Expansion of aquaculture threatens the existence of wetlands in Bangladesh

Despite positive role of aquaculture in food production, the practice may impact the environment negatively and it is difficult to quantify the loss. In this study, we assessed land use changes in four important wetlands (Hardoho Beel, Angrar Beel, Shaoil Beel and Gopalpur Beel) of Bangladesh through analysis of historical satellite images (1990 – 2020) to show how expansion of aquaculture activities threatens the existence of freshwater wetlands. Since 1990, the water area of all four wetlands decreased significantly over time (all p < 0.001). Mean yearly loss of 47.9 ± 79.3 ha, 99.2 ± 185.5 ha, 51.2 ± 61.9 ha and 2.6 ± 4.7 ha were recorded for Hardoho Beel, Angrar Beel, Shaoil Beel and Gopalpur Beel respectively. A decreasing trend in wetland area was recorded in all wetlands, primarily due to excavation of aquaculture ponds. In 2020, aquaculture ponds represented 72% of the core wetland areas. Two wetlands (Hardoho and Gopalpur) were almost totally lost and converted to aquaculture ponds and agricultural lands. This study concludes that the existence of freshwater wetlands in Bangladesh is at stake and recommends further studies to determine its impacts on people's livelihood and biodiversity

Production and economics of carp polyculture in ponds stocked with wild and hatchery produced seeds

Lack of quality carp seeds is one of the major problems for fish production in Bangladesh. This experiment was conducted during July to December 2013 to study the production and economics of carp polyculture using wild and hatchery produced seeds in ponds in Faridpur district, Bangladesh.  Seeds of native major carps (NMCs) (Catla catla, Labeo rohita and Cirrhinus mrigala) and non-native carps (NNCs) (Hypophthalmichthys molitrix, Ctenophryngodon idella, Aristichthys nobilis and Cyprinus carpio) from four different sources were tested in feed and fertilizer based polyculture ponds under controlled mesocosm trials with four treatments (T1–T4), each with four replications. Combination, weight and density of the stocked species were same for all the treatments. Water quality parameters were monitored monthly and mean values were found within suitable range for fish farming. Mean final weight, weight gain, specific growth rate and yield of L. rohita, C. catla and C. mrigala were found significantly (P < 0.05) higher with treatment T1, T3 and T2 respectively. Treatments T1-T3 varied more significantly (P < 0.05) than treatment T4 for total fish yield and cost benefit ratio.  Polyculture of wild sourced NMCs and hatchery produced NNCs were found more profitable than aquaculture of hatchery produced NMCs and NNCs

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

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

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

Length-weight relationships and growth pattern of Macrobrachium malcolmsonii (H. Milne-Edwards, 1844) from the river Old Brahmaputra, Bangladesh

Study of biological parameters of a species is important for its sustainable management. The length-weight relationships and growth patterns of Macrobrachium malcolmsonii (H. Milne-Edwards, 1844), collected from the river Old Brahmaputra in Bangladesh, were determined in this study based on 359 specimens (carapace length, CL: 11–90 mm; body weight, BW: 0.2–54.4 g) including 308 male and 351 female individuals. For both sexes, intercepts, slopes, and coefficients of determinations of regression analyses between CL and BW varied monthly. The lowest values of intercept (–11.51 and –11.65 for male and female respectively) was recorded in October whereas the highest values were recorded in January for male (–7.01) and March for female (–8.26 for female). The minimum coefficient of determination was 0.784 (for male) and 0.801 (for female) whereas the maximum coefficient of determination was recorded 0.971 (for male) and 0.970 (for female). For male, the b value at 95% Cl revealed that the growth in March, June, July, September and February were isometric and in April, May, October, November and January were allometric. Whereas for female, the growth in March, April, June, July, November, January and February were isometric and was allometric in May, September and October

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