Exotic fish and decreasing habitats vis-à-vis conservation of freshwater fish biodiversity of Bangladesh

Multiple stressors including biological invasion have long been recognised in conservation of freshwater fish biodiversity. Works in this line have, however, been still scanty in Asia and South America – the continents known for rich biodiversity. In this study, the first of its type in Bangladesh, impacts of exotic fish and declining habitats on native fishes have been investigated. Regression and correlation analyses of 16 years production data of ponds, practically the only habitat where exotic fish are cultured commonly with indigenous ones, reveals that a maximum of 25% of the abundance decrease of native fish could be due to the effects of five commonly cultured exotic fish. Rest of the decline might largely be due to shrinkage, degradation, and destruction of habitats. Inland habitats other than ponds shrink, commonly, by about 80 % during the dry season, and most rivers are heavily polluted except for the brief mid rainy season. Decline in native fish populations may result in reduced genetic diversity. Another potential danger is the probable genetic introgression from the less fit hatchery-originated fish with the wild ones. The study concludes that the native freshwater fishes are endangered by declining habitats, exotic fishes, genetic consequences of hatchery supplementatio

Mud crab fishery in climate vulnerable coastal Bangladesh: an analysis towards sustainable development

Developing countries are far more vulnerable to climate change impacts than industrialised countries. Most of the world’s poor live in South Asia where they have limited livelihood options that have become even narrower in recent years, indicating a need for alternative income-generating options. Mud crabs (Scylla spp.) are considered to have promising prospects in different parts of the world including Bangladesh, a well-known region for its vulnerability to climate change. At present, this fishery has become a growing venture in coastal Bangladesh, primarily due to the potential of the export market and availability of seed locally. This study included a calculation of the Human Development Index linked to mud crab fishery (HDIMCF) and a strengths, weaknesses, opportunities and threats (SWOT) analysis to clarify the present status of and strategic directions for the mud crab fishery, for the first time. Results revealed an intermediate level of development of mud crab aquaculture, indicating potential alternative livelihood opportunities for vulnerable coastal communities. The SWOT analysis revealed that positive factors, both internal (strengths) and external (opportunities), predominate over negative factors (weaknesses and threats) and that the fishery can be an alternative livelihood option for vulnerable coastal communities. Despite noticeable diversification of the mud crab fishery, dependence on wild seedstock and possible over-exploitation in the wild appear to constrain sustainable development of the fishery. This study’s findings suggest undertaking immediate wild crab stock assessment for determining current status of wild populations. Moreover, modification of the Government of Bangladesh’s existing mud crab policy is needed to better meet growing demand and sustainability of the fishery. Recommendations of this study may be of help in guiding responsible integrated coastal fisheries management and policy

Stakeholders' knowledge of threatened freshwater fishes and their involvement in fishery value chains in order to assist conservation in developing countries

Introduction: Improved conservation of exploited freshwater biodiversity is an increasing priority globally, but in developing countries there is often little insight of stakeholder attitudes within the value chains through which exploited species are passed, upon which to make informed management decisions. Methods: We determined knowledge concerning threatened freshwater fishes in Bangladesh by key stakeholder groups (fishermen, faria agents, commission agents, retailers and consumers; n = 485 respondents) and their participation level in the threatened fish value chain. We also determined factors affecting local ecological knowledge and participation in the value chain. Results and discussion: The highest mean number of threatened fish species (4.8 ± 3.5% of species) was identified by the fishermen group, whereas consumers identified fewest (0.5 ± 1.1% of species). All respondent groups participated in the threatened fish value chain and their participation varied across respondent groups. 45.3% of the total number of threatened fish species appeared in the value chain. Participation level was highest for commission agents, involved in the trade of 21.5 ± 4.2% of threatened fish species, and lowest for consumers (7.4 ± 6.5% of threatened species). For fishermen, the principal component “experience-income-age” and the interaction between education and financial loan factors affected fishers' participation in the threatened fish value chain positively whereas, this was negatively affected by their knowledge level of threatened fishes. This study reveals the poor knowledge of stakeholder groups regarding threatened fishes, but establishes their active participation in the value chain of these species in Bangladesh. With limited resources for conservation of threatened species in many developing countries, it is very risky to implement commonly used in-situ conservation methods (e.g., habitat quality improvement) without fuller buy-in from the stakeholders. Conclusions: We recommend specific protection laws for threatened fishes and awareness building campaigns for stakeholder groups to ensure minimum impact to threatened fish species. As overharvesting is a major cause of threatened fish species decline, such training programmes should be designed for fishers in developing regions. Education programmes on threats to ecosystems and biodiversity should be prioritized in schools and fishing communities. In addition, regular monitoring for protected species at harvesting sites and fishing markets should be ensured

Rapid response of fish and aquatic habitat to removal of a tidal barrier

River barrier removal is used increasingly as a conservation tool to restore lotic habitat and river connectivity, but evidence of its efficacy is incomplete. This study used a before–after methodology to determine the effects of removing a tidal‐limit barrier on the fishes, macroinvertebrates, and habitats of an English coastal stream. Following barrier removal, habitat diversity increased immediately upstream and remained similar downstream. Mobilized silt altered the substrate composition immediately downstream, but this was temporary as silt was flushed out the following winter. Changes to macroinvertebrate communities occurred upstream and downstream of the former barrier but these were transient. A dramatic and sustained increase in fish density occurred immediately upstream of the barrier after its removal, but effects downstream were minor. The fish community upstream changed, largely due to rapid recruitment and dispersal of endangered European eel (Anguilla anguilla). Eel density in the formerly impounded zone increased from 0.5 per 100 m2 before barrier removal to 32.5 per 100 m2 5 months after removal. By 17 months after barrier removal there was no difference in eel density across the six sections sampled. Although resident stream fishes such as bullhead (Cottus gobio species complex, protected under the European Habitats Directive) were abundant in middle and upper‐stream sections, brown trout (Salmo trutta, a listed species for biodiversity conservation in England and Wales) density remained low during the study and recruitment was poor. This suggests that although colonization access for anadromous trout was available, habitat upstream may have been unsuitable for reproduction, indicating that wider catchment management is required to complement the restoration of connectivity. These findings suggest that tidal barrier removal is an effective method of restoring lotic habitats and connectivity, and can be beneficial for resident and migratory fishes including those of conservation importance (e.g. European eel) in coastal streams

Strong impacts of signal crayfish invasion on upland stream fish and invertebrate communities

1. Impacts of invasive signal crayfish Pacifastacus leniusculus on native species and ecosystems are widely recognised, but mostly through small‐scale studies and laboratory experiments that may not always reflect impacts in nature. Recorded effects of signal crayfish on fish populations are equivocal. In this study, using the before–after/control–impact and control–impact approaches, the effects of signal crayfish invasion on native fishes, particularly benthic fishes and young‐of‐year (YoY) salmonids, and macroinvertebrate communities, were determined on several spatial and temporal scales through three correlated study elements (S1–S3), in upland streams of the River Tees, England. In S1, we sampled fish and benthic macroinvertebrates of 18 streams identically in 2011 and 2018. These streams were categorised into two groups: (1) uninvaded (without signal crayfish in both sampling years; n = 7); and (2) invaded (with signal crayfish) streams, comprising pre‐invaded (invaded before 2011; n = 8) and newly invaded (invaded between 2011 and 2018, n = 3). Despite similar habitat conditions in both years (all variables p > 0.05) fish and macroinvertebrate communities changed over time in pre‐invaded streams and by comparison to uninvaded streams. A decline in the abundance of benthic fish and YoY salmonids was observed in pre‐invaded and newly invaded streams. Complete disappearance of bullhead Cottus perifretum following signal crayfish invasion was recorded in two pre‐invaded streams. In the second study, S2, we assessed within‐stream differences in fishes and macroinvertebrates in two Tees streams by comparing sections with (invaded) and without (uninvaded) signal crayfish. Compared to uninvaded sections, taxonomic richness and abundance of fish and macroinvertebrates were significantly lower in invaded sections, and the overall communities also differed significantly. In S3, long‐term data series (since 1990) of water quality and macroinvertebrates of six Tees streams comprising those invaded by signal crayfish (n = 3) and uninvaded (n = 3) were analysed. Water quality showed little change, or an improvement, over time but significant changes in the macroinvertebrate taxonomic richness and community structure occurred following signal crayfish invasion. Long‐term changes in macroinvertebrate communities in invaded streams tended to be due to declines in more sedentary taxa such as molluscs and cased trichopterans. Widespread and long‐term ecological disruption is occurring because of signal crayfish invasion in upland streams of the Tees catchment that may lead to a complete disappearance of some benthic fish species, as well as reduced densities of YoY salmonids and a shift towards less diverse macroinvertebrate communities, dominated by more mobile, crayfish‐resistant taxa

Risking lives for living: a study on underwater fishing in the Padma River, Bangladesh

Different types of fishing methods and gears are being employed across the globe including Bangladesh. This study describes the underwater fishing method in the Padma River- one of the three largest rivers in Bangladesh. Standardised efforts have been made for collecting data of interest between September 2016 and May 2017. Two types of underwater fishing, with or without using oxygen cylinders, were recorded. Mean duration of fishing per effort was higher (by 382%) when fishermen used oxygen cylinders. Mean water depth of fishing sites was also higher when oxygen cylinders were used. Three species of finfish (Rita rita, Sperata seenghala and Labeo calbasu) and one freshwater prawn species (Macrobrachium dayanum) have been identified in the catch. The catch was dominated by M. dayanum in both fishing types (27 ± 9.3 [with oxygen] and 15 ± 5.2 [without oxygen]). However, all the number of caught fish species varied significantly among different sampling months in both fishing methods (P < 0.001) except L. calbasu in fishing with oxygen cylinder. A number of health issues of the fishermen were also recorded

Risking lives for living: a study on underwater fishing in the Padma River, Bangladesh

Different types of fishing methods and gears are being employed across the globe including Bangladesh. This study describes the underwater fishing method in the Padma River- one of the three largest rivers in Bangladesh. Standardised efforts have been made for collecting data of interest between September 2016 and May 2017. Two types of underwater fishing, with or without using oxygen cylinders, were recorded. Mean duration of fishing per effort was higher (by 382%) when fishermen used oxygen cylinders. Mean water depth of fishing sites was also higher when oxygen cylinders were used. Three species of finfish (Rita rita, Sperata seenghala and Labeo calbasu) and one freshwater prawn species (Macrobrachium dayanum) have been identified in the catch. The catch was dominated by M. dayanum in both fishing types (27 ± 9.3 [with oxygen] and 15 ± 5.2 [without oxygen]). However, all the number of caught fish species varied significantly among different sampling months in both fishing methods (P < 0.001) except L. calbasu in fishing with oxygen cylinder. A number of health issues of the fishermen were also recorded. Keywords: Fishing; Padma River; hand fishing; underwater fishing

Investigation of Phytoplankton and Physico-chemical Parameters in Nursery, Growout and Broodstock Ponds

The study measures the relationship between physicochemical variables with the cell density of phytoplankton in different stages of pond – nursery ponds, grow out ponds and brood stock ponds. The study was conducted on nine fish ponds as three from each category of pond at Natore Government Fish Farm in Bangladesh, during the months of January to June in 2012. The observed physicochemical variables– water temperature, transparency, dissolved oxygen, pH, ammonia-nitrogen, total alkalinity and total hardness – were found within the standard ranges. Four groups of phytoplankton– Bacillariophyceae, Chlorophyceae, Cyanophyceae and Euglenophyceae– werefound among the ponds where Euglenophyceae was recorded highest number almost in all ponds over the study period. Total abundance of different groups of phytoplankton was recorded as mean (±SD) cell density (cell/l) 62.77±2.16×104, 47.22±0.69×104, and 77.12±3.42×104 in nursery pond, grow out pond and brood stock pond, respectively. Overall phytoplankton was found better in brood stock pond than others. Total phytoplankton density has been exhibited significantly positive correlation with DO and inverse relation with water temperature, pH, ammonia-nitrogen and total alkalinity in case of nursery pond. In case of grow out pond, total phytoplankton density has been exhibited significantly positive correlation with temperature and transparency, and significantly negative correlation with others physicochemical characteristics. In case of brood stock pond, total phytoplankton density has no significant relationship with any physicochemical variables of water

Municipal wastewater can result in a dramatic decline in freshwater fishes: a lesson from a developing country

Impacts of ineffective wastewater management on the biodiversity of receiving waters in developing countries are poorly documented. Using a before-after-control-impact methodology, we measured the effects of untreated wastewater release on the fish community in the Barnoi River, Bangladesh. In 2006, prior to untreated wastewater discharge, fish abundance, species richness and water quality were similar across sampling sites. In 2016, after 8 years of wastewater release to the downstream reach, fish abundance and species richness were reduced by >47% and >35% respectively at downstream sites compared to unaffected upstream sites and >51% and >41% lower respectively compared to the pre-wastewater discharge period. The wastewater impact was particularly severe during months of low discharge (October–December). Water transparency, dissolved oxygen and pH were lower (P < 0.001) at impacted downstream sites compared to upstream sites. Nineteen species (41.3% of all species we recorded) are threatened in Bangladesh and the abundance of these species, except one, decreased significantly (P < 0.05) at the impacted sites. We recommend improved wastewater management by applying primary treatment facilities and incorporating reedbed filtration as a mean of biological treatment, into the canals carrying wastewaters. The success of such measures should be tested with fish species that were most responsive to wastewater, using the indicator species concept

Municipal wastewater can result in a dramatic decline in freshwater fishes: a lesson from a developing country

Impacts of ineffective wastewater management on the biodiversity of receiving waters in developing countries are poorly documented. Using a before-after-control-impact methodology, we measured the effects of untreated wastewater release on the fish community in the Barnoi River, Bangladesh. In 2006, prior to untreated wastewater discharge, fish abundance, species richness and water quality were similar across sampling sites. In 2016, after 8 years of wastewater release to the downstream reach, fish abundance and species richness were reduced by >47% and >35% respectively at downstream sites compared to unaffected upstream sites and >51% and >41% lower respectively compared to the pre-wastewater discharge period. The wastewater impact was particularly severe during months of low discharge (October–December). Water transparency, dissolved oxygen and pH were lower (P < 0.001) at impacted downstream sites compared to upstream sites. Nineteen species (41.3% of all species we recorded) are threatened in Bangladesh and the abundance of these species, except one, decreased significantly (P < 0.05) at the impacted sites. We recommend improved wastewater management by applying primary treatment facilities and incorporating reedbed filtration as a mean of biological treatment, into the canals carrying wastewaters. The success of such measures should be tested with fish species that were most responsive to wastewater, using the indicator species concept