Reproductive biology of Lepidocephalichthys guntea: a key conservation approach considering environmental factors in Payra River, Bangladesh.

The guntea loach, Lepidocephalichthys guntea, is categorically common freshwater fish in Southeast Asia. Current study is the first elucidation on the reproductive feature of L. guntea including population structure, sex ratio (SR), size at first maturity (Lm), breeding period, and condition factor, emphasizing on the effect of environmental factors on reproduction of this fish in the Payra River (Southern Bangladesh) during July 2021 to June 2022. Using various conventional gears, 1128 individuals (534 males and 594 females) have been collected. Total length (TL), standard length (SL), and body weight (BW) of each fish were measured. Ovaries were cautiously dissected, removed, and precisely weighed. TL ranges from 4.6 to 9.7 cm (BW = 0.7-9.27 g) for male and 4.6-10.3 cm (BW = 0.8-10.75 g) for female. Both male (47.34%) and female (52.66%) populations were the leading group in 7.00-7.99 cm TL. Overall SR was not notably altered from anticipated value of 1:1 (male:female = 1:1.11). Nonetheless, monthly variations of SR specified females were considerably outnumbered males in each month excluding March-May. Lm range was 6.4-7.0 cm, so larger than Lm is recommended to exploit. Monthly changes in GSI indicated that the main spawning season was from March to June. The spawning season was substantially correlated with rainfall, nonetheless with temperature. Additionally, relative weight indicated that habitat was imbalanced with higher predators. A fishing ban is recommended during peak spawning to protect L. guntea in the Payra River and its surroundings based on current research.

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.

Evaluating biometric indices for Indian Gagata, Gagata cenia (Hamilton, 1822) through multi-model inferences.

Biometric indices provide crucial information on fish population growth and aquatic habitat well-being. This study offers the first comprehensive elucidation on biometric indices of Gagata cenia (Hamilton, 1822) specifically; population structure, growth pattern and parameters, form factor (a 3.0 ), conditions factors, prey-predator status, reproduction, optimum catchable length (L opt ), mortality and exploitation rate in the Jamuna River, northern Bangladesh. The aim of this study is to estimate stock status of G. cenia in order to protect the declining wild stock. Total of 725 fishes were randomly collected (ranges between 2.7 and 8.5 cm total length (TL), while 0.30-8.24 g body weight (BW)) occasionally using conventional fishing gears during June 2020 to May 2021. The b value of length-weight relationship (TL vs. BW) was 3.33 which indicated positive allometric growth pattern with r 2 value 0.942. Growth parameters were supposed as asymptotic length (L ∞ ) = 9.09 cm, (K) = 0.94 year-1, growth performance index (Ø') = 1.89 and longevity (t max ) = 3.2 year-1 for this population. The calculated a 3.0 was 0.0172 and Fulton's condition (K F ) is the best suited tool for assessing the well-being of this population. Additionally, relative weight (W R ) specifies an imbalanced territory with regard to the occurrence of predators. The size at sexual maturity (L m ) and L opt for combined sexes of G. cenia were 5.4 cm and 6.0 cm, respectively henceforth fish sizes 6.0-6.5 cm TL are recommended for exploitation. The current study verified fishing mortality was significantly lower than natural mortality and the exploitation rate (E) was 0.32 which indicated the stock was under fishing. Our findings would be very beneficial in planning the sustainable and appropriate management of this fish in Bangladesh and nearby 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 (Lm) and spawning season. According to the results of these indices, Lm 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 (FT) 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.

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 (Lm) and optimum catchable length (Lopt) 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 Lm and Lopt of these species from worldwide water bodies based on maximum length (Lmax). 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 Lm, three different models such as (i) empirical model based on Lmax, (ii) the relationship between TL (total length in cm) vs. GSI (gonadosomatic index in %), and (iii) logistic model were considered and Lopt was assessed based on L∞. The estimated lowest Lm was 11.8 cm (Lmax-based), 12.8 cm (TL vs. GSI), and 13.7 cm (logistic model) for Thryssa setirostris and highest Lm was 23.3, 20.5, and 22.0 cm for Priacanthus macracanthus through Lmax, TL vs. GSI, and logistic-based models, respectively. From these three models, the lowest mean value of Lm 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 Lopt 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 Lm and Lopt 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 (Lm) and optimum catchable length (Lopt).