Some biological aspects of chacunda gizzard shad, Anodontostoma chacunda (Hamilton, 1822) from the Bay of Bengal, Bangladesh.

Anodontostoma chacunda is a commercial fish species in the market and is usually consumed in fresh, smoked, and dried forms. This study investigated the population structure, length-weight relationships (LWR), condition factor (K F ), size at sexual maturity (L m ), and breeding season of A. chacunda in the Bay of Bengal, Bangladesh, using the data collected from January to December 2020. A total of 1061 individuals were collected in the sampling period with the help of fishers. Total length (TL) and body weight (BW) were measured using a measuring board and an electronic balance. The TL ranged from 12.50 to 26.70 cm. The allometric coefficient (b) value was 3.34, indicating positive allometric growth in this species. The fish is in good condition, evidenced by its condition factor (K F ) ranging between 0.88 and 1.73. Maturity size ranged from 15.40 to 16.80 cm (TL) based on three distinguished models. Spawning time lasts from January to May and from September to December. The peak spawning time was December of A. chacunda in the Bay of Bengal. This information could prove valuable for fisheries researchers and biologists, facilitating efforts toward the conservation and sustainable management of this species.

Power Scavenging Microsystem for Smart Contact Lenses.

On-the-eye microsystems such as smart contacts for vision correction, health monitoring, drug delivery, and displaying information represent a new emerging class of low-profile (≤ 1 mm) wireless microsystems that conform to the curvature of the eyeball surface. The implementation of suitable low-profile power sources for eye-based microsystems on curved substrates is a major technical challenge addressed in this paper. The fabrication and characterization of a hybrid energy generation unit composed of a flexible silicon solar cell and eye-blinking activated Mg-O2 metal-air harvester capable of sustainably supplying electrical power to smart ocular devices are reported. The encapsulated photovoltaic device provides a DC output with a power density of 42.4 µW cm-2 and 2.5 mW cm-2 under indoor and outdoor lighting conditions, respectively. The eye-blinking activated Mg-air harvester delivers pulsed power output with a maximum power density of 1.3 mW cm-2. A power management circuit with an integrated 11 mF supercapacitor is used to convert the harvesters' pulsed voltages to DC, boost up the voltages, and continuously deliver ≈150 µW at a stable 3.3 V DC output. Uniquely, in contrast to wireless power transfer, the power pack continuously generates electric power and does not require any type of external accessories for operation.

Metasurface supporting quasi-BIC for optical trapping and Raman-spectroscopy of biological nanoparticles.

Optical trapping combined with Raman spectroscopy have opened new possibilities for analyzing biological nanoparticles. Conventional optical tweezers have proven successful for trapping of a single or a few particles. However, the method is slow and cannot be used for the smallest particles. Thus, it is not adapted to analyze a large number of nanoparticles, which is necessary to get statistically valid data. Here, we propose quasi-bound states in the continuum (quasi-BICs) in a silicon nitride (Si3N4) metasurface to trap smaller particles and many simultaneously. The quasi-BIC metasurface contains multiple zones with high field-enhancement ('hotspots') at a wavelength of 785 nm, where a single nanoparticle can be trapped at each hotspot. We numerically investigate the optical trapping of a type of biological nanoparticles, namely extracellular vesicles (EVs), and study how their presence influences the resonance behavior of the quasi-BIC. It is found that perturbation theory and a semi-analytical expression give good estimates for the resonance wavelength and minimum of the potential well, as a function of the particle radius. This wavelength is slightly shifted relative to the resonance of the metasurface without trapped particles. The simulations show that the Q-factor can be increased by using a thin metasurface. The thickness of the layer and the asymmetry of the unit cell can thus be used to get a high Q-factor. Our findings show the tight fabrication tolerances necessary to make the metasurface. If these can be overcome, the proposed metasurface can be used for a lab-on-a-chip for mass-analysis of biological nanoparticles.

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 (Lmax), TL vs. gonadosomatic index (GSI), TL-standard length (SL) regression and logistic model, the size at sexual maturity (Lm) 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 (KF) was suggested as the best condition factor (p < 0.0001), and relative weight (WR) 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 biology of Heteropneustes fossilis in a wetland ecosystem (Gajner Beel, Bangladesh) in relation to eco-climatic factors: Suggesting a sustainable policy for aquaculture, management and conservation.

The stinging catfish, Heteropneustes fossilis (Bloch, 1974) is a commercially important fish species in Asia. This is an important food fish as is enriched with high amounts of protein, iron and calcium. The current research demonstrates the population structure, size at sexual maturity, spawning- and peak-spawning season and fecundity of H. fossilis in an important wetland ecosystem - Gajner Beel in northwestern Bangladesh with an aim of its sustainable conservation through induced breeding and aquaculture practices. A total of 426 stinging catfish captured from the Gajner Beel through monthly sampling from January to December 2019 used in the study. Total length (TL), standard length (SL) and body weight (BW) of individual fishes were measured. The size ranges were with 6.70-24.10 cm TL, 1.37-83.94 g BW. Gonads were removed carefully through ventral dissection and weighted. Lm was 14.02, 13.5, 13.0 and 15.0 cm based on maximum length (Lmax ), TL vs. GSI (%), TL vs. SL and logistic model, respectively. Monthly variations of GSI and maturation stages were confirmed in April to August as spawning season and June as peak spawning month. Fulton's condition factor (KF ) was found to be with significant relations with GSI values. Fecundity was 1,730 to 23,870 and significantly correlated with both TL and BW. Temperature has been increasing 0.029 °C/year with the falling of rainfall at 2.96 mm/year in the study area. Environmental factors -Temperature, rainfall, dissolved oxygen and pH were found to be significantly correlated with GSI. We found the optimal range of temperature (29-31 °C), rainfall (350-380 mm), dissolved oxygen (5.0-6.0 mg/l) and pH (7.1-7.5) for spawning of H. fossilis. The paper recommended the policy guidelines to pave the ways of the aquaculture, conservation and management of H. fossilis in the changing eco-climatic events through specific management measures.

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 (a3.0), sexual maturity (Lm), spawning season, fecundity, mortality (i.e., total mortality (Z), natural-mortality (MW), and fishing mortality (F)), optimum catchable length (Lopt), length at first capture (Lc), 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. Lm was 9.60, 9.70, and 8.80 cm based on the gonadosomatic index (GSI), logistic, and maximum length (Lmax), 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, Mw was 0.97 year-1, and F was 0.83 year-1. Lopt was 11.14 cm (TL) and Lc 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.

Assessing reproductive biology of Macrobrachium lamarrei in the Ganges River (NW Bangladesh) in relation to environmental parameters.

Macrobrachium lamarrei (H. Milne-Edwards, 1837) is a well-known freshwater prawn species of Bangladesh. The aim of the research is to explore various reproductive aspects (size at sexual maturity, reproductive period and fecundity) of M. lamarrei in the Ganges River, Bangladesh through October 2012 to September 2013. We also study the environmental parameters and their impact on reproduction of M. lamarrei. A total 391 (ovigerous = 141, non-ovigerous = 250) female specimens were collected using Drag net. The TL50 (the TL at which 50% of individuals become mature) was calculated by a logistic equation as 5.20 cm. Based on the availability of ovigerous females the spawning season was February-November with the peak June-July. Further, 50% and 90% ovigerous females were observed when Fulton's condition factor (KF ) was 0.85 and 1.03, respectively. The total fecundity (FT ) was ranged from 65 to 370 where TL was 4.20-6.40 cm and BW was 0.84-2.50 g. Fecundity was found to be highly correlated with TL (r2  ≥ 0.96, rs  = 0.96, p < 0.0001) and BW (r2  ≥ 0.88, rs  = 0.93, p < 0.0001). Temperature (rp  = 0.82, p = 0.009), dissolved oxygen (DO) (rp  = -0.83, p = 0.0007), pH (rp  = 0.80, p = 0.0014) and total alkalinity (rp  = -0.87, p = 0.0002), were highly correlated with ovigerous females. The average temperature on peak spawning season was 32 °C. Also, the spawning period connected with the peak rainfall and showed a notable relation between rainfall and ovigerous females. In addition, exploration of long data series pointed that yearly average air temperature is rising by 0.029 °C yr-1, whereas yearly average rainfall is falling by 2.96 mm yr-1. Therefore, the result will be helpful for the sustainable management and conservation of M. lamarrei through fixed permissible mesh size and establishment of a ban period in the Ganges River, Bangladesh and adjoining ecosystems.

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 (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).

Dielectric optical nanoantennas.

Nanophotonics allows the manipulation of light on the subwavelength scale. Optical nanoantennas are nanoscale elements that enable increased resolution in bioimaging, novel photon sources, solar cells with higher absorption, and the detection of fluorescence from a single molecule. While plasmonic nanoantennas have been extensively explored in the literature, dielectric nanoantennas have several advantages over their plasmonic counterparts, including low dissipative losses and near-field enhancement of both electric and magnetic fields. Nanoantennas increase the optical density of states, which increase the rate of spontaneous emission due to the Purcell effect. The increase is quantified by the Purcell factor, which depends on the mode volume and the quality factor. It is one of the main performance parameters for nanoantennas. One particularly interesting feature of dielectric nanoantennas is the possibility of integrating them into optical resonators with a high quality-factor, further improving the performance of the nanoantennas and giving very high Purcell factors. This review introduces the properties and parameters of dielectric optical nanoantennas, and gives a classification of the nanoantennas based on the number and shape of the nanoantenna elements. An overview of recent progress in the field is provided, and a simulation is included as an example. The simulated nanoantenna, a dimer consisting of two silicon nanospheres separated by a gap, is shown to have a very small mode volume, but a low quality-factor. Some recent works on photonic crystal resonators are reviewed, including one that includes a nanoantenna in the bowtie unit-cell. This results in an enormous increase in the calculated Purcell factor, from 200 for the example dimer, to 8 × 106 for the photonic crystal resonator. Some applications of dielectric nanoantennas are described. With current progress in the field, it is expected that the number of applications will grow and that nanoantennas will be incorporated into new commercial products. A list of relevant materials with high refractive indexes and low losses is presented and discussed. Finally, prospects and major challenges for dielectric nanoantennas are addressed.

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.

Flexible Antennas: A Review.

The field of flexible antennas is witnessing an exponential growth due to the demand for wearable devices, Internet of Things (IoT) framework, point of care devices, personalized medicine platform, 5G technology, wireless sensor networks, and communication devices with a smaller form factor to name a few. The choice of non-rigid antennas is application specific and depends on the type of substrate, materials used, processing techniques, antenna performance, and the surrounding environment. There are numerous design innovations, new materials and material properties, intriguing fabrication methods, and niche applications. This review article focuses on the need for flexible antennas, materials, and processes used for fabricating the antennas, various material properties influencing antenna performance, and specific biomedical applications accompanied by the design considerations. After a comprehensive treatment of the above-mentioned topics, the article will focus on inherent challenges and future prospects of flexible antennas. Finally, an insight into the application of flexible antenna on future wireless solutions is discussed.

Tellurite glass defect-core spiral photonic crystal fiber with low loss and large negative flattened dispersion over S + C + L + U wavelength bands.

A defected-core spiral photonic crystal fiber is proposed to achieve very large negative flattened dispersion and small confinement loss. Simulation results reveal that the designed structure exhibits very large flattened dispersion over S+C+L+U wavelength bands and an average dispersion of about -720.7 ps nm(-1) km(-1) with an absolute dispersion variation of 12.7 ps nm(-1) km(-1) over the wavelength ranging from 1.45 to 1.65 µm. The proposed fiber has five air-hole rings in the cladding leading to very small confinement loss of 0.00111 dB/km at the excitation wavelength of 1.55 µm. The tolerance of the fiber dispersion of ±2% changing in the structural parameters is investigated for practical conditions.