Hilsa Fish Research Articles

Post-harvest losses in marine fisheries of Bangladesh

Existing literature highlights significant income loss due to Post-Harvest Loss (PHL) across the fisheries value chain in developing countries like Bangladesh. This is attributed to inappropriate fishing tools, poor infrastructure, inadequate storage facilities, and inefficient transportation. This study estimated PHL and its determinants in Bangladesh's marine fisheries using the Questionnaire Loss Assessment Method (QLAM) based on data collected from 1132 respondents, including fishermen and traders, from October 2019 to March 2021. The results reveal that physical, market, and monetary PHL in marine fisheries are 0.82 %, 6.41 %, and $228.52 per ton, respectively. Annually, the country loses approximately $151 million due to PHL in marine fisheries, with the highest market losses in Snapper, Pomfret, and Hilsa fish. The main reasons for PHL include the duration of fish remain in the net after being caught, insufficient ice, lack of insulated containers and storage facilities, delayed marketing, and oversupply. The study suggests adopting modern harvesting technology, enforcing regulations for scientific gear, and increasing storage capacity at landing and selling points to reduce PHL in marine fisheries.

DNA barcoding of mislabeled juvenile Tenualosa spp. as Gudusia chapra in the fish markets of Bangladesh

Mislabeling of Juvenile hilsa, (Tenualosa spp.) or Jatka fish as Chapila (Gudusia chapra) is a recognized problem in Bangladesh resulting in fraudulence to consumers, illegal harvesting, and ultimately the degradation of hilsa fish production. We applied DNA barcoding using mitochondrial COX 1 gene together with morphometric analysis to resolve the mislabeling or misidentification of Clupeid fishes differentiating mainly hilsa fish from chapila fish. This study confirmed the identification of Jatka fish (Tenualosa sp.) that was mislabeled with chapila (Gudusia chapra). DNA barcoding identified the four species of clupeid fishes (Tenualosa ilisha, Gudusia chapra, Sardinella jussieu and Tenualosa toli) with phylogenetic placement. These cases may reflect a clear picture of admixture of locally sold mislabeled Jatka, which may warrant more comprehensive analyses. Mislabeling records of Juvenile hilsa established in the present study may also have implications for the harvesting, marketing and consumption the national fish of Bangladesh. Bangladesh J. Sci. Ind. Res. 59(2), 105-114, 2024

Length frequency distribution, length-weight relationship and condition factors of Hilsa Shad, Tenualosa ilisha from Bangladesh

Hilsa shad, Tenualosa ilisha, a cherished and economically vital species, thrives in the waters of Bangladesh. It holds a prominent role in bolstering the nation's food security and influencing the ecological dynamics of aquatic ecosystems along the Bangladeshi coast and estuaries. This comprehensive study encompasses data collection efforts on the Hilsa fish species, conducted at 12 commercial landing centers throughout Bangladesh over the course of 2020. The study describes some fundamental components, including length frequency distribution, length-weight relationships, and condition factors, offers invaluable insights into the growth, health, and overall well-being of Hilsa population. Notably, the length-weight relationship analysis revealed size ranges of 11.5-59.2 cm and 11.0-49.0 cm total length for females and males, respectively. The observed b values indicated positive allometric growth (b > 3.00) for female population and negative allometric growth (b < 3.00) for male population in the length-weight relationship. Among the condition factors scrutinized, Fulton's condition factor emerged as the most reliable indicator for assessing the health and condition of the Hilsa population. This study offers valuable insights for biologists, aiding in the assessment of the species' status and providing essential information for fishery biologists and conservation biologists. Such insights are instrumental in the management and ultimate conservation of this iconic species in Bangladesh.

Impact of fishing ban on socioeconomic status of Hilsa fishers in Bangladesh

Fishing ban is a useful regulatory measure for sustainable management and conservation of hilsa shad (Tenualosailisha) in Bangladesh. This study investigated the socioeconomic status of hilsa fishers, as well as their perceptions regarding the performance of fishing bans and coping strategies. Data were collected from 300 fishers residing in the three study areas by using semi-structured questionnaire to collect data related to the livelihood and socioeconomic variables of the fishers. Besides, fishers’ perceptions regarding the performance of the ban as well as income generated from other activities during the fishing ban were also incorporated. Focus Group Discussions (FGD), Crosscheck Interviews (CI) with key informants’ interview was also conducted to collect general information and to justify the collected information. The majority of the fishers feel the bans have resulted in positive socioeconomic impacts which enhance their income and livelihood status from fishing. However, its impact on loss of income and level of unemployment during ban forced some fishers to drive away the ban. In contrast, diversified alternative livelihood options have been adopted by fishers to cope with the ban that not only pull them out from dependency solely on hilsa fishing but also reduce the fishing pressure on the hilsa fishery as well as fish biodiversity. The study showed a positive correlation between fishing ban and resources’ sustainability. In spite of the difficulties faced by fishers during ban, majority of the fishers support the ban for the long-term conservation of hilsa as it is their basic sustenance.

Trace metals in transboundary (India–Myanmar–Bangladesh) anadromous fish Tenualosa ilisha and its consequences on human health

Hilsa shad (Tenualosa ilisha, Hamilton, 1822), the highly coveted table fish within the Indian subcontinent, is Bangladesh's most significant single-species fishery. To assess the risk that toxic metals pose to human health, certain health risk indices—estimated daily intake (EDI), target hazard quotient (THQ), total target hazard quotient (TTHQ), and target cancer risk (TR)—were calculated. The hierarchy of toxic metals (µg/g-ww) in Hilsa shad of the bay showed as Zn (13.64 ± 2.18) > Fe (9.25 ± 1.47) > Mn (2.98 ± 0.75) > Cu (0.57 ± 0.18) > Cr (0.23 ± 0.06) > Pb (0.22 ± 0.04) > As (0.08 ± 0.02) > Ni (0.06 ± 0.02) > Co (0.04 ± 0.01) > Cd (0.01 ± 0.003) in the wet season and Zn (11.45 ± 1.97) > Fe (10.51 ± 1.38) > Mn (3.80 ± 0.75) > Cu (0.73 ± 0.17) > Pb (0.30 ± 0.03) > Cr (0.20 ± 0.05) > As (0.09 ± 0.01) > Ni (0.08 ± 0.02) > Co (0.07 ± 0.02) > Cd (0.02 ± 0.004) in the dry season. The EDI of all the examined trace metals indicated no risk to human health from consuming Hilsa fish. The estimation of THQ and TTHQ suggested that the ingestion of both individual and combined trace metals through Hilsa shad consumption was safe from the perspective of human health. Also, there was no evidence of carcinogenic risk for consumers based on the evaluation of the TR value of metals (As, Pb, Cd, and Ni) due to Hilsa shad consumption.

Gut and flesh microbiome sequencing of the Bangladesh national fish hilsa (Tenualosa ilisha).

The gut and flesh microbiome of the national fish of Bangladesh, Tenualosa ilisha, were analyzed using 16S rRNA gene sequencing. Our findings revealed a significant microbial disparity between sample categories and the habitat of hilsa fish, which will serve as a valuable foundation for further comprehensive studies on the hilsa microbiome.

Bisphenol A contamination in Hilsa shad and assessment of potential health hazard: A pioneering investigation in the national river Ganga, India

The anadromous Hilsa, often known as the "Queen of Fishes" (Tenualosa ilisha), is the most valuable fishery in the Ganga-Hooghly delta estuary. Although BPA exposure has been shown to be harmful to aquatic organisms, no research has looked at the effects of BPA on the commercially valuable Hilsa shad of river Ganga. To close this information vacuum, we examined BPA levels in Hilsa fish from the Ganga estuary. Liver, muscle, kidney, and gonads were all positive for BPA among the Hilsa fish of all ages. Liver BPA levels were highest in adult males (272.16 ± 0.38 ng/g-dw), and lowest in juveniles (5.46 ± 0.06 ng/g-dw). BPA concentrations in the Hilsa shad muscle were highest in reproductively mature females (196.23 ± 0.41 ng/g-dw). The study also discovered a correlation between fish development and BPA exposure, with higher levels of BPA being identified in adult Hilsa species. This is the first study to look at the impact of BPA pollution on aquatic ecosystems and fisheries, and it showed that Hilsa shad is contaminated with BPA and poses health hazards to human beings. The results, which demonstrate BPA contamination, are useful for protecting Hilsa in the river Ganga.

Muscle proteome profile and potential allergens of premature hilsa shad (Tenualosa ilisha)

In this study, for the first time, we profile the actual protein sequences of known and potential allergens of premature hilsa shad (Tenualosa ilisha), an economically important fish of South Asian countries. Proteomics was employed to dissect the muscle tissue proteome collected from the riverine habitat hilsa samples. We successfully identified and quantified >600 proteins wherein many known allergens such as parvalbumins, beta-enolase, and creatine kinases were identified as abundant proteins in muscle tissue. Label-free quantitative proteomics revealed significant differences in the abundance of myosin, dynein, gamma-enolase, creatine kinase B-type, and collagens between the two hilsa samples. In silico analysis determined the allergen potential of these proteins. Notably, our findings indicate that many well-characterized allergen proteins are developmentally regulated in the muscle tissue. Thus, the profiling of a muscle tissue proteome map would further facilitate fundamental and applied research on hilsa fish and greatly improve our understanding of the crucial issue of hilsa customers' nutritional safety.

Understanding the Challenges of the Hilsa Fishing Community in Bangladesh: The River of Life

This study examines the economic, livelihood, and social-environmental conditions of the Meghna Riverbank Hilsa fishermen in the Chandpur region of Bangladesh. The research methods encompassed household surveys, surveys conducted during fishing activities, individual interviews, focus group discussions (FGD), key informant interviews (KII), direct observation, and problem analysis with priority ranking. To gather comprehensive information about the socio-economic conditions and livelihood strategies of the Meghna Riverbank hilsa fishermen, a semi-structured interview schedule was conducted. The findings reveal that these fishermen face exploitation, financial instability, and extreme poverty, relying solely on the river for their income. They lack access to fishing equipment and land due to river erosion, and basic necessities such as family planning, health and sanitation facilities, and education are inadequate. The overall situation is further exacerbated by social and economic constraints, including a growing number of fishermen, low incomes, limited alternative sources of income, loan repayment difficulties, piracy, rising prices, and resource disputes among stakeholders. To improve their standard of living, the study recommends effective interventions, cooperation between government and non-government organizations, and meticulous execution of strategies.

Integrated transcriptome catalog of Tenualosa ilisha as a resource for gene discovery and expression profiling

The silver pride of Bangladesh, migratory shad, Tenualosa ilisha (Hilsa), makes the highest contribution to the total fish production of Bangladesh. Despite its noteworthy contribution, a well-annotated transcriptome data is not available. Here we report a transcriptomic catalog of Hilsa, constructed by assembling RNA-Seq reads from different tissues of the fish including brain, gill, kidney, liver, and muscle. Hilsa fish were collected from different aquatic habitats (fresh, brackish, and sea water) and the sequencing was performed in the next generation sequencing (NGS) platform. De novo assembly of the sequences obtained from 46 cDNA libraries revealed 462,085 transcript isoforms that were subsequently annotated using the Universal Protein Resource Knowledgebase (UniPortKB) as a reference. Starting from the sampling to final annotation, all the steps along with the workflow are reported here. This study will provide a significant resource for ongoing and future research on Hilsa for transcriptome based expression profiling and identification of candidate genes.

Fuel use intensity of hilsa fisheries in the lower Meghna river estuary of Bangladesh

Among the species caught by small-scale fisheries in Bangladesh, hilsa (Tenualosa ilisha) is the most important by volume and of great cultural importance. Hilsa fishing boats have over the last decade been mechanized, enabling longer trips and larger hauls. This development has, however, also resulted in increased fishing pressure and increased reliance on fossil fuels. This study estimates the fuel use intensity (FUI) of hilsa fishing, calculated as fuel per unit landed mass of hilsa at one of the main landing stations (Chairman ghat) in the coastal area of Noakhali district, Bangladesh. Primary data were collected from three types of artisanal fishing boats commonly used in hilsa fisheries, namely small boats (Choto/Khosa tempo), medium boats (Tempo), and large boats. Our results show a higher fuel use intensity in small boats (750 ± 468 l t-1), compared to medium (495 ± 270 l t-1) and large boats (576 ± 365 l t-1). Considering the gross catch and total fuel consumption of all boats, the absolute FUI is estimated at 463 l t-1. Thus, the FUI of hilsa fishing is slightly lower than the average for global fisheries FUI (489 l t-1). In terms of greenhouse gas (GHG), not including other lifecycle inputs (e.g. infrastructure, ice, supply chain etc.) than fuel (i.e. diesel, LPG, and wood), the average global warming impact is 1.72 ± 0.34 tonnes CO2-eq. t-1 overall catch. This study provides a baseline estimate for FUI and GHG emissions from contemporary hilsa fishing, and proposes solutions for addressing environmental issues and improving the overall performance of the sector.

Bacillus velezensis BNC -1, a Novel Salt-Tolerant Biocontrol Agent Obtained from Salted Hilsa Fish Prohibits the Growth of Vegetable/Fruit Pathogen

Bacillus velezensis BNC -1, a Novel Salt-Tolerant Biocontrol Agent Obtained from Salted Hilsa Fish Prohibits the Growth of Vegetable/Fruit Pathogen

Socioeconomic, livelihood and cultural profile of the Meghna River Hilsa Fishing Community in Chandpur, Bangladesh

The goal of the study was to build a comprehensive portrait of the socioeconomic, livelihood, and cultural profile of the Meghna River fishing community in Chandpur, Bangladesh. Shatnol Malopara, an ecologically and economically suitable fishing community under the Matlab Uttor Upazila of Chandpur district, was selected for the in-depth investigation, where 410 fishermen relied solely on fishing for their livelihood. This community is made up of 185 households, supporting close to 1000 people. They are all Hindus, and fishing was their ancestral profession. A well-structured questionnaire was used to collect the data. The research revealed that the majority (35%) of fishermen were in the 18-30 age range. The community preferred nuclear families (98%), and the average family size was 5-8 individuals, which is predominant at 80%. About 60% of households lived in tiny tin shades and 40% in medium tin shades, while 60% did not have their own land. They (80%) rely on solar energy for illumination and for health facilities 50% of fisher households depend on the local pharmacy to take medication. Almost 100% of the residents in this community used potable drinking water, and 50% of fishers have ring slab latrines while the other 50% have pits. According to the survey, 60% of fishermen were very poor, 20% were poor, and 20% were moderately poor. Based on the survey, the majority (70%) of the fishermen earned between the ranges of 3000-5000 BDT (Bangladesh Taka) per month. During the ban period, the majority of fishers (50%) took out loans from various sources. Non-governmental organizations that operate microcredit businesses provided 70% of the loans to fishermen. According to the survey, 32% of fishermen had a boat and gear, while 68% worked as labor or engaged in catch-sharing with Mohajons' boats and gear. A range of crafts (Dingi nouka, Kosa nouka with mechanization) and fishing gear (Kona jal, Gulti jal, Dhon jal, Chap jal, Bada jal, Current jal, Chewa jal, etc.) was observed to be used in the study area. They have a plethora of traditional ecological knowledge as a result of their fishing ancestors. The study revealed that hilsa fishermen had a variety of issues. Extortion by local extortionists was the principal concern; other issues included inadequate credit and alternative income sources during the ban period. To assist the community in raising its standard of living, government agencies, nonprofits, and other relevant groups of organizations should adopt a number of steps. It is imperative to prioritize alternative income-generating options in this context.

Dominant phytoplankton groups as the major source of polyunsaturated fatty acids for hilsa (Tenualosa ilisha) in the Meghna estuary Bangladesh

The tropical estuarine ecosystem is fascinating for studying the dynamics of water quality and phytoplankton diversity due to its frequently changing hydrological conditions. Most importantly, phytoplankton is the main supplier of ω3 polyunsaturated fatty acids (PUFA) in the coastal food web for fish as they could not synthesize PUFA. This study evaluated seasonal variations of water quality parameters in the Meghna River estuary (MRE), explored how phytoplankton diversity changes according to hydro-chemical parameters, and identified the major phytoplankton groups as the main source of PUFA for hilsa fish. Ten water quality indicators including temperature, dissolved oxygen, pH, salinity, dissolved inorganic nitrogen (DIN = nitrate, nitrite, ammonia) and phosphorus, dissolved silica and chlorophyll-a were evaluated. In addition, phytoplankton diversity was assessed in the water and hilsa fish gut. Principal component analysis (PCA) was used to analyze the spatio-temporal changes in the water quality conditions, and the driving factors in the MRE. Four main components were extracted and explained 75.4% variability of water quality parameters. The most relevant driving factors were dissolved oxygen, salinity, temperature, and DIN (nitrate, nitrite and ammonia). These variabilities in physicochemical parameters and dissolved inorganic nutrients caused seasonal variations in two major groups of phytoplankton. Peak abundance of Chlorophyta (green algae) occurred in water in nutrient-rich environments (nitrogen and phosphorus) during the wet (36%) season, while Bacillariophyta (diatoms) were dominant during the dry (32%) season that depleted dissolved silica. Thus, the decrease of green algae and the increase of diatoms in the dry season indicated the potential link to seasonal changes of hydro-chemical parameters. The green algae (53.7%) were the dominant phytoplankton group in the hilsa gut content followed by diatoms (22.6%) and both are contributing as the major source of PUFAs for hilsa fish according to the electivity index as they contain the highest amounts of PUFAs (60 and 28% respectively).

An Assessment of the Water Quality Factors: A Case of Hilsa Fishery River Areas

The physicochemical and biological attributes of a river ecosystem usually reveal the status of the subsistent aquatic life and affiliated species richness index of the biodiversity. Towards appraisal of water quality, physicochemical parameters (i.e., temperature, pH, DO, transparency and conductivity), water nutrients (nitrate, phosphate) and concentration of chlorophyll a were determined. Samples were collected from seven different stations of Hilsa fishery areas with their special feature. The study revealed a slight spatial variation in physicochemical parameters of river water. While the parameters were found to be at acceptable levels, some measures are needed to improve the quality of water to ensure successful migration and reproduction of the Hilsa fish. The water quality parameter was found slightly alkaline (7.4±0.3). The transparency was found (38.3±11.11 cm) followed by water temperature (22.47±01.79 ºC), alkalinity (101.8 ±19.87), conductivity (2139±2101 µS/cm), CO2 (6.79±2.43 mg/L), DO (7.56±0.38 mg/L), nitrate (0.006±0.01 g/L), phosphate (0.002±0.0003 mg/L). Chlorophyll a, which represents the biomass of phytoplankton, was estimated (4.58 ± 4.18 mg/L). The largest quantity of plankton as a natural food (both in number and taxa) was found in the Meghna river basin compared to the other rivers. This assessment of the physical, hydrological, chemical and biological profile of the environment of the Hilsa fishery areas of the country delivers obvious evidence which is important to the apprising of the hilsa fisheries management action plan and to the sustainable management of hilsa fishery to a greater extent.

Fish availability and market channel in Rajbari, Bangladesh

Knowledge about fisheries market margins and fish availability in the market is crucial to establish an effective and well-planned marketing strategy. Hereby, the study was conducted to bring some knowledge on the availability of raw and processed fish and its marketing channel in Rajbari Sadar, Bangladesh from June to December 2020. Here, data were collected from fish traders and consumers of the target markets through questionnaire surveys, focus group discussions and field visits. The study found 107 fish and shellfish species in these markets, of which more than 50% species were commonly available and less than 10% were found very rarely. The study also observed 18 types of processed fish products in these markets including dried (77.77%), salted (16.67%) and fermented (5.56%) products arriving from mostly Dhaka and Chattogram. The markets were dominated by wild freshwater fishes of nearby rivers, ponds and canals etc. The length of processed and marine fish marketing channel was comparatively longer than freshwater one because these items are supplied here from coastal districts via several intermediaries. The study revealed remarkable market margin for hilsa fish even noticed up to 57.14% at consumer level. There was also observed some major constraints to a good marketing system such as unplanned market location, insufficient drainage system, high transportation cost, etc. Based on the constraints, the study would suggest to establish a well-planned and modern equipped fish market with high quality cold storage and ice factories, which could help to ensure smoother transaction route from production to customer minimizing economic loss.

Study of the spawning season of Hilsa, Tenualosa ilisha in Bangladesh

An experiment was carried out on the reproductive biology of riverine populations of Tenualosa ilisha in Bangladesh to identify peak breeding season using gonadal biology and gonadosomatic index (GSI) information, reproductive and fry production potentiality, which will finally lead to development strategies for conservation of Hilsa fish species. Total 480 Samples were collected from Meghna River, Chandpur, from July 2012 to June 2013 and Tentulia River, Barisal from June 2013 to June 2014. Both Total length (TL) and Gonad length (GL) were measured using a measuring scale, and both Body weight (BW) and Gonad weight (GW) were taken using an electric balance. To detect the peak spawning activity of hilsa of the Meghna River and Tentulia River, the GSI and Dobriyal index (DI) were calculated. The mean GSI value for both female and male hilsa of the Meghna River was found to be varied from 4.84±0.63 to 15.31±1.17 and 0.32±0.04 to 1.04±0.08, respectively, with the highest value in October. In the case of the Tentulia River, the mean GSI value for female and male hilsa was found to be varied from 6.33±0.39 to 15.03±0.37 and 0.32±0.03 to 1.00±0.06, respectively, with the peak in October. Mean DI of female and male hilsa of Meghna River, Chandpur was found to be ranged from 3.31±0.23 to 5.15±0.17 and 1.18±0.04 to 1.71±0.03 respectively, and October was the highest. Mean DI value of female and male hilsa of Tentulia River, Barisal varied from 3.63±0.15 to 5.00±0.12 and 1.18±0.04 to 1.70±0.03 respectively, with the peak in October. Both the GSI and DI results of the present study suggested that hilsa has a prolonged spawning season, but major spawning takes place in October–November, with a distinct peak in October, indicating the peak spawning season for hilsa in Bangladesh.

Organ-specific accumulation of toxic elements in Hilsa shad (Tenualosa ilisha) from Bangladesh and human health risk assessment

Purpose: We aimed to determine the amount of some toxic elements in three organs of Hilsa shad, focusing on the possible exposure to human health through Hilsa consumption. This study was designed to determine the concentration of seven toxic trace elements (As, Cd, Cr, Cu, Ni, Pb, and Zn) in three distinct organs (n = 21) (muscle, liver, and gills) of Hilsa shad (Tenualosa ilisha) fish collected from the Bangladeshi coastal area. The samples were digested following a microwave digestion. Inductively coupled plasma mass spectrometer was used as analytical instrument. Estimated daily intakes (EDI) and target cancer risk (TR) were used to evaluate carcinogenic and non-carcinogenic risk. Results: The mean concentrations (mg/kg-wet weight) of toxic elements in different organs of T. ilisha were determined as follows: in muscle, As (4.05), Cd (0.09), Cr (0.12), Cu (0.77), Ni (0.26), Pb (0.20), and Zn (10.64); in liver, As (2.83), Cd (0.84), Cr (0.18), Cu (6.17), Ni (0.55), Pb (0.23), and Zn (30.16) and in gills, As (3.45), Cd (0.05), Cr (0.08), Cu (1.06), Ni (0.51), Pb (0.78), and Zn (35.21). The liver showed higher concentrations of most elements than that of muscle except for As. Concentration of As, Cd, and Pb in the fish were found above the food safety guidelines, while other trace element concentrations were below the permissible range for human consumption. According to EDI and TR values, there were carcinogenic and non-carcinogenic risks from exposure to total As concentration from Hilsa fish consumption. Conclusion: This study suggests that the toxic trace elements contamination levels in Hilsa fish from Bangladesh’s coastal area need to be monitored on a systematic and regular basis to ensure the safety of this food item for human consumption.

Life at the borderline: Responses of Ganges river dolphins to dry‐season flow regulation of river and canal habitats by the Farakka barrage

Abstract Modification of river flows by dams and barrages has fragmented riverine habitats and threatened the survival of Indian subcontinental river dolphins. In this study, habitat use by endangered Ganges river dolphins in response to dry‐season operations (December‐March) of the Farakka barrage on the Ganga River, located about 20 km upstream of the India–Bangladesh border, was assessed. Ten surveys were conducted in: (i) the Ganga River below the barrage, where rapid changes in water levels were expected owing to barrage operations; (ii) the Farakka feeder canal with stable water levels; and (iii) the Hooghly River downstream of the canal. Dolphin distribution, water depth, fishing boat count and temperature were recorded in all surveys and the data were analysed in a dynamic occupancy modelling framework. Temporal trends in river discharge, primary productivity and fish availability were also estimated to explain river dolphin responses. Occupancy and colonization by dolphins increased in all stretches by spring/March, correlated with rising water temperature and increased fishing intensity, which was related to upstream migration of hilsa fish. In the Ganga River, dolphin occupancy in deep river pools remained stable, but resulted in increased overlap with fisheries as river flow declined. The feeder canal, with stable flows, witnessed increased colonization by dolphins, but also greater risk of bycatch in fishing nets. The canal that appeared as a hydrological refuge thus became an ‘ecological trap’. The findings highlight the need for integration of flow maintenance and fishery regulations in the monitoring and management of canals as effective refuges for riverine species. We advocate the inclusion of ecological flow criteria and fishery regulations to reduce dolphin bycatch mortality, in the context of establishing river dolphin conservation plans and transboundary water‐sharing guidelines. The revision of the India–Bangladesh water‐sharing treaty in 2026 could incorporate the above considerations.

Determination of arsenic, cadmium, selenium, zinc and other trace elements in Bangladeshi fish and arsenic speciation study of Hilsa fish flesh and eggs: Implications for dietary intake

Exposure to As from drinking water and its impact on the health of the Bangladeshi population has received much attention. However, very little information is available regarding As exposure through consumption of fish, which is the main source of animal protein for the majority of Bangladeshis. In this study, concentrations of As, Cd, Pb, Mn Se and Zn in different types of fish, consumed by Bangladeshis, were determined using Inductively Coupled Plasma Mass Spectrometry. Daily intakes of the toxic elements As, Cd and Pb through fish consumption were estimated to be 31.8, 0.4 and 4.8 μg/day, respectively. Hilsa (Tenualosa ilisha) contained the highest concentrations of total As (mean ± SD was 2.55 ± 1.3 mg/kg; n = 15) among the fish analysed. However, toxic inorganic As species were not detected. The dominant As species in Hilsa fish were: dimethylarsenic acid, arsenobetaine and arsenosugars, at 69, 11 and 20% of total As, respectively. The high concentration of Cd detected in Hilsa eggs (average 278 ± 518 μg/kg; range 7.4–1725 μg/kg; n = 10) is of concern since this may have harmful effects on the development of embryos and lead to a decline in the Hilsa population or the quality of the fish. It can also be harmful to those who consume Hilsa eggs on a regular basis. Selenium was found to be highest in Shoal (Micropterus cataractae) fish and a type of small fish, and lowest in Mrigal (Cirrhinus cirrhosis). Small fish species contained Mn and Zn at 7.1- and 4.3-fold higher concentrations, respectively, compared to big fish species. Keski (Corica soborna), a small fish species, contained by far the highest concentrations of Mn (52 mg/kg) and Zn (140 mg/kg), although the concentration of As (1.4 mg/kg) in this fish was lower than that of several other fish species. Small fish species are often consumed whole, including the bones, and therefore the essential trace elements present are potentially bioavailable for cellular metabolism. Our study shows that the Bangladeshi population can easily meet their daily requirement of Se and Zn from consumption of fish such as Shoal fish (Se and Zn), Hilsa fish (Se and Zn) and Keski fish (Se and Zn). Consumption of small fish (such as Keski) and big fish (such as Hilsa) from Bangladesh can provide valuable sources of essential trace elements as part of a balanced diet and thus negate the need for supplements and biofortification of certain foods. Ours is a small study and a detailed total dietary intake and human biomonitoring studies, that includes coverage of different socio-economic groups, are needed in Bangladesh before giving people supplements or biofortified foods.