Biology and fisheries of Hilsa shad in Bay of Bengal

Proximate and fatty acid compositions oft en wild-caught and farmed fish species in mato grosso state, brazil

This study analyzed ten fish species (three farmed and seven wild-caught) to determine their centesimal composition (assessed by AOAC methods) and lipid profile (analyzed by GC-MS). Notably, "tambatinga" (farmed) and "piraputanga" (wild-caught) stood out with 28.66 % and 26.44 % protein content and 2.32 % and 3.71 % lipid content, respectively. Across all species, oleic acid was the predominant fatty acid, followed by linoleic acid. The sum of PUFAs ranged from 17.84 % in "matrinchã" to 7.85 % in "piraputanga". SFA varied from 49.93 % in "tambacu" to 39.90 % in "matrinchã", while MUFAs ranged from 44.34 % in "palmito" to 38.39 % in "tambaqui". "Matrinchã" had the highest average ω6 acid content (16.83 %), while "cachara" had the highest average for ω3 acids (5.73 %). "Piraputanga". "cachara", and "pincachara" exhibited the lowest ω6 levels. The analysis shows that fish have excellent nutritional values (proximate compositions) with few differences between species. "Pacu", "matrinchã", and "cachara" (wild-caught) demonstrated positive attributes, while "pincachara" (farmed) exhibited the highest nutritional quality in terms of fatty acid fraction. Based on quality indices (H/H), "pacu", "matrinchã" and "pincachara" are recommended choices for a healthy diet. This study adds valuable insights into the nutritional composition of fish species, which is essential for promoting regional development and local aquaculture.

Diadromy Drives Elevated Rates of Trait Evolution and Ecomorphological Convergence in Clupeiformes (Herring, Shad, and Anchovies)

AbstractMigration can have a profound influence on rates and patterns of phenotypic evolution. Diadromy is the migration between marine and freshwater habitats for feeding and reproduction that can require individuals to travel tens to thousands of kilometers. The high energetic demands of diadromy are predicted to select for ecomorphological traits that maximize swimming and locomotor efficiency. Intraspecific studies have shown repeated instances of divergence among diadromous and nondiadromous populations in locomotor and foraging traits, which suggests that at a macroevolutionary scale diadromous lineages may experience convergent evolution onto one or multiple adaptive optima. We tested for differences in rates and patterns of phenotypic evolution among diadromous and nondiadromous lineages in Clupeiformes, a clade that has evolved diadromy more than 10 times. Our results show that diadromous clupeiforms show convergent evolution for some locomotor traits and faster rates of evolution, which we propose are adaptive responses to the locomotor demands of migration. We also find evidence that diadromous lineages show convergence into multiple regions of multivariate trait space and suggest that these respective trait spaces are associated with differences in migration and trophic ecology. However, not all locomotor traits and no trophic traits show evidence of convergence or elevated rates of evolution associated with diadromy. Our results show that long-distance migration influences the tempo and patterns of phenotypic evolution at macroevolutionary scales, but there is not a single diadromous syndrome.

Living in a hypoxic world: A review of the impacts of hypoxia on aquaculture

Hypoxia is a harmful result of anthropogenic climate change. With the expansion of global low-oxygen zones (LOZs), many organisms have faced unprecedented challenges affecting their survival and reproduction. Extensive research has indicated that oxygen limitation has drastic effects on aquatic animals, including on their development, morphology, behavior, reproduction, and physiological metabolism. In this review, the global distribution and formation of LOZs were analyzed, and the impacts of hypoxia on aquatic animals and the molecular responses of aquatic animals to hypoxia were then summarized. The commonalities and specificities of the response to hypoxia in aquatic animals in different LOZs were discussed lastly. In general, this review will deepen the knowledge of the impacts of hypoxia on aquaculture and provide more information and research directions for the development of fishery resource protection strategies.

The Premium of Hilsa Sanctuary: A Socio-Economic and Ecological Evaluation from the Meghna Estuary, Bangladesh

Sanctuaries are widely regarded as a protected area where fishing has been placed under some restrictions by local, state, regional and national authorities for the conservation and management of fisheries resources. These sanctuaries have a broad array of positive and negative social, economic, cultural and political impacts on fishers. This study aims to analyze the socio-economic and ecological benefits and costs of hilsa sanctuaries to protect single most important hilsa species using Sustainable Livelihood Approach (SLA). Under the Protection and Conservation of Fish Act of 1950, six sites along the Padma, Meghna, Tetulia, and Andharmanik rivers have been designated as hilsa sanctuaries. Findings of the current study revealed that most fishers perceived production of hilsa and other species were increased as a direct consequences of sanctuaries establishment. However, a considerable proportion of hilsa fishermen was found to have low socioeconomic capital, as measured by monthly income, housing circumstances and asset ownership. During the restricted fishing season in the sanctuaries, these households are particularly vulnerable to food insecurity. The government’s compensation scheme is a good example of payment of ecosystem services in an open water fishery; however, this scheme does not include all the affected fishers. It is found that hilsa sanctuaries lead to income loss of the poor fishers which is insufficiently compensated by government support program. To compensate income loss, fishers resort illegal fishing which undermine the success of sanctuary. If the sanctuaries are to function effectively, affecting fishers must be addressed by offering enough compensation schemes so that fishers are able to support their families. Moreover, some fishers believed that a co-management approach involving fishers and government is the possible best management option for operating sanctuaries in a sustainable way.

Microplastics in an anadromous national fish, Hilsa shad Tenualosa ilisha from the Bay of Bengal, Bangladesh

Hilsa shad is one of the most important fisheries, contributing about 12.9% of the country's (Bangladesh) total fish production. There was no previous study on microplastic contamination of this important commercial fish. This study aims to identify, classify, and quantify microplastics (MPs) ingested by the national fish of Bangladesh, Hilsa shad, Tenualosa ilisha. A total of 287 MPs were recovered from the gastrointestinal tracts. All the fishes analyzed were contaminated with MPs. The mean (±SD) of the number of MPs was 19.13 ± 10.77 particles/fish, ranging from 7 to 51 particles/fish. Significant correlation was not found between the fish body length and MP abundance (rs = 0.287, p = 0.299), and between the fish body weight and MPs abundance (rs = 0.261, p = 0.347). The most dominant color was transparent (30%), followed by gray and black, contributing to 26% and 23%, respectively. The maximum number of MPs accounted for in the 300-1500 μm size class where fiber was the most dominant (50%) shape of observed MPs. These results provide a baseline of MP contamination in seafood from Bangladesh that should be useful for future monitoring efforts. The present study is the first research on MP contamination of Hilsa shad.

Conservative Scoring Approach in Productivity Susceptibility Analysis Leads to an Overestimation of Vulnerability: A Study from the Hilsa Gillnet Bycatch Stocks of Bangladesh

Despite different approaches used to assign the risk scores for missing information in productivity susceptibility analysis (PSA)—a widely used semi-quantitative risk assessment tool for target and non-target fisheries stocks—for the selected attributes of a given species, no formal comparison has been made between scoring approaches in terms of how well they can predict species vulnerability. The present study evaluated the PSA findings of 21 bycatch stocks of the Hilsa (Tenualosa ilisha) gillnet fishery of Bangladesh using two different scoring approaches (the conservative scoring approach, CSA; and the alternative scoring approach, ASA) to determine the most reliable approach to minimize false estimates of species vulnerability. Our analysis revealed that the V scores increased by 0.0−0.20 with a mean value of 0.09 for 21 selected bycatches when CSA was applied. The inconsistency between the vulnerability (V)-score-suggested fishing status (V ≤ 1.8 = underfishing, V > 1.8 = overfishing) and the fishing status defined by exploitation rate (E > 0.5 = overfishing, E < 0.5 = underfishing) were 38.1% and 19.0% under CSA and ASA, respectively. Likewise, the consistency between the V-score-suggested fishing status and fishers’ perceived catch trends was found to be higher when using ASA than when using CSA. Our analysis suggests that CSA could overestimate species vulnerability. Therefore, ASA is more reliable than CSA in PSA, which may increase the confidence of fisheries stakeholders in PSA.

Cross-species gene enrichment revealed a single population of Hilsa shad (Tenualosa ilisha) with low genetic variation in Bangladesh waters

Tenualosa ilisha is a popular anadromous and significant trans-boundary fish. For sustainable management and conservation of this fish, drawing an appropriate picture reflecting population status of this species is very essential based on their all-strategic habitats in Bangladesh. In this study, 139 samples from 18 sites were collected and cross-species gene enrichment method was applied. Like most of the Clupeiforms, nucleotide diversity of this shad was very low (0.001245-0.006612). Population differences between most of the locations were low and not significant (P > 0.05). However, P values of a few locations were significant (P < 0.05) but their pairwise FST values were very poor (0.0042-0.0993), which is inadequate to recognize any local populations. Our study revealed that the presence of a single population in the Bangladesh waters with some admixtured individuals, which may contain partial genes from other populations. Most of the individuals were admixed without showing any precise grouping in the ML IQtree and Network, which might due to their highly migratory nature. Fishes from haors and small coastal rivers were not unique and no genetic differences between migratory cohorts. The hilsa shad fishery should be managed considering it as a single panmictic population in Bangladesh with low genetic diversity.

Reproductive environment of the decreasing Indian river shad in Asian inland waters: disentangling the climate change and indiscriminative fishing threats

The regional climate has significantly warmed with erratically declining annual rainfall and intensified downpour within a narrower span of monsoon months, which led to an increased trophic state (≈algae) in most inland waters. Freshwater clupeids vitally control the aquatic food chain by grazing on algae. Despite increasing food availability, IUCN Red List® revealed 16 freshwater clupeids with a decreasing population trend. We investigated one such species' reproductive dependencies, Gudusia chapra (Indian river shad), in the lower Gangetic drainage (India) under a mixed context of climate change and overfishing. Monthly rainfall (≥ 60-100 mm) and water temperature (≥ 31-32 °C) are key breeding cues for females. The regional climate seems inclined to fulfill these through the significant part of the breeding season, and indeed the species has maintained consistent breeding phenology over 20 years. Other breeding thresholds relevant to fishing include size at first maturity (≥ 6.8 cm; reduced by ~ 25-36%) and pre-spawning girth (Girth_spawn50 ≥ 7 cm; first record). Girth_spawn50 is a proxy of the minimum mesh size requirement of fishing nets to allow safe passage of "gravid" females (+ 22% bulged abdomen) and breed. The operational fishing nets (3-10 cm mesh) probably have been indulged in indiscriminative fishing of gravid females for generations. Under a favorably changing climate and food availability, existing evidence suggests a fishery-induced evolution in regional females (to circumvent such mesh sizes) through earlier maturation/puberty at smaller sizes. It could be an early warning sign of population collapse (smaller females → lessening fecundity → fewer offspring). Overfishing seemed to be a bigger threat than climate change.

Organochlorine pesticides and heavy metals in the zooplankton, fishes, and shrimps of tropical shallow tidal creeks and the associated human health risk

Studies on organochlorine pesticides (OCPs) and heavy metals (HMs) from tidal creeks are scarce. Sixteen OCPs and seven HMs were measured in the surface water, zooplankton, two fishes (Harpadon nehereus and Pampus argenteus), and one shrimp (Penaeus indicus) collected from three tidal creeks of the Indian Sundarban. The surface water was polluted by hexachlorocyclohexane isomers (ΣHCH: 525-1581 ng l^-1), dichlorodiphenyltrichloroethane congeners (ΣDDT: 188-377 ng l^-1), endosulfan congeners (ΣEND: 687-1474 ng l^-1), and other OCPs (512-1334 ng l^-1). However, the mean HM concentrations in the surface water were <1 μg l^-1. The zooplankton community exhibited bioaccumulation of both OCPs and HMs. Aldrin, Heptachlor, and α-HCH levels in the edible biotas could lead to cancer. Co and Cd levels could lead to non-cancerous risks, and Pb levels could pose a cancerous risk. This study showed that creeks could be potential sites of both OCP and HM pollution.

Climate Change Impacts on a Tropical Fishery Ecosystem: Implications and Societal Responses

The present study aimed to map out the current threats and anticipated impacts of climate change on the most important hilsa shad (Tenualosa ilisha) fishery and the associated fishing communities based on fieldwork in six coastal fishing communities. To collect empirical data, individual interviews, focus group discussions, oral history, and key informant interviews were conducted. To supplement the empirical findings, time-series data of cyclones and sea-borne depressions in the Bay of Bengal were also analyzed. Analysis of secondary data regarding climate change-induced events and regional studies suggested that the biophysical conditions of the Bay of Bengal are likely to be aggravated in the future, potentially causing more frequent extreme events and affecting the livelihoods of coastal fishing communities in Bangladesh. The fisher respondents revealed that the main target hilsa shad fishery is particularly vulnerable to climate change in terms of alterations to migration patterns and breeding and growth performance. The fishers reported constant climate-related risks because they live in seafront locations, exposed to extreme events, and their occupation entails risky sea fishing. Fishers claimed that they often need return to the coast due to unsuitable weather conditions related to cyclones and frequent tropical depressions, which can cause financial losses or even causalities. Such events negatively affect fishers’ livelihoods, and wellbeing. To cope with the impacts of climate change the fishers have adopted various strategies at both sea fishing and household levels. However, these strategies only support the fishers in terms of immediate survival; they are not enough for long-term resilience. To improve the resilience of the hilsa fishers, the study argues for the implementation the Small-Scale Fisheries Guidelines (SSF Guidelines), which call for longer-term development goals, including in the immediate relief phase, and rehabilitation, reconstruction, and recovery to reduce vulnerabilities to climate and anthropogenic risks.

Governance and Power Dynamics in a Small-Scale Hilsa Shad (Tenualosa ilisha) Fishery: A Case Study from Bangladesh

This paper considers the hilsa shad (Tenualosa ilisha) fishery of southern Bangladesh as a case study regarding governance and power dynamics at play in a small-scale fishery, and the relevance of these for the sustainable management of coastal fisheries. Qualitative methods, involving in-depth individual interviews (n = 128) and focus group discussions (n = 8) with key stakeholders in the hilsa fishery, were used to capture multiple perspectives on governance from those in different positions in the relative power structures studied, while facilitating insightful discussions and reflections. The analysis here is based on a power cube framework along three power dimensions (levels, spaces, and forms) in Bangladesh’s hilsa fishery. The study displays an imbalance in the present hilsa governance structure, with some stakeholders exercising more power than others, sidelining small-scale fishers, and encouraging increasing illegal fishing levels that ultimately harm both the fisheries and those dependent on them. To overcome this, we propose a co-management system that can play a vital role in equalizing power asymmetry among hilsa fishery stakeholders and ensure effective hilsa fishery governance. Our results suggest that recognizing analyzed power dynamics has substantial implications for the planning and implementation of such co-management and the long-term sustainability of the hilsa fishery.