The spread of Covid-19 has reduced human intervention in aquatic ecosystems, which has shown a discernible improvement in air and water quality. Ganges River, being a historical, economic and cultural icon of India providing multiple ecosystem services as industrial, provisioning, regulatory and cultural services, constitutes an important habitat for Gangetic Dolphin (Platanista gangetica). The surfacing of dolphins in Ganga river is patchy and unpredictable. The present study unravels 25 different chemical, microbiological, biological and meta-genomics of most abundant bacteria at dolphin surfacing sites in Ganges water during October 2017 February 2018 and January 2021 to elicit the impact of Covid-19 lock down at the Garhmukteshwar (28.7601°N, 78.1437°E) stretch in Hapur district of Uttar Pradesh, India. The most abundant bacteria at dolphin surfacing site was Bacillus subtilis in February 2018 which was replaced by Aeromonas sp. in January 2021. The zooplankton community was dominated by rotifers during pre-Covid period however the dominance pattern recorded a shift towards larger herbivorous crustacean species during Covid -19 lock down. Overall bacterial count decreased whereas Chl a level increased during the lock down. The total zooplankton abundance did not show a significant difference, but relative proportion of larger herbivorous crustacean zooplankton increased in January 2021 samples. The present results convincingly establish effects of shutdown on chemical, metagenomics and biological components of the riparian ecosystem and the information of micro to mesoplanktonic community may be useful for characterizing dolphin surfacing sites, enhancing existing water quality monitoring efforts and also for human epidemiological studies associated with recreational use of Ganga water.

The advent of the 2019 Corona virus impacted day-to day human activities and the nationwide lockdown in India completely paralyzed life (midnight of 24^th March, to 31^st June, 2020). However, this complete halt of human activity allowed the Ganga ecosystem to realise its maximum self-purification potential, resulting in the improvement of flow regime, water quality and over all restoration of the river. The most common manifestation of restoration of an aquatic ecosystem is zooplankton community structure; i.e. relative proportion of various functional feeding groups. The present study compares selected water quality parameters (DO, BOD, pH, Total coliform, Fecal coliform), and zooplankton community structure estimated during the lockdown period with the values recorded for the same period in previous three years at dolphin appearing site near Kalighat, (25° 37′ 19.398″ N; 85° 9′ 55.8972″ E), middle of the Patna city and Mittal Ghat (downstream site of the Patna City) at Gurhatta (25° 36′24.5772″ N; 85° 13′ 1.6788″ E). During each sampling, the dolphin emergence site and frequency were monitored for three hours duration. Monthly zooplankton samples were collected at both the sites using a 53 µm mesh size plankton net beginning January 2018 by filtering 45-50 l of river water. Zooplankton were identified and segregated based on functional feeding groups. The values of dissolved oxygen were significantly higher, whereas that of BOD level, total coliform and total fecal coliform were lower during the lockdown period than those in previous years. Detailed analyses revealed that relative proportions of Cladocera were significantly higher, whereas that of bacterivorous Rotifera were significantly lower than the previous values of the same months. The highly indicator species at both the sampling sites was Moina micrura during March-May 2020; in previous years it was Brachionus rotifers 8.8 (ind l^-1) at Kalighat and Moina micrura (15 ind l^-1) at Gurhatta. Our results suggest that during the lockdown the dolphin appearing sites at both stations shifted towards the riverbank whereas, zooplankton community structure changed towards algaevorous Cladocera without affecting overall species richness.

Nepal is a land-linked country relatively small in area. However, it is home to several rivers, and these rivers are undoubtedly beautiful additions to the mountainous nation's splendid scenic landscape. Most of Nepal's surface water drains through the three major rivers are Saptakoshi, Narayani, and Karnali. Mechi and Mahakali Rivers and their tributaries mark the international boundaries between Nepal and India. All of these originate either from the Himalayas or from the Tibet Plateau and are perennial. However, dams and other water development projects, intensive fishing, pollution, and extensive human disturbances have decreased the abundance of the Ganges River Dolphin, which is now restricted only to the Koshi and Karnali River systems and in an isolated form. The first Integrated Dolphin Census of Nepal, conducted in 2016, recorded 52 dolphins throughout the country. Of the 52 dolphins, 43 were sighted in the Mohana of Karnali and its tributaries. No dolphins have been recorded recently for the Mahakali river, and sightings in the Narayani river, are occasional. The population of the River Dolphins is declining at an alarming rate. Therefore, it is important to regularly assess the status and trends of their populations and design strategies for their conservation and sustainable use.

Nepal is endowed with vast water resources in form of glaciers, lakes, streams and rivers. All the rivers in Nepal are connected to the Ganges River system of India. The major rivers are reliable sources of water and provide habitats for aquatic animals, opportunities for hydropower, and irrigation development in downstream regions. The major rivers of Nepal include the Koshi, Gandaki (Narayani), Karnali, and Mahakali which all drain from north to south. These rivers support abundant wildlife species as well as a number of fishes, amphibians and reptiles. Most relevant to this paper is the Ganges River Dolphin (Platanista gangetica gangetica Roxburgh, 1801). The Ganges River Dolphin preys on fish, mollusks and other aquatic animals. Being a migratory species, the dolphins move from larger rivers to their tributaries, seasonally. This paper is intended to review work on the status of Ganges River Dolphin in Nepalese rivers based on secondary data obtained from different published surveys targeting the dolphin populations. The records show the Karnali River has the largest population, followed by the Koshi and Narayani rivers, with no record of dolphins occupying the Mahakali River in recent years. Recent surveys estimate about 100 dolphins living in Nepal, with 80 estimated in the Karnali River. Different anthropogenic activities including construction work, intensive fishing, pollution and the lack of conservation planning for dolphins have resulted in a decline in number from historic levels. The presence of this aquatic mammal is considered as an indicator of the overall health of the river system. The COVID-19 pandemic and lock down might have caused increased dolphin sightings. Additionally, high pre-monsoon precipitation in recent years have caused higher water levels in smaller rivers, possibly causing the dolphins to return earlier than usual to the major river systems. They were recorded to be present in the Mohana and other small tributaries of the Karnali River as early as first week of June.

The Gangetic Dolphin (Platanista gangetica) was once found in tens of thousands in the rivers of the Indian sub-continent, but the numbers have now dwindled abysmally throughout its geographical distribution. In northeastern India too, dolphins were seen in all the major rivers and also in certain wetlands during monsoon months till the early 1980s. However, the sighting of dolphins is rare now due to natural and human-induced factors. Three factors - adequate water cover, water quality, and abundance of prey food either individually or in combination- relate to River Dolphins' existence. Variability of meteorological parameters also severely impacts on the limno-biological parameters of riverine habitats. Restoration of Gangetic Dolphins in their traditional habitats can boost ecotourism in the region. An extensive study is necessary to assess the cumulative impact of the proposed hydroelectric projects on the aquatic biodiversity of the entire eastern Himalayan region. The need of the hour is to adopt a holistic and participatory approach for maintaining riverine health and the prey base of the Barak and the Brahmaputra systems.

The Ganges Dolphin needs uninterrupted water sources in order to both communicate and to locate its food. Ever-increasing activities in the rivers, especially from motorized vessels, are likely to add noise to the soundscape used by this animal and may affect its ability to locate its prey or to sense its environment. Although efforts have been made to improve the quality and flow of the water passing through the Ganga River system, a coordinated effort among policymakers, local implementing authorities, researchers, and funding agencies is needed to achieve the desired goal of restoring the habitat of dolphins, stopping their accidental deaths, increasing their number by captive breeding, and reinstating the biodiversity of aquatic organisms that are passively or actively linked to them. While passive restoration plans such as improving water quality, increasing water volume, and habitat reclamation may work well, the developmental needs along the river exert constant pressure on these plans. These plans may not be effective without the strict enforcement of guidelines, an understanding of the requirements of the plans by all the stakeholders, and the awareness of the population living along the rivers. Therefore, conservation efforts, along with ongoing passive restoration processes aimed at improving the dolphin's living ecosystem by providing enough quality water cover and prey, should focus on increasing the population of these animals by propagating them in captivity through biological or biotechnological means, the success of which needs strong scientific research backing. A scientometric analysis of 20 years (2001–2020) on this animal shows that scientific studies are confined to the ecology of the animals and very little is known either of their biology or their genetics. During the study period, India occupied fourth spot in number of publications on river dolphins, with the Indian Institute of Technology as leading institute. Advance biology techniques may allow us to breed the animal in captivity and even clone the animal. However, the research towards this requires creating the necessary basic infrastructure, funding, and policy support, and developing human resources for research and management.

Organophosphates and synthetic pyrethroid pesticides are used in residential areas and agriculture, discharge into environment, may cause unpredictable toxicity to non-targeted aquatic organisms. The current study aims to assess the effect of these pesticides on the transaminases, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase enzymes activity in brain and gills of Oreochromis niloticus. Fish were exposed for 24 and 48 h (hours) to the LC₀ (non-lethal concentrations) of the malathion, chlorpyrifos and λ-cyhalothrin, respectively. For biochemical assay, a spectrophotometer was used. Glutamate oxaloacetate transaminase activity in brain and gill was significantly (p<0.05) elevated and inhibited, respectively, except in 48 h treated samples. The highest (+258%) and lowest (+8.9%) enhancement in this activity was noted in chlorpyrifos and malathion treated gill samples, respectively. The glutamate pyruvate transaminase activity was significantly (p<0.05) enhanced in all treated samples except in 24 h malathion treated brain. The highest (+340.7%) and lowest (+27%) enhancement in this level was recorded in malathion and chlorpyrifos exposed brain and gills samples. Therefore, it is suggested that both these assessments in fish different organs could be used as a useful biomarker to detect environmental pollution. Thus, the alterations in transaminases activity indicated that the tested pesticides are highly toxic to the health of aquatic organisms and should be periodically and regularly monitored in the environment to reduce pollutant stress on non-target biota, particularly fish.

Dam removal is a potential habitat restoration alternative through which parties responsible for injuries to natural resources can provide compensation for reductions in fish populations. Predicting the potential response of migratory fish populations to candidate dam removal(s) is a critical step in the natural resource damage assessment process to evaluate whether the proposed action provides adequate compensation. There is currently no standard approach to making such predictions, particularly in cases where data on candidate streams with dams are limited. We considered six modeling approaches for addressing this problem and evaluated the features of each approach for this application. We judged that an approach based on habitat suitability indices and weighted usable area provides the best balance between predictive capacity and cost of model implementation. This balancing act evaluating the cost effectiveness of predictive models is worth consideration in a wide range of fisheries modeling applications.