Abstract
A study was conducted to investigate the impact of seasonal variation of water quality parameters, parasitic
infestations, bacterial loads and clinical and histopathological observations of six endangered open water fishes
from the months of June 2014 to May 2016. Water quality parameters like temperature, dissolved oxygen, pH,
alkalinity, hardness, ammonia and nitrite values were recorded and fish samples were collected from Kailla
beel, Ishoregonj, Mymensingh, Kangsa river near Jaria, Netrakona, Noli beel, Kapasia, Gazipur and Surma
river, near Gobindaganj, Chatak, Sunamganj at monthly intervals. Temperature, alkalinity and hardness
were significantly (p<0.05) reduced and ammonia and nitrite values were increased significantly (p<0.05)
during winter season in the both years which were unfavorable for fishes. However, in other seasons more or
less similar results were found in the investigated water bodies. The highest bacterial loads (p<0.05) in fish
liver were recorded in Macrognathus aculeatus (6.84 x 109 cfu/g) followed by Lepidocephalichthys guntea, Botia
dario, Glossogobius giuris, Colisa fasciata and Monopterus cuchia. The highest bacterial loads (p<0.05) of kidney
were in M. aculeatus (5.87 x 109 cfu/g) followed by by L. guntea, B. dario, G. giuris, C. fasciata and M. cuchia. The
highest bacterial loads both in fishes and water were found in Kailla beel followed by Noli beel, Kongsa river and
Surma river throughout the experimental period. The highest (p<0.01) bacterial loads in fishes and water were
found during winter season and minimum was recorded during summer season. Bacterial loads in fishes and
water were not significantly different in rainy and autumn seasons. Maximum prevalence, mean intensity and
abundance of parasites were the highest (p<0.01) in winter season followed by rainy, autumn and summer
seasons. The highest (p<0.01) prevalence, mean intensity and abundance of parasites were found in fishes of
Kailla beel (58.83%, 2.05 and 1.21) followed by Kongsa river, Surma river and fishes of Noli beel. Fishes were highly
(p<0.01) infested by digenetic trematode followed by monogenetic trematode, protozoan, cestode,
acenthocephala and nematode. However, the highest (p<0.05) prevalence, mean intensity and abundance of
parasites was found in G. giuris (100%, 2.00 and 1.40) followed by M. aculeatus, L. guntea, B. dario, M. cuchia and
C. fasciata. Clinically, it was observed that fishes of investigated water bodies had less pathological signs in
autumn, slightly increased in rainy and late autumn and more pathologies during winter season. However,
fishes had recovered to almost normal appearance in summer. Clinically fishes of Kailla beel was most
affected followed by Kongsa river, Surma river and Noli beel. The M. aculeatus, was highly affected
followed by L. guntea, G. giuris, B. dario, M. cuchia and C. fasciata. The diseases recorded from investigated
water bodies were epizootic ulcerative syndrom, ichthyophthiriasis, trichodiniasis, chilodoneliasis,
myxoboliasis, dactylogyrosis, gyrodactylosis, branchiomysis, red spots disease, tail and fins rot, gill rot, eye and
anal protrusion, bone deformities and dropsy throughout the study. Histopathologically less pathological
signs were observed in autumn and which was gradually increased during rainy and late autumn
seasons. The highest pathological changes were observed during winter and in summer pathological signs of fishes were gradually healed upto almost normal condition except few vaccums and hemorrhage in
internal organs. Most of the examined fishes were normal and healthy from external observations but
histopathologically a great number of fishes were affected with various pathological changes especially
during winter season. However, histologically fishes of Kailla beel was the most affected followed by
Kongsa river, Surma river and fishes of Noli beel. M. aculeatus was highly affected species followed by L.
guntea, G. giuris, B. dario, M. cuchia and C. fasciata. Winter was the most affected season followed by rainy,
late autumn, autumn and summer seasons. However, incidence of disease outbreak of fresh water fishes
of Bangladesh might be related to seasonal variations and environmental factors. Thus it could be
mentioned that, proper management techniques should be taken especially in winter season for open
water fishery in order to save these important fishes from further reduction and extinction.