Coastal communities in Bangladesh face significant challenges due to long-term salinity intrusion, leading to economic vulnerability and environmental stress. The remarkable adaptability of mud crabs to saline environments has encouraged coastal farmers to transition from shrimp aquaculture to mud crab fattening as an adaptive strategy. However, the sustainability of this practice is challenged by the overexploitation of wild seed, elevated mortality rates, suboptimal stocking densities and lack of standardized hatchery-produced crablets. Therefore, the present study aimed to evaluate the growth performance and survival of juvenile mud crabs (Scylla olivacea) reared at three different stocking densities (2, 4 and 6 crab/m2) randomly allocated in triplicate earthen grow-out ponds over a 90-day culture period. Hatchery-reared juvenile mud crabs (1.78 ± 0.18 g) were stocked into 80 m2 earthen ponds, where Nypa palm (Nypa fruticans) leaves were used as shelters covering 30% of the pond area. Survival rate, growth performance and key physicochemical parameters were monitored throughout the culture period. Principal component analysis (PCA) was also done to explain other factors that may influence the growth performance of crabs during culture. Crabs were fed once daily in southwestern areas with experimentally formulated feed with 45% protein. The findings revealed that stocking density significantly affected (p < 0.05) the survival rate. Crablets stocked at 2 and 4 crab/m2 had a significantly (p < 0.05) higher final mean weight than crablets stocked at 6 crab/m2. Crabs reared at a moderate stocking density (4 crab/m2) demonstrated higher yields than other treatments. Stocking with 6 crab/m2 exhibited the higher number of deformed crabs. These results indicate that a stocking density of 4 crab/m2 is recommended for the grow-out of S. olivacea crablets in earthen ponds. Optimal stocking density will provide scientific basis to enhance production efficiency, reduce mortality and promote sustainable mud crab aquaculture in Bangladesh.
Microalgal biomass has emerged as a valuable resource in recirculating aquaculture systems (RAS), due to its natural capacity to recover nutrients. In addition, microalgae are potential source of fish-feed in the aquaculture industry. However, its application in RAS needs careful consideration, as microalgae can interact with geosmin, a common off-flavor compound found in RAS, which may taint fish quality and makes it unsaleable for the market. In this study, we investigate the potential interaction between geosmin and different microalgal strains, Nannochloropsis oculata and a consortium of Tetraselmis suecica and Phaeodactylum tricornutum, including both living and dead biomasses. Experimental studies with dead biomass revealed that N. oculata and the microalgal consortium can uptake geosmin with an efficiency of 53 ± 0.48% and 25 ± 1.63% over 24 h, respectively. Similarly, with living biomass, uptake efficiencies were 54 ± 0.68% and 42 ± 4.14%, respectively. Based on the higher uptake efficiency, N. oculata was selected for further investigation. Different non-linear isotherm models (Langmuir, Freundlich, and Henry's Law), kinetic models (pseudo-first order model, pseudo second-order model, and Elovich model), and desorption study were used to understand potential sorption mechanisms and assess risks associated with geosmin accumulation in microalgal biomass. Geosmin adsorption by dead N. oculata was best described by Henry's isotherm law and the pseudo-second order kinetic model, while adsorption on living biomass aligned best with Langmuir isotherm model and the pseudo-second order kinetic model. Geosmin is released higher from living biomass (79 ± 3.18%) than dead biomass (47 ± 1.74%) when desorbed in water, suggesting harvested microalgae may contain geosmin. While microalgal water treatment combined with biomass utilization for fish feed fits very well within the circular economy, more research is needed to ensure the safe use of microalgal biomass.
Fisheries management increasingly demands robust forecasting tools to address growing environmental variability, anthropogenic pressures and complex ecological dynamics. This review systematically examines innovative modelling and forecasting approaches in fisheries, focusing on their descriptions, applications, strengths and limitations and comparative performance based on quantitative and qualitative evaluation criteria. Drawing on major scientific databases with studies published between 2000 and 2023, the review covers a broad spectrum of models, including Population Dynamics Models, Ecosystem Models, Statistical and Time Series Models, Machine Learning Models, Bioeconomic Models, Simulation Models, Spatial and Habitat Models and other emerging approaches. Historically, fisheries forecasting evolved from basic observational methods to advanced computational and statistical techniques. Conventional models such as surplus production and age-structured models remain valuable for certain stable systems with limited data. However, ecosystem-based models (e.g., Ecopath with Ecosim, Atlantis) and machine learning techniques (e.g., neural networks, random forests, deep learning) offer enhanced adaptability and predictive accuracy, particularly under dynamic and uncertain conditions. Despite these advances, challenges persist, including data scarcity, difficulties in model validation and integration of socio-economic and climate-related variables. Hybrid models that combine ecological, economic and social factors, especially those incorporating real-time data and artificial intelligence, show promise for improving fisheries forecasting. Progress in this field will require interdisciplinary collaboration, enhanced data systems and stronger policy integration to ensure sustainable fisheries management. This review provides a structured framework to guide researchers and decision-makers in selecting and developing more adaptive, accurate and actionable forecasting tools in the face of global environmental change.
Saprolegniosis, typically induced by oomycete Saprolegnia parasitica, is one of the most difficult pathogens in fish and other aquatic animals in freshwater systems. It is especially harmful for the endangered species landlocked salmon (Salmo salar m. sebago). Currently, there are only few alternatives to prevent and treat saprolegniosis occurrences, which can lead to major fish deaths and financial losses at fish farms. In this study, surface-modified cellulose materials were used at an experimental flow-through fish farm rearing landlocked salmon, which often suffers from saprolegniosis occurrences. The results showed that the material's cationic surfaces were able to capture the spores of S. parasitica (experimental part I and part II). The cellulose material was chemically modified with a high density of cationic quaternary ammonium groups, which performed better than a material with a weak cationic charge by amino groups obtained via physisorption of chitosan on the surface, resulting in fewer S. parasitica spores in the rearing tank water (experimental part I). The results are promising and offer a novel method for controlling saprolegniosis occurrences without harmful chemicals. However, certain environmental conditions (in experimental part II) inhibited the detection method (real-time quantitative polymerase chain reaction) used for the detection of S. parasitica. This highlights the need for further method development for the detection of S. parasitica. Overall, the results are promising in terms of reducing S. parasitica spores in rearing water and further controlling saprolegniosis occurrences. More process optimization is required to achieve the method's full potential in industrial scale processes.
The current study assessed the impact of organic and inorganic feeding management on water quality, growth performance and plankton communities in a pond-based polyculture system over 9 months, using three treatments: Ctrl (C), organic feeding (T1) and inorganic feeding (T2). Significant differences were observed in electrical conductivity (EC) and total dissolved solids (TDS), with inorganic feeding showing the highest EC (1719.95 ± 41.05 µS/cm, p = 0.0017) and TDS (884.80 ± 4.90 mg/L, p = 0.0122), while other water parameters such as DO, pH and temperature showed no significant variation (p > 0.05). In terms of growth, grass carp in organic feeding showed the highest weight gain (1264.0 ± 5.0 g) and specific growth rate (2.31 ± 0.01%/day), significantly higher than inorganic feeding (1089.4 ± 1.6 g, p < 0.0001). The overall gross yield was also highest in organic feeding (238,506.5 ± 29,668.4 g/ha, p < 0.0001). Phytoplankton and zooplankton diversity and abundance were significantly greater in organic feeding, with total densities of 31,224.0 ± 145.0 and 16,485.0 ± 524.0 cells/mL, respectively (p < 0.001). Proximate composition revealed significant improvements in organic feeding fish for protein (e.g., grass carp: 22.19 ± 0.79%, p < 0.0001), fat, ash and moisture content. Organoleptic evaluation also favored organic feeding, showing significantly better texture (8.16 ± 0.22), flavour (8.43 ± 0.26) and overall acceptability (8.01 ± 0.20) compared to organic and inorganic feeding management (p < 0.0001). These findings suggest that organic feeding management (organic feeding) improves water quality (excluding EC and TDS), enhances fish growth, promotes richer plankton communities and improves fish nutrition.
In the past half-century, fishing in one regional part of the Baltic Sea, the Stockholm Archipelago, has almost disappeared due to falling fish abundance, especially of herring (Clupea harengus). By examining published observations and archived material on historical fishing patterns, we found evidence of a remarkably continuous high level of fish supply throughout most of the nineteenth and twentieth centuries, despite variation in fish recruitment, high abundance of mammal predators and high fishing intensities. We observe that fishing was part of a true market, i.e., fishing acted as an opportunistic predator, abandoning specific target species at low abundance and fishing on present surpluses. Our study contributes to advancing historical marine ecology and adds to critiques of explanations of declining and collapsing fisheries in terms of inevitable ‘tragedies of the commons’. Our observations of historical management approaches contrast with contemporary Swedish fisheries management and may inform a different strategy towards achieving sustainable fisheries in the Baltic Sea and elsewhere.
Astaxanthin is a potent dietary carotenoid known to enhance growth and pigmentation in fish. This study evaluated the effects of graded dietary astaxanthin supplementation, extracted from Haematococcus pluvialis (0, 25, 50, 75 and 100 mg/kg) on growth performance, feed utilisation, body colouration and survival of Nile tilapia (Oreochromis niloticus). A total of 375 fish with initial weight (4.31 ± 0.37 g) were randomly distributed into fifteen 110 L tanks in triplicate groups and reared for 60 days. Feed intake and condition factor were not significantly affected among treatments (p > 0.05). Fish fed the 75 mg/kg diet exhibited significantly higher length gain (5.15 ± 1.04 cm), weight gain (14.90 ± 0.34 g) and specific growth rate (2.51 ± 0.14%/day) compared with other groups (p < 0.05). Feed utilisation was also improved, with the lowest feed conversion ratio (1.48 ± 0.04) and highest feed conversion efficiency (0.68 ± 0.02). Survival rate was highest at 75 mg/kg (97.44 ± 1.22%) with no significant difference (p > 0.05) from 100 mg/kg. Muscle carotenoid (4.84 ± 0.14 µg/g) and astaxanthin (0.22 ± 0.01 µg/g) increased dose dependently, with the greatest pigmentation observed at 100 mg/kg. Although the highest dose improved colouration, growth was slightly reduced compared with the 75 mg/kg group. These results indicate that 75 mg/kg dietary astaxanthin optimally enhances growth, feed efficiency, pigmentation and survival in Nile tilapia, supporting its use as a functional feed additive in aquaculture.
Trial Registration: Not applicable
The West African mangrove oyster, Crassostrea tulipa, exhibits high variability in shell morphology, which is influenced by both genetic and environmental factors. The current study investigated the plasticity of C. tulipa sub-populations within the Densu Estuary, Ghana, from May 2017 to October 2018 with respect to shell morphology, as impacted by some environmental parameters. The study is aimed at providing useful information on the plasticity of oysters in the face of harsh environmental conditions with respect to shell development. The study was carried out in Stations 1, 2, 3 and 4 (a and b), where oysters were present in Stations 3, 4a and 4b. Allometric studies were carried out on oyster samples from three sub-populations within the Densu Estuary. Temperature, DO, salinity, pH and turbidity were monitored. Bulk density of sediments at the sub-populations was determined. There was no marked difference in the variations of the physico-chemical parameters between Station 3 and Station 4 oysters, except for sediment bulk density. There was evidence of high mortality and low population density of oysters at Station 3, as compared to its counterparts. The slopes of the regression of shell height against shell length/total shell weight/wet meat weight of oysters from the various sampling stations showed negative allometry. Oysters at Station 3 showed isometric growth from the regression of shell width on shell height. Station 3 oysters demonstrated higher condition indices and gonadal indices indicative of better physiological status. The findings indicated that Station 3 oysters exhibited morphometric traits consistent with enhanced reproductive potential by demonstrating phenotypic plasticity through the development of bigger inner shell volume for gonadal development and maturation at small shell size in the face of harsh environmental conditions.
This study investigates the adaptation strategy of wild Asian seabass (Lates calcarifer) to artificial feed in an open floating cage over a period of 360 days. A total of 1800 wild seabass with an initial length of 19.91 ± 0.26 cm and a weight of 72.85 ± 3.94 g was stocked at a density of 15 fish per m3 in 60 m3 cages and subjected to two feeding strategies. In Treatment 1 (T1), fish were fed chopped tilapia (Oreochromis niloticus) across four feeding stages (S1, S2, S3 and S4). In Treatment 2 (T2), fish were fed chopped tilapia as their primary feed in S1, subsequently, chopped tilapia and commercial feed (45% protein) at a 1:1 ratio in S2, followed by commercial feed in S3 and finally formulated feed (37% protein) in S4 at 5%–1.2% of their body weight for 90 days in each stage. The growth performance included survival rate of 94.33%, weight gain (WG) of 1035.85 ± 34.09 g, specific growth rate (SGR) of 0.76 ± 0.01% per day, feed conversion ratio (FCR) of 2.75 and feed efficiency ratio (FER) of 0.36 in T1. In comparison, T2 exhibited a survival rate of 92.44%, WG of 1221.54 ± 47.79 g, SGR of 0.81 ± 0.02%/day, FCR of 2.45 and FER of 0.41. Proximate composition differed significantly among feeding stages, with a higher protein percentage observed in T2. Gut contents analysis revealed that fish predated natural food inside the cages, while intestinal morphology showed significant stage-dependent changes. Total production of seabass was 904 kg (15.07 kg/m3) in T1 and 1050 kg (17.5 kg/m3) in T2. The benefit-cost ratio (BCR) was 1.7 for both T1 and T2. Therefore, a gradual transition to formulated diets enhances growth performance and production efficiency of wild Asian seabass while maintaining economic viability in open cage aquaculture.
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