Temporal Variations in Plankton Communities and Environmental Factors in the Shipra, a Central Himalayan Tributary of the Kosi River in Uttarakhand, India.

The essential role of smaller streams and tributaries indigenous to the area is crucial in revitalizing and restoring the main river system. The present study unraveled the relationship between plankton communities and environmental variables in the Shipra River, a Central Himalayan tributary of the Kosi River in Uttarakhand, India. Plankton distribution, abundance, and presence were investigated at four locations: upstream (S1 and S2) and downstream (S3 and S4). Forty-eight genera of phytoplankton and zooplankton have been identified belonging to ten classes (Bacillariophyceae, Chlorophyceae, Zygnematophyceae, Cyanophyceae, Euglenopyceae, Protozoa, Rotifers, Copepoda, Cladocera, and Insecta) based on the findings. Winter was dominated by phytoplankton (Navicula spp., Nitzchia spp., Diatom spp.); summer and monsoon by zooplankton (Daphnia spp., Cyclops spp., Keratella spp., Brachionus spp.). Plankton communities of the tributary were assessed using diversity indices (Shannon-Weiner's index (H), Simpson's diversity index (1-D), and Evenness Index (E)). Seasonal variations in water temperature, specific conductivity, total dissolved solids, dissolved oxygen, nitrate, and ammonium ions were found to be statistically significant (p<0.05). Canonical Correspondence Analysis, K-dominance plots, cluster analysis, and NMDS analysis showed the dynamic nature of the plankton communities with seasonal physiochemical variations in the unexplored Himalayan tributary. The plankton communities exhibited significant temporal fluctuations with physicochemical factors.

Clinical signs, lethal dose and histopathological lesions in grass carp, Ctenopharyngodon idella experimentally infected with Edwardsiella tarda.

An experiment was conducted to study the lethal dose (LD50-96h) and histopathological changes occurring in several organs of grass carp challenged with different concentrations of Edwardsiella tarda. The healthy grass carps were challenged with the bacterial suspension of 106,107, 108, 109 and 1010 CFU ml-1. The study demonstrated that the lethal dose (LD50-96h) of E. tarda for grass carp is 1.3 × 109 CFU ml-1. The infected fish showed abnormal swimming behavior, slower movements, skin necrosis, hemorrhages, and open lesion on the fontanelle of the frontal bone of the skull during the initial phase of infection. About 60% of the fish which received the bacterial suspension of 1010 CFU ml-1 died within 24 h of infection. The histopathological examination of the infected tissue section demonstrated the severe damages in the internal organs. In gills, oedema, secondary lamellae fusion, and hyperplasia of basal epithelial lining between secondary lamellae were reported. The microscopic observation showed the disruption of submucosa to the mucosa, which finally led to degenerative changes in the intestine, necrosis of hepatocytes and infiltration of red blood cells in the liver. The tubular disintegration in kidney and loss of capsular boundary of red pulp in spleen were also reported. In conclusion, the result indicates that the infection caused by E. tarda can cause severe damages and alterations in grass carp tissues and potential mass mortality. Moreover, The bacteria isolated from the mobribund fish was characterized by biochemical tests and expression of five critical virulence genes like citC, fimA, gadB, mukF and gyrB were detected from the microorganism. The study aims to provide a research foundation for further studies on the susceptibility and pathological changes of grass carp induced by E. tarda infection.