoan parasites in winter season was significantly (p< 0.01) higher than that of summer and rainy season. The prevalence (%) of monogenean, argulus and all parasites were significantly (p< 0.01) higher in rainy season. Mrigal was more infected by protozoan and monogenean than Catla and Rui. But Rui was more susceptible than Catla and Mrigal by argulus. For histopathological studies skin, muscle, gill, liver and kidney were collected, processed and stained in Haematoxylin and Eosin. Histologically, Indian major carps of different fish farms were more affected in colder months. Pathological changes like necrosis, fungal granuloma, protozoan and monogenean cyst, vacuolation, melanomacrophase, haemorrhage, hypertrophy, hyperplasia and clubbing were recorded in all the investigated organs. Rui and Mrigal had pathological signs like hypertrophy, hyperplasia, necrosis, haemorrhage, inflammation, vacuolation and clubbing. Similar signs were also recorded in Catla but the degrees of severity were less. Among them fish gills and skin were more affected followed by liver and kidney. In some cases, large bacterial colony and protozoan cyst were observed in the secondary gill lamellae of Mrigal. A study was also conducted to examine the effect of different common and available chemotherapeutics and doses against mixed infection of protozoa and monogenea and argulus in carps. A total of 50 parasitic infested fishes were checked before and after the treatment. Two chemotherapeutics salt (Nacl) and quick lime (CaO) were used in separate three treatments with three replication each in combination with another. Among the mean infestation percentages of mixed infection in carp after employing different dosages of lime with salt leads to the conclusion that 3rd treatment or dosage (lime + salt = 300g + 200g)/dec. was the best among the treatments under taken. One chemotherapeutics Dipterex was used in separate three treatments with three replication each. Doses of Dipterex used per decimal of water were 0.25 ppm, 0.5 ppm and 0.75 ppm for argulus infested pond treatment respectively. The higher dose (0.75 ppm/dec.) was the best as 100% recovery was recorded for Argulus infestation. Parasitic diseases start at the all stages of carps and are very susceptible to these diseases. The occurrence of diseases and parasites of Indian major carps in the surveyed habitats are species specific and related to management practices having seasonality. Present findings can be applied successfully for the prevention and control of carp diseases at farm-level.