Marking World Fisheries Day (WFD) 2025, we present some of important studies and reports highlighting the growing threats over freshwater fish species in India and across the globe. The multi-taxon global freshwater fauna assessment for The IUCN Red List of Threatened Species published this year is among most concerning report revealing looming extinction threats over 24% of freshwater fauna worldwide. This includes the hump-backed mahseer, subterranean snakehead and peninsular hill trout found in rivers and waterbodies of Western Ghats.
Another study has estimated India fishery sector losing over $2 billion annually due to water pollution. The sector is facing sustainability challenge on several fronts addressing which requires a multifaceted approach. At the same time the critical gaps in research and policy have impacted freshwater megafauna in India where focus is largely on the mega fish and other aquatic animals are understudied. The year has seen informative studies on freshwater eco-system in Loktak and Ashtamudi lakes. There are also research and reports emphasizing on the growing destruction of fish habitats and diversity by indiscriminate riverbed mining in Godavari, Ganges and Indus basin. We have also in separate overviews covering important developments concerning fisheries sector in India and impact of dams on inland fish and fishers in the country.
1 One-quarter of freshwater fauna threatened with extinction Abstract Here we present the results of a multi-taxon global freshwater fauna assessment for The IUCN Red List of Threatened Species covering 23,496 decapod crustaceans, fishes and odonates, finding that one-quarter are threatened with extinction. Prevalent threats include pollution, dams and water extraction, agriculture and invasive species, with overharvesting also driving extinctions. We also examined the degree of surrogacy of both threatened tetrapods and freshwater abiotic factors (water stress and nitrogen) for threatened freshwater species.
Threatened tetrapods are good surrogates when prioritizing sites to maximize rarity-weighted richness, but poorer when prioritizing based on the most range-restricted species. However, they are much better surrogates than abiotic factors, which perform worse than random. Thus, although global priority regions identified for tetrapod conservation are broadly reflective of those for freshwater faunas, given differences in key threats and habitats, meeting the needs of tetrapods cannot be assumed sufficient to conserve freshwater species at local scales.
4 in 10 species inhabiting inland water ecosystems in the Western Ghats face the threat of extinction, conservation scientists said on Jan 8, 2025 after a worldwide assessment covering habitats critical to livelihoods & environment. The assessment by an international consortium of researchers has estimated that 24% of freshwater fauna worldwide are threatened with extinction, with at least 4,294 of the 23,496 freshwater animals at high risk of extinction.
Among the Western Ghats’ threatened species are the hump-backed mahseer found only in the River Cauvery, the subterranean groundwater dragon snakehead fish, and the peninsular hill trout, found only in the River Periyar. In the Western Ghats, growing populations of non-native fish such as the African catfish, common carp, or tilapia too pose a threat to native fish, Rajeev Raghavan, assistant professor at the Kerala University of Fisheries and Ocean Studies, Kochi, and a study co-author said.
The study found that among the groups studied, 30 per cent of crabs, crayfishes and shrimps are at risk of extinction, followed by 26 per cent of freshwater fishes and 16 per cent of dragonflies and damselflies. Of the freshwater species under threat, 54 per cent are threatened by pollution, 39 per cent by dams and water extraction, 37 per cent by agriculture and other land use changes, and 28 % by invasive species and diseases. The study led by IUCN and published in the multidisciplinary science journal, Nature, underscores the historical underappreciation of freshwater ecosystems in global environmental governance.
On the basis of monitored natural inland wetlands (including peatlands, marshes, swamps, lakes, rivers, and pools, among others), 35% of wetland area was lost between 1970 and 2015, at a rate three times faster than that of forests… Of the remaining wetland habitats, 65% are under moderate-to-high levels of threat, and 37% of rivers over 1,000 km are no longer free-flowing over their full length. Declines are continuing, generally out of sight and out of mind, despite the importance of the freshwater realm. Freshwaters support over 10% of all known species, including approximately one-third of vertebrates and one-half of fishes, while only covering less than 1% of the surface of the Earth.”
Nowhere is this loss more profound than in the Western Ghats, a freshwater biodiversity hotspot and home to many endemic species. The study identifies this region as one where freshwater species are most threatened. “There are over 300 species of freshwater fish in the Western Ghats. More than half of them is found only here and nowhere else on Earth, making them exceptionally vulnerable to environmental threats,” said Dr Rajeev Raghavan, assistant professor at the Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi. According to him, Kerala has the highest number of threatened freshwater fishes in India (74), and the Periyar River is the most significant in terms of ‘conservation attention’ as it harbours the maximum number of endemic & threatened freshwater fishes in Kerala. This first ever global assessment of freshwater animals has found that one quarter of the 23,496 freshwater species surveyed by the IUCN Red List of Threatened Species™ are under the threat of extinction. Western Ghats in India are one of the top hotspots showing the greatest threat.
2 India’s fishery sector loses $2.2 bn annually due to water pollution India’s fishery sector loses over $2 billion due to untreated wastewater contaminating waterways, according to a study published on Apr 23. Launched at the World Ocean Summit in Japan by ocean health initiative Back to Blue and the Ocean Sewage Alliance, the study highlights the high cost of inaction in wastewater management in Brazil, India, Kenya, the Philippines and the United Kingdom. Since India is a major seafood supplier, this threatens both domestic food security and export markets. Also, among the countries studied, India incurs the highest healthcare costs from diarrhoea linked to contaminated drinking water. With a wastewater treatment rate of just 21%, nearly three times as many people are affected, with annual cost of $246 million.
India experiences lower proportional losses due to lower soil salinity but still suffers the highest absolute revenue loss ($1.2 billion), the study says. Around 10% of agricultural land in developing countries is irrigated with raw or partially treated wastewater, which often contains toxic heavy metals like zinc, chromium, manganese and iron. While wastewater nutrients such as nitrogen and phosphorus can initially boost crop yields, long-term use leads to soil salinisation and reduced yields.
Policymakers who look beyond infrastructure investment and focus on circularity can ensure wastewater is repurposed as organic fertiliser, biogas or even a source of renewable energy, Wenger added. Like much of the developing world, India views wastewater pollution partly through the lens of water scarcity. Asserting that expanding treatment capacity is key, Nitin Bassi, senior program lead for sustainable water at the CEEW said, “We need to improve both water quality and the usable quantity of water. If more wastewater can be captured, treated, and reused, it will reduce the pressure on our freshwater resources.
3 Fisheries & aquaculture in India: Past, present & future Abstract Currently, the Indian fisheries sector, contributing to rural livelihoods and food security, including eliminating hidden hunger, reflects a blend of traditional practices and modern innovations. However, several sustainability challenges exist, including overfishing, habitat degradation, climate change, disease outbreaks, and socioeconomic vulnerability of fishing communities. Addressing these, and moving towards resilient, inclusive, and sustainable aquatic food production systems will require a multifaceted approach integrating policy reforms, ecosystem-based management, technological innovation, and community participation—all of them aligning with the Sustainable Development Goals & FAO Blue Transformation strategy.
4 Conservation of India’s freshwater megafauna Highlights First study to assess India’s freshwater megafauna (IFM) as a collective. Text mining reveals research-policy misalignment in IFM conservation. Mega-fishes dominate research but lack policy attention; mammals/ reptiles are understudied. Critical gaps exist in climate change, hydrology, and habitat fragmentation research. Findings offer globally relevant insights for IFM conservation.
5 Study links land use to water pollution in Loktak Lake A Nagaland University study has flagged an environmental worry for Manipur’s Loktak Lake, a freshwater ecosystem distinguished by its floating biomass called phumdi in the Meitei language. Loktak Lake is home to 132 plant species and 428 animal species, and supports hydropower, fisheries, transport, and tourism. The lake features in the Montreux Record, a global warning list for wetlands undergoing serious ecological damage.
The findings pointed out that changes in land use – agriculture, settlements, and shifting cultivation – have been deteriorating the water quality of rivers feeding the lake, threatening its biodiversity and the livelihoods of the local communities. To understand the root cause of water pollution in the lake’s catchment area, the researcher conducted field samplings across nine major rivers that drain into Loktak. These rivers are Khuga, Western, Nambul, Imphal, Kongba, Iril, Thoubal, Heirok, and Sekmai.
The Nambul River was identified as the most polluted, with low oxygen levels and high organic contamination linked to 47% of the agricultural land, and 11% of the settlement areas in its sub-catchment. The Khuga River showed the second poorest water quality, despite having a higher forest cover. The researcher attributed this to extensive jhum, which was recorded at 42% in the region. In contrast, rivers including Iril and Thoubal, which flowed through greater forest-dominated landscapes, displayed better water quality, highlighting the protective role of natural vegetation.
Reduced fish populations, rising pollution levels and increased sedimentation have now become growing concerns. The study highlights the pressing environmental challenges arising from agricultural runoff, human settlements, and shifting cultivation, which are directly impacting the river water quality in the region.
6 Gobioid fishes of Ashtamudi Ramsar Lake Abstract An integrative taxonomic study on the gobioid fishes of Ashtamudi Lake (a Ramsar Site), Kerala, India revealed the occurrence of 12 species representing 10 genera, including three species of the genus Oxyurichthys. The Arrowfin goby, Oxyurichthys tentacularis, considered as the mainstay of gobioid fisheries in the Lake for over 40 years, represents a clear case of misidentification of O. ophthalmonema. Combined morpho-molecular analysis confirmed, for the first time, the occurrence of Oxyurichthys omanensis in the Indian subcontinent, and from anywhere outside its type locality in the Gulf of Oman.
Three additional new records are presented: Exyrias puntang from mainland India, Paratrypauchen microcephalus from the West coast of India, and Istigobius diadema from the southwest coast of India. Intensive region-wise studies, particularly along the west coast of India, are required to better understand the diversity and distribution of estuarine and freshwater gobies.
For the past 40 years, the Arrowfin Goby was identified as the main species of Ashtamudi Lake. It was first mentioned in the literature on fishes of Ashtamudi in the early 1980s. Due to the significant commercial interest in the Arrowfin Goby, several studies were conducted to determine its key life history and biological characteristics but not much was done to confirm its identity. Arrowfin Goby is a marine fish found in Indo-West Pacific waters and does not survive in freshwaters. What was thought to be the Arrowfin Goby is actually the Eyebrow Goby. As the identification and naming were incorrect, the fishery management was also not conducive to the fishery.
The findings come at a crucial time as Ashtamudi Lake faces increasing ecological stress and anthropogenic pressures. The research team emphasises the importance of a comprehensive management strategy tailored to the multispecies Oxyurichthys fishery, which sustains traditional fishers and meets a growing culinary demand. “Incorporating genetic tools in fishery assessments will be essential for identifying overexploited stocks and implementing conservation-oriented, species-specific management policies,” said Prof A Biju Kumar, Kerala University. This discovery uses both traditional and molecular techniques; has significant implications for conservation and sustainable management of this exploited fishery.
7 Telangana fish diversity at risk from sand mining & pollution: ZSI Telangana’s fish diversity, the highest among states in the Godavari River basin, is under significant threat due to sand mining, pollution, deforestation, and unscientific fishing practices, according to a survey by the Zoological Survey of India (ZSI). The ZSI survey identified sand mining as a major threat to breeding grounds of game fish species such as Labeo fimbriatus, Tor khudree, Pangasius pangasius, and Silonia childreni. These species rely on small streams and tributaries for spawning, but mining activities destroyed these habitats, leading to a sharp population decline, particularly in the upper Godavari region. Similarly, pollution from untreated sewage in cities like Nasik, Nanded, and Kopargaon and waste from paper industries in Bhadrachalam severely affected aquatic environment.
– The study on fishes particularly in Godavari river emphasized the need for immediate conservation efforts. Experts recommend the establishment of fish sanctuaries along critical stretches of Godavari, such as downstream of the Gangapur and Vishnupuri dams, Nanded, and its confluences. The study also warned of the impact of climate change on fish habitats, including reduced water flow during dry seasons and habitat loss due to variability in rainfall patterns.
8 River ecosystems in the shadow of sand mining -Continuous removal of a sand layer of the riverbed can lead to the destruction of the habitat of microorganisms maintaining the river’s biological health and endanger ecosystem services. Increased turbidity due to sand mining in active channels can block sunlight, hinder photosynthesis, and exterminate aquatic life like diatoms, macroinvertebrates, benthic algae, and fish eggs.
-The shallow and braided flow impedes fish migration between flows and pools, disrupting the entire food web. Studies show that rampant sand mining has threatened species like the Ganges River dolphin and Chambal River’s gharial. Further, unregulated sand mining results in the loss of aquatic flora and also riverside vegetation due to lowered water table, damaging the ‘Shaded Riverine Aquatic Habitat’ (SRA), which provides shade, bank stabilization, and nutrients to numerous organisms. (BKP Sinha and Ajay Jha former PCCFs UP & Maharashtra)
9 J&K: Unchecked mining causes irreparable damage to Jhelum The illegal removal of sand further aggravates the situation by deepening the riverbed, causing water levels to drop even further. The impact of the unabated sand mining has also affected severely the ecosystem of this waterbody. The Jehlum supports a diverse range of fish species and other aquatic organisms. The destruction of riverbeds due to sand mining disrupts breeding and feeding grounds, impacting local fisheries and the livelihoods dependent on them.
Mining, climate change affecting native fish One main anthropogenic factor affecting Nallah-e-Mawer is illegal sand mining from the river for two decades, which continues even now with hand tools. This activity disrupts the natural migratory path of fish that move from lower to the upper stretches of the stream. “Fish rely on biological and chemical habitats for survival, and their migration is possible only when there is an adequate water supply,” said Aatif Qayoom, a prominent environmental journalist in Kupwara. But it’s climate change that has so far had the most insidious effect on the native fish population.
10 Dredging may not solve charru mussel invasion in Ennore-Pulicat wetlands The unchecked spread of charru mussels (Mytella strigata) across the Ennore-Pulicat wetland system continues to raise concern, as govt agencies remain without a clear or sustainable plan to contain the invasive species. Field surveys conducted by the National Centre for Sustainable Coastal Management (NCSCM) in May 2025 revealed that mussels had colonised multiple pockets along the 24-km stretch from Ennore Creek to Pulicat Lake.
In response to long-standing complaints from fishermen, dredging was initiated in some sections of the creek. A 1,700-metre stretch at Kattupalli and another 500 metres at Puzhuthivakkam were taken up by the Water Resources Department, at an estimated cost of ₹20.85 crore. However, the NCSCM, in its recent submission to the NGT, has warned that both manual and mechanical dredging pose serious ecological risks. These include habitat destruction, disruption of sediment layers, loss of native aquatic species, and long-term degradation of water quality.
With no clear removal method and the final NCSCM report still pending, the fishermen are a worried lot. While dredging, despite its potential environmental impact, is still seen as useful by Mr. Kumaresan, he acknowledges that it is not a permanent solution, as the mussels could return. However, the dredging is being carried out unevenly, making it difficult for fishermen to navigate their boats through the affected areas. A value-addition study is underway to explore possible commercial uses for the mussels, such as in animal feed or fertiliser. However, the study remains incomplete and cannot yet support a full-scale removal strategy.
Some More Relevant Studies
Nepal: Hurdles & opportunities for conservation of native fish biodiversity Abstract A steep north–south elevational gradient in Nepal supports a diverse freshwater fish fauna ranging from cold water to tropical species. About 23% of the land area of Nepal is protected, but the conservation of water resources and aquatic species, which provides critical ecosystem services, has yet to be a primary goal. Threats to native fishes include habitat alteration, nonnative species, dams, unregulated exploitation & climate change. Additionally, the fishes of Nepal are under sampled and inadequately known, with high levels of taxonomic uncertainty, potential cryptic species, and species that are likely unknown to science.
Opportunities for effective conservation of native fish biodiversity are emerging, however, and center on the co-production of knowledge and co-development of conservation strategies with local communities. A multifaceted approach that integrates conservation with sustainable development is needed to protect Nepal’s unique ichthyofauna and to promote a sustainable future for aquatic resources that are crucial to Nepal’s ecology, economy, and culture.
Asia: Scientists raise red flag while studying fish The presence of polystyrene microplastics in one of Asia’s most important species of freshwater fish can cause severe complications in its overall health. In a study published in the journal Agricultural and Biological Sciences, a team of researchers revealed that the development of the Labeo rohita, or Rohu, can be greatly impacted by microplastic pollution.
-According to the research, Rohu fingerlings that were given food with 2.5% polystyrene microplastic contamination saw a “notable decline in growth and feed consumption.” While taking a closer look with a microscopic inspection, researchers found that the gut of these fish revealed “significant abnormalities in their intestines, including villi structure disruption and increased mucus cell proliferation.” As a result, the researchers concluded that “long-term polystyrene microplastic exposure may compromise fish well-being and nutritional uptake.”
-The Rohu fish is a very important fish in many Asian countries due to its nutritional value, economic significance, and cultural relevance. As noted by the polystyrene microplastic exposure in the Rohu, microplastic pollution can have detrimental impacts on the food chain. This can disrupt vulnerable ecosystems and ultimately harm biodiversity.
Europe: Overlooked impacts of freshwater scarcity on oceans Abstract This study reveals the consequences of decreased freshwater flow on marine ecosystems in the Mediterranean Sea due to climate change and escalating water demands. A 41% reduction in river flow may result in a 10% decline in marine primary productivity and a 6% decrease in biomass of commercial fish and invertebrate species. Regional reductions could be as high as 12% and 35%, disrupting coastal and marine ecosystems and their related socio-economic sectors. The findings emphasize the importance of considering nutrient load changes in water management strategies and incorporating marine ecosystem requirements into environmental flow requirements for freshwater bodies. Integrated, source-to-sink management approaches are crucial for sustainable water resource utilization.
The low water in Europe’s rivers flowing into the Mediterranean would cause a ‘profound alteration’ of coastal ecosystems due to reduced freshwater and nutrients inputs that lead to a decrease in primary productivity of the system. This, in turn, would affect the whole food chain and ultimately impact the commercially exploited seafood species.
Brazil: Human land use & non-native fish species erode ecosystem services Abstract Combining 21 years of fish size spectrum data and fishery potential (fishery monetary value in the Upper Paraná River Floodplain, Brazil), we demonstrate that the size spectrum exponent of native species has become more negative over time, indicating a relative decrease in the biomass of large versus small individuals. Conversely, the size spectrum exponent of non-native species has become less negative over time owing to the increased abundance of large species. Overall, fishery potential declined by more than 50% over time. Human land use replaced the coverage of natural environments, indirectly reducing native richness. This scenario decreased the exponent of the native size spectrum, indirectly reducing fishery potential. Our study illustrates how intensification of human land use alters the size structure of communities, favouring non-native individuals and suppressing ecosystem services.
US: Riverine Heat Waves New research shows that riverine heat waves – periods of abnormally highwater temperatures in rivers – are becoming more common, more intense and longer-lasting than they were 40 years ago. Their frequency, intensity and duration are also increasing at rates more than twice as fast as heat waves in the atmosphere. The increased heat puts more stress on aquatic ecosystems, water quality, energy production and agriculture, and it can threaten species that rely on cool streams. Riverine heat waves are disruptive in ways that can cascade through aquatic ecosystems.
Cold-water fish such as trout and salmon are especially vulnerable: Extended periods of abnormally highwater temperatures can impair reproduction, slow growth and trigger mass die-offs. Warmer water also holds less oxygen, potentially suffocating aquatic life. In addition, hot water increases the likelihood of algae blooms and elevates the cost of treating water to make it safe for drinking. Warmer water can also create problems for energy production. Many thermoelectric fossil fuel plants and nuclear plants depend on river water for cooling, and warmer water reduces energy production efficiency, which could mean higher power costs.
Despite these serious risks, riverine heat waves have gone quietly unnoticed. That’s due, in part, to the narrow width of rivers and streams. Measuring the temperatures in narrow, winding streams requires high resolution that many satellite sensors lack. Until recently, scientists lacked the tools to stitch these fragments into a coherent picture. On average, we found that riverine heat waves occur about half as often as air heat waves, and their temperature increases are a third as intense, but they last nearly twice as long.
More strikingly, their frequency is increasing faster than air heat wave events are. Compared to 1980, an average US river experienced nearly two additional heat wave events in 2022. In 2022, those river heat waves lasted more than three extra days on average than in 1980 and were nearly 1 degree Fahrenheit (almost half a degree Celsius) hotter than in 1980.
Unusual fossil discovery rewrites the history of freshwater fish New research finds that ocean-dwelling fish entered freshwater environments on several occasions, evolving enhanced hearing abilities in the process.
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