Is current floodplain management a cause for concern for fish and bird conservation in Bangladesh’s largest wetland?

Worldwide, water regulatory structures have impacts on aquatic ecological connectivity. This study determined the effects of current sluice management on the fish community in the Baral River, a major connection to the largest wetland (Chalan Beel) in Bangladesh. It also examines wider problems for biodiversity conservation (particularly waterbirds) in that wetland, which has shrunk to 30% of its former dry-season size in 50 years. During the flood period, the peak breeding time for native floodplain fishes, sluices were in undershot operation (open by 16–60% of water depth). During this time, fish abundance and species richness were 229% and 155% higher respectively at sites upstream of the sluices, despite similar habitat upstream and downstream. Outside this period, when sluices were fully open, abundance and species richness were similar upstream and downstream. Fish samples were dominated by fry, which are susceptible to damage by sluices. Twenty (41.7%) of 48 fish species captured in this study are classed as threatened in Bangladesh and their abundance was significantly lower downstream of the sluices. Two alien species, Aristichthys nobilis and Hypophthalmichthys molitrix, were recorded, probably escapees from local aquaculture activities. Twenty-five species of wetland birds were recorded in the Chalan Beel. From interviews, 64% of these species appear to have decreased in the last 20 years, together with 11 more species that may have become locally extinct over this period. This suggests that widespread ecological disruption is occurring. Improved water management (e.g. gate opening height and duration) or modification (e.g. fish pass) of the Baral sluices is needed, to meet biodiversity and fisheries needs, rather than just for flood control and crop production. Improved hydrological and ecological connectivity and habitat protection are needed, as are a cessation of destructive fishing and seasonal fish ranching practices that currently provide synergistic pressures

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

Culture of mola (Amblypharyngodon mola) in polyculture with carps: experience from a field trial in Bangladesh

Studies were carried out during May 1997 to January 1998 in Kishoregani district in Bangladesh to investigate the production potential of carp polyculture in combination with Amblypharyngodon mola in seasonal ponds. The preliminary results indicate that A. mola can be successfully cultured in small seasonal ponds in polyculture with carp. This practice can result in an increase in the households' consumption of small fish which have a very high content of calcium, iron and vitamin A. In addition to the nutritional benefits, it can also provide additional income through sale of carp and surplus small fish

Environment and fish fauna of the Atrai River: global and local conservation perspective

The fish fauna of the Atrai River were studied for a period of two years from January 2011 to December 2012. Sampling was carried out by several fishing nets and traps on fortnight basis. A total of 74 fish species belonging to 27 families and 52 genera were recorded. Cyprinidae was the most dominant family contributing 18 species in 9 genera. Two alien species were found- Hypophthalmichthys molitrix and Hypostomus plecostomus. Thirty locally threatened species (Vulnerable 13.51%, Endangered 18.92% and Critically Endangered 8.11%) were recorded. But, no globally threatened species was found. Relative abundance of majority 36.49% species was rare. Global population trend of 24.32% recorded fish species was Declining. The highest number of species (42) was recorded in the November 2011. Whereas, the lowest the number of fish species (12) recorded in June and August 2011. Very high correlation was found between fish species and physical environmental parameters (air temperature, water temperature, and water transparency). This study concluded that Atrai River could be an excellent place for natural conservation of fish species. Nevertheless, efforts to maintain a sustainable fishing pressure, removal of existing alien species and avoiding further introduction of such species are recommended

Fish diversity of the River Choto Jamuna, Bangladesh: present status and conservation needs

River Choto Jamuna is an important and well-known river in north-west Bangladesh in terms of fish production and source of income for many fishermen living beside where this study has been conducted from January to December, 2012. This study revealed the existing fish species and their composition along with diversity, richness and evenness indices. A total of 63 species of fishes have been recorded belonging to 41 genera, 23 families and 9 orders. Cypriniformes was recorded as the most diversified fish group in terms of both number of species and individuals observed. Of all the fishes found, 41.27% species were threatened in Bangladesh including 15.87% vulnerable, 15.87% endangered and 9.52% critically endangered species. Overall values of diversity, richness and evenness indices were found to be 3.717, 6.954 and 0.897, respectively. Finally, considering all the findings, the establishment of fish sanctuaries to conserve available fish species, both threatened and non-threatened, naturally is recommended

Seasonal variation and community structure of fishes in the Mahananda River with special reference to conservation issues

This study was carried out in the Mahananda River from January to December 2013 with a view to determining the seasonal variation and community structure of fishes along with some conservation issues. Monthly sampling was carried out using traditional fishing gears and fishes were identified based on morphometric and meristic characters. A total of 4082 individuals of native fish species were captured, analyzed and classified into 62 species belonging to 46 genera, 25 families and 9 orders. Cypriniformes and Siluriformes were the dominant fish orders represented by 19 species each and the most abundant family was Cyprinidae (14 species). In addition to indigenous individuals, 9 individuals of 2 exotic fish species (Hypophthalmichthys molitrix and Pangasius hypophthalmus) were also recorded. Among three sampling sites, S-1 was the most diversified in terms of not only the number of individual fish but also the number of species present represented by mean (±SE) individuals of 151.50±25.22 and species of 25.58±3.91. Three distinct fish groups of fish families were revealed from the cluster analysis of similarity. To improve the situation, control of illegal fishing gears, establishment of sanctuaries and legal protection for threatened species are recommended

Fish diversity decline in the lower Gangetic plains: a victim of multiple stressors

Analysis of long-term data provides a valuable approach to determining the extent of biodiversity decline and likely causes, but such approaches are rare in large tropical rivers. We investigated the response of the fish fauna to hydrological, climate and anthropogenic factors over the period 1982–2017 in the lower Ganges (Padma) River, Bangladesh. Systematic effort-based sampling of fish between 2007 and 2017 from a 70-km reach showed a decreasing trend in abundance and diversity. Compared to 1982 data for the same sites and fishing methods, 28 fish species, including 16 nationally threatened ones, were absent in recent catches, suggesting local extinction of these. Fish community diversity was negatively affected by fishing pressure (71 fishermen in 1980, 2616 in 2019, 37.8-fold increase) and non-native species abundance (6.8-fold increase in abundance between 2007 and 2017). Permanent water area has reduced by ~ 50% since 1984. Annual mean rainfall, Ganges water depth and river discharge at the study location decreased significantly since 1980 (by 19.2%, 17.8% and 27.6% respectively, while annual air temperature increased (25.1 °C in 1981 to 26.2 °C in 2019). Water diversion at the Farakka Barrage, ~ 70 km upstream, is partially responsible for reductions in permanent water area in the study reach. Potential sources of biological invasion and water pollution have been identified. Widespread ecological consequences on fish diversity and productivity, resulting from multiple factors, are occurring in the lower Ganges. Reduction of fisheries impacts and improved prevention of accidental aquaculture releases of non-native fishes are identified as conservation priorities for arresting the decline of native fishes in the lower Ganges

Invasive vermiculated sailfin catfish (Pterygoplichthys disjunctivus) has an impact on highly valued native fish species

Invasion by armoured catfishes (Loricariidae) is a threat to native fish communities of warm, freshwater habitats. Following importation as an ornamental species, the vermiculated sailfin catfish Pterygoplichthys disjunctivus, has become established in inland waters of Bangladesh. We recorded the distribution of sailfin catfish in Bangladesh. Vermiculated sailfin catfish was recorded in 17 rivers across the majority of the country, with well-established breeding populations in four localities. We measured competition between three native carps and sailfin catfish by determining growth and survival, and by carrying out gut analysis. The competition experiment was carried out using a randomised block design in earthen ponds with similar physico-chemical parameters to freshwater habitats in Bangladesh. It demonstrated that growth and survival rate of native cyprinid fishes can be adversely impacted in the presence of sailfin catfish. In high-density catfish treatments, growth of Cirrhinus cirrhosus (bottom-feeding omnivore), Labeo rohita (midwater omnivore) and Catla catla (pelagic planktivore) was reduced by 48.4%, 21.4% and 2.4% respectively, compared to controls containing the three cyprinids but no catfish. Survival of C. cirrhosus reduced to 70% in high-density catfish treatments, compared to 100% in catfish-free ponds, with lesser effects on the other species. Low- and medium-density catfish treatments generated lesser growth and survival effects. Catfish diet remained stable across density treatments, but diet of native fishes deviated increasingly from control values as catfish density increased. This study demonstrates impacts of sailfin catfish on native fish species and the increasing distribution of sailfin catfish in Bangladesh

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