Exploring the reproductive features of Clupisoma garua from Ganges River, Bangladesh: insights into eco-climatic factors for sustainable management and advancements in aquaculture practices

The Garua bacha, Clupisoma garua, holds considerable commercial and nutritional significance as a fish species. This study investigates the relationships between GSI (gonadosomatic index) and eco-climatic conditions, and provides comprehensive insights into several facets of reproduction, such as size at first sexual maturity (Lm), spawning season, peak spawning period, and proposes sustainable management strategies for C. garua in the Ganges River, northwestern, Bangladesh. Since January to December 2017, 570 female individuals have been gathered from the Ganges River using cast nets, gill nets, and square lift nets on a monthly basis. The total length (TL) of the specimens varied from 3.90 to 26.30 cm. Lm was estimated as 14.30 cm based on the results of the TL vs. GSI, MGSI (modified gonadosomatic index), DI (Dobriyal index), 14.00 cm through TL-FL regressions, and 15.18 cm depending on Lmax for this species. Furthermore, the spawning period was observed from May to August, peaking in June and July, based on greater GSI, MGSI, and DI values. Throughout the peak spawning season, there was not a significant differ from a value of 100 in the relative weight (WR) of the female species. During the spawning season, a substantial association between temperature and GSI (p = 0.0038); rainfall and GSI (p = 0.0043); DO and GSI (p = 0.0043); pH and GSI (p = 0.0002); and alkalinity and GSI (p = 0.0001) was detected. Analyzing a 55-year data series (1964-2018), it became clear that an increase in average air temperature of 0.0289 °C and a decrease in rainfall of 2.988 mm per year might possibly delay the spawning season of this species. As a consequence, the results of this study provide crucial information for developing management strategies to safeguard C. garua populations in the Ganges River and its adjacent ecosystems.

Assessing stocks of Mystus tengara (Hamilton, 1822) from three different management systems in Baors (Oxbow lake) of southwest Bangladesh: Implications for sustainable management

This study was conducted to observe the stock assessments of Tengara (Mystus tengara) in three different management systems of Baors (Oxbow lake) such as System-1, System-2, and System-3. In this study, 1806 specimens were sampled using traditional fishing nets to observe growth pattern, population structure, growth parameters, natural mortality (M), fishing mortality (F), total mortality (Z), recruitment pattern, exploitation rate (E), relative yield per-recruit (Y'/R), optimum catchable length, length at first capture, steady state biomass (SSB), and maximum sustainable yield (MSY) from January to December 2021. Digital slide calipers and a digital balance were used to measure each individual's total length (TL) and body weight (BW), respectively. An empirical maximum length-based model was used to calculate size at first sexual maturity (Lm), and optimum catchable length (Lopt) was calculated based on asymptotic length (L∞). The least square linear regression equation was used to determine the regression parameters. The value of regression parameter, 'b' was 3.01 for system-1, 2.78 for system-2, and 2.70 for system-3, indicating that growth pattern of Tengara is isometric in system-1, but negative allometric growth in system-2 and system-3. The highest asymptotic length (L∞) and weight (W∞) of Tengara were found in system-1 (11.19 cm and 13.67 g) in comparison with system-2, (10.98 cm and 12.49 g) and system-3 (9.09 cm and 6.96 g) respectively. The growth coefficient (K) of the von Bertalanffy growth function (VBGF) was 0.72 year-1, 0.72 year-1, and 0.73 year-1 for system-1, system-2 and system-3, respectively. The calculated M, F, Z were 1.72, 1.28, and 3.00 year-1 for system-1, 1.11, 0.67 and 1.78 year-1 for system-2 and 1.12, 0.84 and 1.96 year-1 for system-3 respectively. The calculated life span (tmax) was found 4.19 years for system-1, 4.15 years for system-2 and 4.12 years for system-3. The recruitment patterns showed that the highest relative percentage of recruits were found in July, June and September for system-1, system-2 and system-3 respectively, with the major recruitment peak occurring from April to June for system-1, May to June for system-2 and June to July for system-3. One minor recruitment peak also occurred from August to September in system-1. The exploitation rate was more or less same in all three systems indicating that Tengara is under exploited from all the Baors. The significantly highest SSB and MSY were found in system-1 (22.65 and 12.11 metric tons), compared to system-2 (16.16 and 10.28 metric tons) and system-3 (5.55 and 5.49 metric tons), respectively. Considering the values of regression parameters, recruitment pattern, SSB and MSY, system-1 was found more suitable for Tengara compared to system-2 and system-3 management practices of Baors. Finally, these findings will turn out to be paradigm for the impregnable management of Tengara in Baors of southwest Bangladesh.

Effect of water quality parameters and climatic influences on reproductive phenology of Macrognathus pancalus in wetland ecosystem: recommending a long-term management approach and conservation policy

The study conducted an investigation into the reproductive biology of M. pancalus and assessed the influence of water quality parameters and environmental factors on the spawning pattern within the Gajner Beel ecosystem in Bangladesh. A total of 1218 individuals of M. pancalus (46.39% males and 53.61% females) were collected monthly from the Gajner Beel during January to December 2018 using various fishing gears. The total length (TL) of each individual was measured using digital slide calipers, and the whole body weight (BW) was measured using an electronic balance. Fulton's conditions factor (KF) showed significant differences between males and females. The calculated Lm were 11.11 cm, 11.30 cm, and 11.10 cm based on maximum length, gonadosomatic index (GSI), and the logistic model. The spawning season extended from May through August, with June and July being peak months. The average total fecundity was 1495.52 ± 840.24, with a range of 370 to 4069. During peak spawning season, the average temperature and rainfall were 27°C and 370 mm, respectively. Rainfall, dissolved oxygen, total alkalinity, and pH all had a significant (p < 0.01) positive effect whereas temperature and TDS all had a significant (p > 0.01) negative effect on GSI. Annual air temperature in the study area increased by 0.053 °C/year, with a regression coefficient value (r2 = 0.1695), while annual mean rainfall decreased by 5.97mm/year (r2 = 0.076). This research will contribute to the development of conservation and management approaches of Mastacembelidae fish in relation to current climate variability in sub-tropical waters.

Species identification, reproductive biology, and nutritional value of marine shellfish (Meretrix lyrata) in the Bay of Bengal

Meretrix lyrata which is under the family of Veneridae and under the order of Venerida, is a nutritionally and economically important edible mussel in Bangladesh. However, studies on species identification and nutritional value in M. lyrata are scarce. Therefore, a detailed investigation was conducted on (i) species identification of the common edible mussel through DNA-barcoding and morphometrics, (ii) reproductive features, such as size at sexual maturity, spawning, and peak-spawning seasons under different environmental factors, and (iii) nutritional status through proximate analysis of M. lyrata mussel collected from the Bay of Bengal, Bangladesh. The results indicated that the size at sexual maturity for M. lyrata was 4.2 cm and the spawning seasons were significantly affected by the dissolve oxygen and salinity. The study also demonstrated that the spawning of M. lyrata occurred from January to June and December while peak spawning season was May in the Bay of Bengal. The higher protein and moisture contents with lower fat in M. lyrata indicated that are value-added seafood with higher nutritional values for consumers.

Occurrences, sources, fate and impacts of plastic on aquatic organisms and human health in global perspectives: What Bangladesh can do in future?

Bangladesh is not an exception to the growing global environmental problem of plastic pollution. Plastics have been deemed a blessing for today's world thanks to their inexpensive production costs, low weight, toughness, and flexibility, but poor biodegradability and massive misuse of plastics are to blame for widespread contamination of the environmental components. Plastic as well as microplastic pollution and its adverse consequences have attracted significant investigative attention all over the world. Plastic pollution is a rising concern in Bangladesh, but scientific studies, data, and related information are very scarce in numerous areas of the plastic pollution problem. The current study examined the effects of plastic and microplastic pollution on the environment and human health, and it examined Bangladesh's existing knowledge of plastic pollution in aquatic ecosystems in light of the rapidly expanding international research in this field. We also made an effort to investigate the current shortcomings in Bangladesh's assessment of plastic pollution. This study proposed several management approaches to the persistent plastic pollution problem by analyzing studies from industrialized and emerging countries. Finally, this work pushed investigators to investigate Bangladesh's plastic contamination thoroughly and develop guidelines and policies to address the issue.

Wildfires in Australia: a bibliometric analysis and a glimpse on 'Black Summer' (2019/2020) disaster

A wildfire, an unplanned fire that is mainly uncontrolled and originates in combustible vegetation in rural or urban settings, is one of the most pervasive natural catastrophes in some areas, such as Siberia, California and Australia. Many studies, such as standard reviews, have been undertaken to look into the works of literature on wildfires or forest fires and their effects on aquatic and terrestrial ecosystems. Regrettably, conventional literature reviews failed to identify the important researchers, evolving complexities, emerging research hotspots, trends and opportunities for further research on the ground of wildfire study. The present study employs bibliometric analysis to investigate this study area qualitatively and quantitatively. The Scopus database systems and Web of Science Core Collection yielded 78 qualifying papers, which were then evaluated using Biblioshiny (A bibliometrix tool of R-studio). According to the statistics, the discipline is expanding at a pace that is 13.68% faster than average. So far, three key periods of transformation have been documented: preliminary evolution (8 articles; 1999-2005), gentle evolution (14 articles; 2006-2013) and quick evolution (56 articles; 2014 to 2021). Forest Ecology and Management and Science journals have the highest number of publications, accounting for 7.70% of total wildfire-related articles published from 1999 to 2021. However, recent data indicate that investigators are shifting their focus to wildfires, with the term 'Australia' having the highest frequency (91) and 'wildfire' having the second highest (58) as the most appeared keywords. The present study will provide a foundation for future research on wildfire incidence and management by receiving information by synthesising previously published literature in Australia and around the world.

Assessment of Stock Status, Metal Contents with Human Health Risk of Gudusia chapra from Oxbow lake, Bangladesh

The current study is focused on a comprehensive stock assessment of Gudusia chapra to assess the stock status along with feeding habits, essential minerals content and risk to human health from exposure to heavy metals. A total of 723 specimens from the Bukvora Baor, Bangladesh were used to estimate the total body length (TL) and body weight (W) which ranged from 5.5 to 14.5 cm and 1.62-26.45 g, respectively. The estimated asymptotic length (L _∞) of this species (15.38) was in comparison with average length at 10 cm from 723 specimens along with the rate of 0.70 yr^-1 for approaching to asymptotic length. The obtained growth performance index (φ) 2.2 indicates that this species is not economically feasible to bring under aquaculture. At an average annual water surface temperature of 28 °C, natural mortality, 1.71yr^-1 indicating good ecological suitability of Bukvora oxbow lake (Baor). The estimated current exploitation ratio (0.24) reflected under-exploitation status with total instantaneous mortality (2.25 years^-1) and fishing mortality (0.55 years^-1). The recruitment pattern of this species was observed across the year, with main peak occurring during the period of April to May. The estimated total steady state biomass (3.91 metric ton) and MSY (4.40 metric ton) based on length-structured virtual population analysis (VPA) length-structured virtual population analysis (VPA) through FiSAT II schedule indicating the sustainable production of this species. The obtained values of proximate compositions (% of protein, fat, Moisture, ash) showed no significant variations during different seasons throughout the year. The monthly measurements of GaSI showed significant alterations (p < 0.05). The value of essential minerals (Na and Ca) was recorded 9.18 mg and 245.19 mg per 100 g of fish flesh, respectively. Target hazard quotient and Cancer risk for all detected heavy metals were far below the recommended levels by United States Environmental Protection Agency. Therefore, the target fish species from oxbow lake is safe and have no human health risk. Therefore, the outcomes of this research would be very worthwhile in carrying out specific management for G. chapra in Baor ecosystems.

Are there any effects of eco-climatic factors on freshwater prawn reproduction: a study on monsoon river prawn, Macrobrachium malcolmsonii

Prawns are regarded as delicious food items and a source of income as it is the salient exportable fishery item of Bangladesh and a number of other countries. Climate change may inhibit the general physiological activity of prawns. This study explored the eco-climatic effects on reproduction, including size at first sexual maturity (L_m), spawning season, and fecundity of monsoon river prawn, Macrobrachium malcolmsonii (Milne-Edwards, 1844). The study was carried out in the Ganges (Padma) River basin, northwestern Bangladesh, from January to December 2014. Seven hundred fifty-seven specimens ranging from 0.80 to 18.27 g BW (body weight) with TLs (total length) of 4.20 to 11.52 cm were analyzed. The L_m was estimated as 6.2-6.6 cm. Total fecundity was higher than earlier studies and ranged from 2743 to 122,165 with a mean value of 6715 ± 2437. The spawning season was estimated from April to October with a peak in July. Significant correlation was found between rainfall and the presence of ovigerous females, i.e., spawning season. The number of ovigerous females increased in ≥ 100 mm average rainfall, and the maximum ovigerous female spawned at 250-320 mm rainfall. Spawning season of M. malcolmsonii may have shifted with shifting rainy season as a result of climate change. The findings of our investigation would be useful for sustainable management of the fishery of M. malcolmsonii and other prawn species in the Ganges River, Bangladesh, and adjoining countries with similar eco-climatic factors.

Reproductive aspects of Anabas testudineus collected from the Gajner Beel wetland in Bangladesh: implications for its conservation under changing eco-climatic conditions and suggestions for best aquaculture practice

The freshwater climbing perch, Anabas testudineus, is an economically and nutritionally valuable food fish. This study explores the various reproductive contents (size at sexual maturity, reproductive period and fecundity) of A. testudineus in the Gajner Beel concerning the eco-climatic variabilities and suggests sustainable management policies. A total of 709 individuals were randomly collected from January to December 2019 among 371 females that were sorted out for this study. Total length (TL) ranged from 7.50 to 16.40 cm. Based on the maximum length (L_max), TL vs. gonadosomatic index (GSI), TL-standard length (SL) regression and logistic model, the size at sexual maturity (L_m) was 10.00 cm, 10.40 cm, 11.00 cm and 11.50 cm, respectively. The spawning season was May to August and peaked in June-July. The Fulton's condition (K_F) was suggested as the best condition factor (p < 0.0001), and relative weight (W_R) showed no significant difference from 100 for females (p = 0.143). Fecundity was ranged from 9459 to 35,915. A significant relationship was observed between GSI and temperature (p = 0.0016), dissolved oxygen (DO) (p < 0.0001), pH (p < 0.0001), alkalinity (p < 0.001) and climatic parameters (air temperature, p < 0.001 and rainfall, p < 0.001). The data series of 48 years (1971-2019) revealed that the rise of average air temperature by 0.029 °C and the reduction of rainfall by 2.96 mm per year might shift the spawning season of A. testudineus 15-20 later. Therefore, this study will be helpful for the sustainable management and conservation of the wild stocks of A. testudineus in the Gajner Beel and adjoining ecosystems.

Reproductive performance of Asian stinging catfish Heteropneustes fossilis (Bloch 1794) in the Ganges River (NW Bangladesh) in relation to environmental factors

Reproduction plays an important role in fish population efficiency and its resiliency to fishing and environment changes. The present study described the comprehensive information on reproductive feature of stinging catfish, Heteropneustes fossilis (Bloch 1794), including size at sexual maturity, spawning season, and fecundity using 622 female individuals sampling by the use of gill net, cast net, and square lift net from January to December 2019 in the Ganges River. We calculated the influences of various environmental parameters which include temperature, dissolved oxygen, pH, and rainfall on the reproductive feature of H. fossilis in the Ganges River. For every specimen, total length (TL), standard length (SL), and body weight (BW) were estimated by measuring board and electronic weighing scale. With ventral dissection of fishes, female gonads were cautiously removed and measured to 0.01 g precision. The gonadosomatic index (GSI), modified gonadosomatic index (MGSI), and Dobriyal index (DI) were used to assess the size at sexual maturity (L_m) and spawning season. According to the results of these indices, L_m was obtained 15.5 cm in TL. Also, TL₅₀ was determined through logistic function as 15.5 cm in TL. Moreover, the highest GSI, MGSI, and DI values indicated the spawning season as of March-August, with peak in May-June. Total fecundity (F_T) varied from 2059 to 59,984 with a mean of 25,028 ± 15,048. Temperature and rainfall was statistically correlated with GSI. In addition, long climatic data series analysis denoted that yearly mean atmospheric temperature is rising in 0.028 °C/year and yearly mean rainfall is declining in 2.98 mm/year which may suggest a potential shift of the spawning period of the species in the future if this trend persists. The results of our study might be more useful in imposing particular management and conservation for H. fossilis in the Ganges River and the surroundings.

Life history traits of Mystus vittatus in the Ganges River, Bangladesh: recommendation for its sustainable management considering climate change

Freshwater catfishes are regarded primarily as a source of food and sport, so they are highly valuable economically. We comprehensively studied life history features of Mystus vittatus, including sex ratio (SR), population structure, growth pattern, condition, form factor (a_3.0), sexual maturity (L_m), spawning season, fecundity, mortality (i.e., total mortality (Z), natural-mortality (M_W), and fishing mortality (F)), optimum catchable length (L_opt), length at first capture (L_c), and environmental factors (temperature and rainfall) with management policies from the Ganges River during July 2017 to June 2018. SR (1:1.48) differed noticeably from the expected 1:1 ratio (p < 0.05). Total length (TL) ranged from 6.80-16.00 cm for males and 6.53-18.80 cm for females. The growth was negative allometric for both sexes. Fulton's condition factor was the best one and mean relative weight showed no significant difference from 100 for both sexes that indicates balanced population. L_m was 9.60, 9.70, and 8.80 cm based on the gonadosomatic index (GSI), logistic, and maximum length (L_max), respectively. Spawning season was April to September and the peak was May to July. Fecundity varied from 5942 to 49,852 (mean ± SD, 11,898 ± 5028) and a positively correlated with TL and BW. Z was 1.80 year^-1, M_w was 0.97 year^-1, and F was 0.83 year^-1. L_opt was 11.14 cm (TL) and L_c was ~ 8.47 cm (TL). Temperature and rainfall both were significantly related with GSI and suitable range of temperature and rainfall for spawning of M. vittatus was 28-34 °C and 200-390 mm, respectively. Long data series pointed that average air temperature was increasing and rainfall was decreasing. By considering all of the above parameters, we can take the proper management actions for M. vittatus and other freshwater catfishes on the Indian sub-continent, to ensure long-term self-sustainability and sustainable harvest for the benefit of fishers and communities.

Life-history traits of ten commercially important small indigenous fish species (SIFS) in the Oxbow lake (Southwestern Bangladesh): key for sound management

For the first time, we revealed the life-history traits including growth pattern (length-weight relationships, LWRs), condition factors, form factor (a_3.0), first sexual maturity (L_m), age at first sexual maturity (t_m), life span (t_max), natural mortality (M_w), asymptotic length (L_∞), and optimum catchable length (L_opt) of ten commercially important small indigenous fish species (SIFS) in the Oxbow lake (Baor), southwestern regions of Bangladesh. A total of 1651 specimens were sampled during January to December 2020 with traditional fishing gears including seine nets, gill nets, and lift nets. Individual total length (TL) and body weight (BW) were measured by digital slide calipers and digital balance, respectively. To calculate the L_m, empirical maximum length-based model was considered, and L_opt was calculated based on L_∞. The TL vs. BW relationship indicated positive allometric growth for Chanda nama (Hamilton 1822), Channa punctata (Bloch 1793), Channa striata (Bloch 1793), Lepidocephalichthys guntea (Hamilton 1822), Macrognathus pancalus (Hamilton 1822), and Puntius sophore (Hamilton 1822), but negative allometric growth for Badis badis (Hamilton 1822), Gudusia chapra (Hamilton 1822), Glossogobius giuris (Hamilton 1822), and Hyporhamphus limbatus (Valenciennes, 1847). All r² values exceed 0.910 that indicated all LWRs were highly significant (P < 0.001). According to Spearman correlation test, Fulton's condition factor (K_F) vs. BW was highly correlated (P < 0.001), indicating better well-being for these species. Moreover, a_3.0 indicates B. badis, C. punctata, C. striata, G. giuris, H. limbatus, L. guntea were elongated; C. nama, P. sophore, were short and deep; G. chapra was fusiform, and M. pancalus was eel-like body shape respectively. The minimum t_m and t_max were obtained as 0.74 year and 2.66 year for C. striata and maximum were 0.93 year and 3.31 year for B. badis, respectively. This study provided information on t_m and t_max for ten SIFS that is globally absent. From empirical models, the smallest mean value of L_m was found for B. badis (3.98 cm), and the greatest was found for C. striata (16.96 cm). The minimum L_opt was obtained as 3.78 cm TL for B. badis and maximum was 14.09 cm TL for C. punctata. The minimum M_w was documented as 1.39 for B. badis and maximum was 1.73 for C. striata. The output of this research will be helpful for developing sustainable management policies and protection of SIFS through the application of mesh size based on L_m and L_opt in the Oxbow lakes, Bangladesh and neighboring countries.

Assessing the exploitation status of main catfish Eutropiichthys vacha based on length based stock assessment models in the Kaptai Lake from Bangladesh

The current study focuses on the detailed data on stock assessments including population structure, growth parameters, mortality, recruitment pattern, exploitation rate (E), maximum sustainable yield (MSY) and relative yield per-recruit of Eutropiichthys vacha (Hamilton, 1822) based on 2512 specimens through regular monthly sampling using gill net, cast net, and square lift net in the Kaptai Lake, located in the hilly region of Bangladesh during January to December 2017. Total length (TL) and body weight (BW) were measured using digital slide calipers and electronic balance with 0.01 cm and 0.01g accuracy for each individual. The asymptotic length (L_∞) was 44.40 cm and growth coefficient (K) was 0.70 year⁻¹. The growth performance index (Ø′) was 3.14. The age at zero length (t₀) was 0.027 year and life-span (t_max) was 2.73 year. We estimated total mortality (Z), natural mortality (M) and fishing mortality (F) as 4.23, 1.27 and 2.96 year⁻¹, respectively. The recruitment pattern was throughout the year with two pick-events during May and September. Length at first capture (L_c) was 20.65 cm TL. The E was 0.70 where the E_max (exploitation rate producing maximum yield) was 0.45 which indicates 25% over fishing. The MSY was estimated as 34257 metric ton. In conclusion, the results of this study would be very operative to execute specific management for E. vacha in Kaptai Lake, Hilly region of Bangladesh.

Effects of COVID-19 pandemic on Baor (Oxbow lake) fisheries: Decreased economic livelihoods and food security

The COVID-19 pandemic has had a negative impact on the global economy, with Bangladesh as a developing country exhibiting greater vulnerability. This pandemic has negatively affected the livelihoods and food security of the nation. Baor (oxbow lake) fisheries communities also were significantly affected during the pandemic, in terms of incomes, food security, health conditions, etc. Fishers have had to stop harvesting, or lower the quantity, of fishes, the sale of which was the main income source of the baor fishers' community because of reduced consumer demands during the lockdown conditions. The supply chains of fishes and fish culture inputs were also disrupted because of a lack of needed transportation, thereby hindering the availability of this convenient protein source from the fish. All these factors negatively impacted the incomes of the people dependent on this important fishery. If appropriate measures are applied to overcome these various difficulties, the baor fisheries may again contribute significantly to the livelihoods and food security of the population in the southwestern part of Bangladesh.

Stock assessment of Hooghly Croaker Panna heterolepis in the Bay of Bengal (Southern Bangladesh): implications for sustainable management

The study describes growth pattern, growth parameter, mortality, recruitment pattern, exploitation rate (E) and maximum sustainable yield (MSY) to Panna heterolepis from the Bay of Bengal (Bangladesh). About 1223 specimens were collected from commercial fishermen for 12 consecutive months from January to December, 2019. Length–frequency data were analyzed with FAO-ICLARM Stock Assessment Tool. Moreover, our study recorded different water quality and environmental parameters including pH, rainfall, temperature and DO (dissolved oxygen) from the Bay of Bengal. The findings of the study revealed that the allometric co-efficient (b) value indicated negative allometric growth (<3.00) for P. heterolepis population. Whereas, the population dynamic parameters showed growth coefficient (K) 0.13 year⁻¹, life-span (t_max) 3.85 year and growth performance index (Ø′) 2.30. Along with this, P. heterolepis was found to grow rapidly with an asymptotic length (L_∞) of 39.08 cm. We found that the natural mortality (M =0.44 year⁻¹) rate was almost similar with fishing mortality (F = 0.42 year⁻¹). Consequently, the standing stock was not quite sustainable with the existing fishing strategy. Furthermore, the maximum allowable exploitation rate (E_max= 0.471) was lower than the recorded exploitation rate (E = 0.490). Subsequently, overfishing is the most focal threat to the wild stock. The recruitment pattern was almost continuous throughout sampling period. Finally, the MSY was assessed at 10234.47 metric tons. Additionally, the environmental parameters denoted that the ecosystem was in a balanced condition for the wild population. The findings would be very useful to introduce appropriate fishing regulations in the Bay of Bengal and nearby ecosystem.

First record on size at sexual maturity and optimum catchable length of 10 marine fishes from the Bay of Bengal (Bangladesh) through multi-models approach: a key for sound fisheries management

Appropriate management systems for the protection of fishes are mostly relying on the information of size at sexual maturity and optimum catchable length. The purpose of this research was to estimate the size at sexual maturity (L_m) and optimum catchable length (L_opt) of 10 marine fish species from the Bay of Bengal (Bangladesh) through multi-models using commercial catches from October 2019 to September 2020. Also, we calculated the L_m and L_opt of these species from worldwide water bodies based on maximum length (L_max). A total of 2967 specimens of 10 fish species were evaluated in the current study and total length (TL) was noted up to 0.1 cm using a measuring board, while body weight (BW) and gonad weight (GW) are weighed by digital electronic balance with 0.01 g accuracy. To assess the L_m, three different models such as (i) empirical model based on L_max, (ii) the relationship between TL (total length in cm) vs. GSI (gonadosomatic index in %), and (iii) logistic model were considered and L_opt was assessed based on L_∞. The estimated lowest L_m was 11.8 cm (L_max-based), 12.8 cm (TL vs. GSI), and 13.7 cm (logistic model) for Thryssa setirostris and highest L_m was 23.3, 20.5, and 22.0 cm for Priacanthus macracanthus through L_max, TL vs. GSI, and logistic-based models, respectively. From these three models, the lowest mean value of L_m was obtained for T. setirostris (12.7 cm) and highest was recorded for P. macracanthus (21.9 cm). Fifty percent of mature marine species was in 14.9 cm TL and 90% species was in 19.5 cm TL. The smallest L_opt was obtained as 13.4 cm TL for T. setirostris and largest was 28.2 cm TL for P. macracanthus. This study was generated data on L_m and L_opt for 10 newly marine species, which are globally absent. Therefore, this study will be helpful for developing sustainable management strategies and conservation of marine fishes through the implementation of mesh size based on the size at sexual maturity (L_m) and optimum catchable length (L_opt).

First report on reproductive features of the Hooghly croaker Panna heterolepis Trewavas, 1977 from the Bay of Bengal in relation to environmental factors

This study highlights the reproductive biology of Hooghly Croaker, Panna heterolepis Trewavas, 1977 which is one of the dominant fish in the Bay of Bengal (Bangladesh) based on monthly sampling of 569 female individuals from January to December 2019. We observed the effect of different environmental factors (temperature, rainfall, dissolved oxygen, and pH) on the reproduction of P. heterolepis. Measurements of each individual like total length (TL) and body weight (BW) were taken by using of measuring board and digital balance. Gonads were carefully removed through ventral dissection from females and weighed to 0.01 g accuracy. To assess the size at sexual maturity (Lm), spawning season, and its peak, the GSI (gonadosomatic index in %), MGSI (modified gonadosomatic index in %), and DI (Dobriyal index) were considered. Based on these indices, the Lm was documented 15.0 cm in TL. Moreover, L50 was predicted by logistic calculation as 15.0 cm TL. Furthermore, greater values of GSI, MGSI, and DI values denoted the spawning season as of January to July, with a peak in February. Additionally, Fulton's condition factor (KF) was significantly correlated with GSI values. In addition, GSI was statistically correlated with temperature. However, other environmental factors (rainfall, dissolved oxygen, and pH) did not show any significant relation with GSI. Finally, the outcomes of our study might be useful to carry out specific management programs for P. heterolepis in the Bay of Bengal and nearby aquatic ecosystem.

Reproduction of Eutropiichthys vacha (Schilbeidae) in the Ganges River (NW Bangladesh) with special reference to potential influence of climate variability

The Batchwa vacha, Eutropiichthys vacha is commercially important, supporting a viable small- and large-scale fishery throughout the Ganges River, NW Bangladesh. This study provides detail information on reproduction of E. vacha including size at sexual maturity, spawning and peak spawning season, and fecundity based on 734 female specimens through regular monthly sampling using cast net, gill net, and square lift net in the Ganges River during January to December 2016. Also, our study estimated the effects of climate change including temperature and rainfall on reproduction of E. vacha in the Ganges River. For each individual, lengths (total length, TL; standard length, SL) and body weight (BW) were measured with slide caliper and digital balance, respectively. Gonads (ovaries) were collected carefully by ventral dissection of each female specimen and weighed to the nearest 0.01 g accuracy. The gonadosomatic index (GSI % = (GW/BW) ×100), modified gonadosomatic index (MGSI % = (GW/BW - GW) × 100), and Dobriyal index (DI = [Formula: see text]) were calculated to estimate the size at sexual maturity (L₅₀) and spawning season. Based on GSI, MGSI, and DI, the L₅₀ was calculated as 12.5 cm TL for female. The TL₅₀, the TL at which 50% of individuals become mature, was calculated by logistic equation as 12.7 cm. Also, on the basis of higher values of GSI, MGSI, and DI, spawning season was ranged from April to August, with the peak in June-July, signifying the peak spawning season for E. vacha in the Ganges River. The total fecundity (F_T) ranged from 4800 to 77,976 (mean ± SD, 31384 ± 23,747) and was highly correlated with TL and BW. Water temperature during the spawning period ranged from 28 to 34 °C, with an average of 31 °C and there was significant correlation between temperature and GSI. Also, the spawning season coincides with the peak rainfall and there was significant correlation between rainfall and GSI. Additionally, analysis of long data series indicated that annual average air temperature is increasing by 0.0258 °C/year, while the annual average rainfall is decreasing by 3.107 mm/year. Finally, the findings of this study would be very effective to impose specific management for E. vacha in the Ganges River and surrounding ecosystems.

A comparison between ice and salt storages on bacteriological quality of Asian seabass (Lates calcarifer)

The study compares the bacteriological quality on Asian seabass (Lates calcarifer) between ice and salt storage methods. The main objectives of the study were to identify different bacteria constituents and quantitative bacterial load in Asian seabass when preserved with ice and sea salt. For the purpose of this study, Asian seabass was stored in two different conditions of ice-chilled and salted for 2 days. All fish samples were analyzed by performing bacteriological analysis and the isolated bacteria were identified by using API identification system. In case of the quantity of bacteria in the flesh, Chilling and salting had no significant difference to the quantity of bacteria on fish flesh. As for the skin, salt-preserved fish showed higher quantity of bacteria than ice-preserved fish. Acinetobacter baumannii and Pseudomonas fluorescens had been identified from skin sample of ice-chilled fish. Besides P. fluorescens and A. baumannii other isolates identified include Vibrio and Myxobacteria. All bacteria were cocci-shaped except a few bacilli. In term of bacteria number and morphological characteristics, ice-chilled preserved fish was better than salt preserved fish. Overall, less number of bacteria was observed in both ice-chilled and sea salt preserved fish. The result of this study indicated that the quick preservation is a very important factor to control bacterial load in the preserved fish.

Effects of iso-nutrient fertilization on plankton production in earthen ponds of Bangladesh

The experiment was conducted to evaluate the effects of iso-nutrients fertilization on fertilizer combinations, containing a similar amount of nitrogen (N) and phosphorus (P) were the production of plankton in earthen ponds for a period of eight weeks. Two different were tested in triplicate using six earthen ponds of 100 m2 each. The fertilizer combinations of cow manure, urea and Triple Super Phosphate (TSP) at the rate 5000, 125 and 100 kg ha(-1), respectively, containing approximately 102 kg N and 65 kg P was used for treatment-1 (T-l). Another combination of poultry-manure, urea and TSP at the rate of 2000, 125 and 100 kg ha(-1), respectively, was considered as the treatment-2 (T-2). The application rate of poultry manure was adjusted to make the nutrient (N and P) content of fertilizer combination in T-2 similar to that in T-1. Four groups of phytoplankton namely, Bacillariophyceae, Chlorophyceae, Cyanophyceae and Euglenophyceae and two groups of zooplankton namely, Crustacea and Rotifera were identified. The mean abundance of both phytoplankton (78.25 +/- 6.33 x 10(4) cells L(-1)) and zooplankton (57.63 +/- 4.59 x 10(4) cells L(-1)), were significantly higher (p < 0.05) in earthen ponds which treated with poultry manure. The result showed that despite iso-nutrients content, the nutrient status of poultry manure proved to be superior to cow manure.

A preliminary observation on water quality and plankton of an earthen fish pond in Bangladesh: recommendations for future studies

The present study provides a characterization of water quality and plankton samples in earthen fish pond in Rajshahi, Bangladesh. Sampling was done over a period of six months, running from October, 2004 through March, 2005. All the water quality parameters were within the optimal ranges for plankton productivity. Temperatures varied from 19.75 to 27.25 degrees C; transparency, 24.75-29.50 cm; pH, 6.62-7.85; Dissolved Oxygen (DO), 3.87-5.85 mg L(-1); free CO2 5.25-7.25 mg L(-1) and bicarbonate (HCO3) alkalinity, 81.25-147.5 mg L(-1). Analyses of plankton samples recorded a total of 5 classes phytoplankton viz.; Bacillariophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Euglenophyceae and 2 classes of zooplankton; Crustacea and Rotifera. The phytoplankton population was comprised of 17 genera belonging to Cyanophyceae (5 classes, 34.47%), Bacillariophyceae (3, 13.87%), Cyanophyceae (3, 34.48%), Euglenophyceae (3, 10.68%) and 1 to Dinophyceae (6.50%). The zooplankton population consisted of 10 genera belonging to Rotifera (4, 40.13%) and Crustacea (6, 59.87%). Phytoplankton and zooplankton abundance varied from 60800 to 239400 units/l and 7620 to 12160 units/l, respectively. It is concluded that the phytoplankton groups provide the main support for earthen pond aquaculture in the pond compared to zooplankton classes. The information provides for more research to compare water quality and pond plankton characteristics in earthen aquaculture systems with and without fish stocking. Further studies on the seasonal changes of water quality parameters and its effects on plankton production in the fish ponds and all year extended monitoring is recommended in future studies.