Abstract
Studies on the etiopathology and control measures of ulcer diseases in the cultured fishes were conducted in Mymensingh and surrounding six districts (Kishorganj, Netrokona, Sherpur, Jamalpur, Tangail and Gazipur) during the period from October 2001 to March 2003. The diseases were found to occur in some fishes of the investigated water bodies with high prevalence during the winter months, especially in January and February. Out of 11 fish species, Cirrhinus cirrhosus and Barbodes gonionotus were found to be severely affected by the disease. Six species viz., Barbodes gonionotus, Catla catla, Cirrhinus cirrhosus, Labeo gonius, Labeo rohita and Morulius calbasu were histopathologically diagnosed as EUS- positive and four species viz., Cyprinus. carpio Com., Ctenophyrongodon idellus, Hypophthalmichthys molitrix and Pangasius hypophthalmus were detected as EUS-negative (Non-EUS). A total of 31,540 (18.78%) fish were found to be affected of which 11.98% were EUS-positive and 6.80% were EUS-negative. In total, 355 bacterial isolates were recovered from the ulcer-affected fish including EUS. The recovered suspected bacterial pathogens (Aeromonas, Pseudomonas and Edwardsiella) were identified up to species level. Among the Aeromonas isolates, 79 A. hydrophila, 31 A. veronii biovar sobria, 24 A. veronii biovar veronii, 16 A. schubertii, 10 A. jandaei and 80 Aeromonas spp. were found. In case of Pseudomonas, 50 isolates were identified as P. fluorescens and 33 isolates of Edwardsiella were identified as E. tarda. The highest number of aeromonad and Pseudomonad isolates were recovered from C. cirrhosus followed by B. gonionotus. E. tarda were found to be prevalent in P. hypophthalmus.
In pathogenicity test, most of the suspected pathogens were found to be pathogenic in injection method. A. hydrophila was found to be more pathogenic than the other isolates. In virulence study, all of the bacterial isolates tested were found capable of producing infection with the exposure dose of 3.5x10° CFU/ml bacteria. The isolate A. hydrophila Ah-11 was found to be significantly (p<0.01) virulent. In case of 7 experimental water, percentage of infection was observed to be significantly (p<0.01) high in pond water followed by lake water. No infection was detected in salt + lime water.
A total of 74 fungal isolates were recovered from fungal affected fish (including EUS) and primarily identified as Aphanomyces, Saprolegnia and Achlya. Of the 40 isolates of