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Flyingfishes of the family Exocoetidae are sometimes difficult to identify solely based on morphology as members of certain genera share overlapping characteristics. Combining morphological and molecular analyses, the present study reports two specimens of stained flyingfish Cheilopogon spilonotopterus (Bleeker 1865) from the northern Bay of Bengal. As for COI gene sequences, nucleotide variations at five different positions (576 nucleotides identical out of 581 bp) were noted between two specimens of C. spilonotopterus and K2P genetic distances for all conspecific sequences ranged 0.000–0.050. The results of DNA barcoding, therefore, support the validity of both specimens as C. spilonotopterus at genetic level. These are the first DNA barcode records of C. spilonotopterus from the northern Bay of Bengal region.

Knowledge of bio-physicochemical variables is essential to better understand the functioning of tropical marine ecosystems, which are rich in biodiversity and provide nutrition and livelihoods to billions of people in the developing countries. This study analysed the spatial and temporal variability of phytoplankton and zooplankton with chlorophyll, primary productivity, temperature, salinity, oxygen and nutrients in the Bay of Bengal (BoB), collecting data from the World Ocean, and COPEPOD and Aqua MODIS records. The results indicated a strong gradient in bio-physicochemical conditions of the BoB, from the coast to the open sea. Specifically, the spatial variability in chlorophyll was negatively correlated (R2= 0.59) with temperature and zooplankton, while a positive correlation (R2= 0.70) was noted between chlorophyll and silicate, nitrate, phosphate, dissolved oxygen and salinity. All the variables exhibited a strong vertical gradient at depths up to 500 m. Temperature, nutrients, zooplankton and to a lesser extent salinity and rainfall had an influence on the annual abundance of phytoplankton. Over the long term, a significant positive trend in temperature and a significant negative trend in primary productivity were observed in the BoB. The findings of this study will be useful to draw insights on the state of fisheries habitats and the overall environmental conditions of the BoB in response to future climate changes.

Information on stock condition and reproductive biology are important for fisheries conservation and management planning. This study examined reproduction, growth, mortality and yield of sulphur goatfish (Upeneus sulphureus Cuvier 1829), which is a low-value food fish abundantly caught as bycatch in artisanal and industrial fishing from the southeast coast of Bangladesh at northern Bay of Bengal. Data were collected monthly obtaining samples from local fish landing center. The gonadosomatic index indicated that U. sulphureus spawns twice a year during January–May and August–October. Fecundity of the fish was positively correlated with the body and gonad weight, and varied from 15 128–97 274 eggs with fish weight 11.30–58.73 g. Monthly length–frequency distribution was analyzed through FISAT software, thus the estimated seasonalized von Bertalanffy growth parameters were L∞ = 21.80 cm, K = 0.54 per year, C = 0.5, WP = 0.1 and Rn = 0.300, respectively. Moreover, the value of seasonalized total mortality coefficient Z (2.24) was smaller than that of the non-seasonalized Z (4.16). The instantaneous natural mortality and fishing mortality, calculated for non-seasonalized total mortality, were 1.31 and 2.86, respectively. Furthermore, the high exploitation rate (E = 0.69) was close to maximum exploitation level (Emax = 0.75) in yield-per-recruit analysis, suggesting that U. sulphureus is being exploited at the MSY (maximum sustainable yield) level. Therefore, further increase in fishing effort may reduce U. sulphureus stocks in the coastal waters of Bangladesh.

Tropical hilsa shad (Tenualosa ilisha) contributes significantly to the society and economy of Bangladesh, India and Myanmar, but little is known about their habitats across the life cycle and their relationship with environmental drivers. This study describes spatial and temporal variability of productivity in the Bay of Bengal (BoB) relating to hilsa fishery. Decadal data on net primary productivity, nutrients (i.e. nitrate, phosphate and silicate) and zooplankton were collected from Aqua MODIS, world ocean database and COPEPOD respectively with spatial resolution 1°×1°. Moreover, monthly abundance of phytoplankton, hilsa catch and long-term catch dynamics were analyzed to determine the associations between variables. The present study was extended over 3.568 million km2 area, of which 0.131–0.213 million km2 area characterized as the most productive with net primary production of >2,000 mg C/m2/day, 0.373–0.861 million km2 area as moderately productive with 500–2,000 mg C/m2/day, and 2.517–3.040 million km2 area as the least productive with 2/day which were consistent with field verification data. In case of nutrients, the Ganges-Brahmaputra-Meghna (GBM) delta was rich in nitrate and phosphate than that of the Ayeyarwady delta, while silicate concentration persisted high all over the northern BoB including the deltas. A peak abundance of phytoplankton was observed in GBM delta during the months of August-November, when ~80% of total hilsa are harvested in Bangladesh annually. Variations in seasonal productivity linked with nutrients and phytoplankton abundance are important factors for predicting hilsa habitat and their migration patterns in the deltaic regions and shelf waters of BoB. These results can be useful in forecasting potential responses of the hilsa in BoB ecosystem to changing global ocean productivity.

Temporal changes in biological characteristics of small yellow croaker Larimichthys polyactis in the Yellow Sea were examined for the period of 1960–2008. The body size and age of small yellow croaker decreased substantially, in particular, average length of fish in 2008 was reduced by ~85% than those occurring in 1985, and at that time ~93% of the total catch was dominated by one-year-old individuals. Correspondingly, growth parameters also varied significantly over the years, i.e., k (growth coefficient) and t 0 (zero-length age) gradually increased from 0.26 and–0.58 year in 1960 to 0.56 and–0.25 year in 2008, respectively. Although, L∞ (body length) sharply decreased from 34.21 cm in 1960 to 24.06 cm in 2008, and t r (inflexion age) decreased from 3.78 year in 1960 to 1.61 year in 2008. There was a great increase both in natural mortality coefficient and fishing mortality coefficient. However, according to the gray correlation analysis, changes in the biological characteristics of small yellow croaker were induced by different stressors ranked as: fishing vessel power>feeding grade>sea surface temperature. This study suggests that the active fishery management measures for biological characters of fish populations should be considered.

Aquatic habitat connectivity is vital for the continued existence of migratory fish. Using GIS and outranking multicriteria analysis based on hydrometeorological data, this study describes habitat preference of egg, fry, juvenile and adult phases of hilsa shad, Tenualosa ilisha (Hamilton), as well as their spawning areas in the aquatic ecosystems of Bangladesh. The total area studied was 29 484 km2, about 29% of which belonged to the Meghna, Shahbajpur, Tetulia and Ander Manik rivers, and the channels of Sandwip, Kutubdia and Moheshkhali islands, which provide the most suitable habitat for the species. An additional 27% of moderately suitable area was located in other deltaic rivers and inshore waters. The remaining 44% was offshore deeper water, which was least suitable for hilsa. The most suitable area for spawning, eggs, fry, adults and juveniles was 6, 11, 29, 38 and 56% of the area, respectively. The model outputs were validated against field measurements and fishers’ indigenous knowledge with an accuracy level of 92%. Thus, this study provides key information about the location of hilsa at different stages of its life cycle, information useful in understanding its occurrence over a relatively large geographical area. Information of this kind is useful in fishery conservation and management.

A sanctuary is a specific form of protected area and considered to be an important management measure for the conservation and management of fisheries resources. Using socioeconomic and biological indicators, this study investigates the perceptions of fishers towards sanctuaries that were established in the rivers of Meghna and Padma and in inshore waters of Bangladesh since 2005 to protect the declining hilsa ( Tenualosa ilisha ) populations. Both qualitative and quantitative data were collected from six communities adjacent to five hilsa sanctuaries and then analyzed to know the socioeconomic profile of fishers as well as their perceptions of the performance of sanctuaries. The majority of fishers felt that an apparent recent increase in hilsa catch is due to the establishment of sanctuaries. Their perception is well supported by catch statistics that show higher overall hilsa production both from inland and marine waters. However, fishery closure led to substantial economic hardship due to lost income. If the sanctuaries are to function effectively, issues (e.g. lost income) affecting fishers must be addressed by offering compensation schemes so that fishers are able to support their families. The process has to be transparent, inclusive and equitable. There is also a need to support alternative livelihoods for fishers in order to reduce dependence on hilsa fishing. Moreover, fishers must be provided with economic and/or other incentives so as to share responsibilities to protect and manage sanctuaries successfully. Since fishers’ involvement is key to the success of sanctuaries, social acceptance of fish sanctuaries by fishers is a must.

Global warming is a major threat to the natural environment worldwide with potential adverse impact on plankton community. This will ultimately lead to a change in the dynamics of aquatic food webs. In this study we used seasonally forced multi-species version of the classic Rosenzweig–MacArthur predator–prey model to understand the role and stochastic influence of increasing temperature on marine plankton. First, stable coexistence of four phytoplankton and three zooplankton species was created in a system and then the level of temperature changed to achieve our research goal. We found that the stable coexistence of phytoplankton and zooplankton was related to periodic shifts in species biomass, variation in inter-specific competition and niche configuration. Warming significantly reduced total plankton biomass and changed turnover time of a species, with gradual warming breaking the stable coexistence of phytoplankton and zooplankton. In addition, we found that warming make specialist species more vulnerable than generalist species. After adding noise, a significant variation was observed in plankton biomass and amplification of noise was higher for phytoplankton compared to zooplankton. These results suggest that stochastic or unpredictable nature of temperature fluctuations may create a window of opportunity for the emergence of new species. Overall, warming would induce a shift in plankton dynamics and thereby exert pressure on plankton dependent communities such as fish in the long run.

Highlights: • Nutrients and zooplankton were the most important predictors for diatom. • Temperature and zooplankton had a negative effect on diatom. • Species interaction explained 20% variability in diatom abundance. • Six environmental variables explained 57% of the variability. Abstract: Temporal variability in phytoplankton is driven by a range of biotic and abiotic factors. In this study, we aimed to identify and estimate the important explanatory variables affecting the diatom species and their abundance in the coastal waters of Bangladesh. For this, species interaction and six explanatory variables were taken into consideration to develop a density dependent Bayesian regression model for quantifying the relative importance of different explanatory variables causing the variability in diatom abundance. Thus, three nutrients such as silicate, nitrate and phosphate, and zooplankton were identified as the most important predictors for 19–25 species. Moreover, the effect of three nutrients and salinity was positive for most diatoms, while temperature and zooplankton had a negative effect. Species interaction and environmental variables combinedly explained 77% of the variability in diatom abundance, with the latter being the dominant factor. Specifically, six environmental variables combinedly explained 57% of the variability in diatom abundance and the remaining 20% of the variability was due to species interaction. This is the first modelling study on phytoplankton community describing the dynamics of diatom species in the coastal waters of northern Bay of Bengal.

The availability of suitable freshwater spawning habitat is considered to be a major factor limiting the natural recruitment of anadromous Hilsa shad (Tenualosa ilisha) in the coastal waters of Bangladesh. Against this context, we applied georeferenced habitat database to determine spawning habitat suitability index of Hilsa shad. Landsat imagery and thematic layers were analyzed with ENVI and GIS, and developed a series of GIS models to identify and ranking of suitable spawning grounds. Thus, among the studied 29,484 km2 aquatic ecosystems, only 6% (=1851 km2) area is the most suitable consisting of the rivers Meghna, Shahbazpur, Tetulia and Ander Manik as well as the channel of Sandwip island. Whereas, 20% (=5996 km2) area including river, estuary and near shore water bodies are moderately suitable, and in particular, the offshore deep waters occupying 73% (=21,637 km2) area is least suitable. The model outputs were verified after field data of fishers’ indigenous knowledge with an accuracy level of 87%. This study suggests that necessary measures, such as conservation and management of spawning habitat should be implemented for an increased reproductive and recruitment success that will eventually improve populations of wild Hilsa shad in Bangladesh.

Hilsa shad Tenualosa ilisha comprises the largest and most valuable single fishery of Bangladesh. This study was conducted to identify suitable habitats for Hilsa juvenile in the northern Bay of Bengal along the coast of Bangladesh using Geographical Information Systems (GIS) based Multi-Criteria Evaluation (MCE) of water temperature, dissolved oxygen, pH, salinity, turbidity, current, depth and rainfall. Landsat imagery and 8 thematic layers were analyzed with ENVI and GIS capabilities, and developed as a series of GIS models to identify and prioritize the appropriate habitats for Hilsa juvenile. The study covered 29.484 km2 water body and revealed that 56% (16.388 km2) is the most suitable, 21% (6.054 km2) is moderately suitable and 24% (7.042 km2) is not suitable which was consistent with field verification. The assemblage of marinebrackish-freshwater ecosystems with favourable ecological parameters and rainfall patterns are very much important for supporting juvenile Hilsa in the study area. The results are useful for habitat-specific sanctuary development as the efficient conservation may lead to higher production of adult Hilsa and increase the economic benefit to the fishers.

Subcellular components of the probiotics Aeromonas sobria GC2 and Bacillus subtilis JB-1, when administered to rainbow trout, Oncorhynchus mykiss, conferred protection against a new biogroup of Yersinia ruckeri. Thus, intraperitoneal or intramuscular injection of rainbow trout with cell wall proteins (CWPs), outer membrane proteins (OMPs), lipopolysaccharides (LPS), whole cell proteins (WCPs) and live cells followed by challenge on day 8 with Y. ruckeri led to 80-100% survival compared with 10% survival in the controls. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of WCPs and OMPs from GC2 had 10 and 5 variable protein bands in comparison to 11 and 5 bands in the WCPs and CWPs from JB-1. Proteomic analyses were employed following SDS-PAGE to categorize one dominant protein of 104.7 kDa from the CWPs of JB-1 and equated it with 'Bacillus spp. endoglucanase' with a Mascot score >69. These results point to the potential of using cellular components of probiotics for protection of fish against bacterial diseases.

Site selection is a key factor in any aquaculture operation, affecting both success and sustainability as well as solving land or water use conflicts. This study was conducted to identify suitable sites for carp farming development in urban water bodies (UWBs) of Chittagong, Bangladesh using Geographical Information Systems (GIS) based MultiCriteria Evaluation (MCE) of water, soil and infrastructure database. ASTER imagery and 14 thematic layers were analyzed with ENVI and GIS capabilities, and developed a series of GIS models to identify and prioritize the appropriate UWBs for carp farming. The study identified 487 UWBs occupying 362 ha and revealed 280 ha (77%) is the most suitable, 36 ha (10%) is moderately suitable and 46 ha (13%) is not suitable which was consistent with field verification. The results are encouraging for extension of carp culture and diversify the economic activities of the urban dwellers.

The species identification, distribution pattern, density and biomass of salt marsh and seagrass plants with some of the ecological parameters were studied in the Bakkhali river estuary, Cox's Bazar, Bangladesh during the first half of 2006. Two salt marsh species ( Spartina sp. and Imperata cylindrica ) and one seagrass species ( Halophila beccarii ) were identified during this investigation, providing the first reports of Spartina sp. and H. beccarii in coastal Bangladesh. Seagrass H. beccarii was found in an accreted area and co-existing with salt marsh, and scattered sparsely in the salt marsh habitat and macroalgae Ulva intestinalis . Flowering and fruiting were recorded from the seagrass H. beccarri during January and February. No flowers and fruits were observed for the salt marsh Spartina sp. during the study period. Results showed that the shoot density of Spartina ranged from 400 to 2875 shoots m −2 with the highest total biomass (165.80 g dry weight (DW) m −2 ) in March. Shoot density of H. beccarii ranged from 2716 to 14320 shoots m −2 in this estuarine coastal environment. The total biomass of seagrass was higher (17.56 g DW m −2 ) in March compared to the other months. The highest H. beccarii above ground (AG) biomass and below ground (BG) biomass were 9.59 g DW m −2 and 9.42 g DW m −2 , respectively. These parameters are comparable with those generally observed for the salt marsh and seagrass species in the other places of the world.

Probiotic Kocuria SM1, which was part of the allochthonous gut microbiota of rainbow trout, was administered to rainbow trout (Oncorhynchus mykiss) fingerlings as dietary supplement at approximately 10(8) cells g(-1) for two weeks. The fish were challenged with Vibrio anguillarum and innate immunity determined over the following 5 weeks. The probiotic-fed fish survived (mortalities = 10-28%; P0.05) better than the controls (mortalities = 73-92%) for 5 weeks after stopping administration of Kocuria SM1, although the relative percent survival (RPS) declined steadily from 87 to 36% by the end of the experiment. A significant (P0.05) effect on the immune parameters was observed in fish within 3 weeks after stopping administration of Kocuria SM1 in comparison with the controls, i.e. enhancement of the respiratory burst (OD(550nm)) from 0.051 +/- 0.014 to 0.067 +/- 0.009, lysozyme 605 +/- 185 units ml(-1) to 872 +/- 114 units ml(-1), total protein 19.8 +/- 2.0 mg ml(-1) to 23.8 +/- 0.8 mg ml(-1) at 2 weeks, and leukocrit 2.9 +/- 1.8% to 5.1 +/- 1.1%, peroxidase (OD(550nm)) 0.23 +/- 0.02 to 0.37 +/- 0.11 and bacterial killing activities (percentage of surviving bacteria = 82 +/- 12% to 57 +/- 4%) at 3 weeks. Generally, the levels reduced progressively towards the end of experiment.