Hydrobiology

This research investigates the effects of incorporating cyanobacterium Oscillatoria limnetica (OL) powder into aquafeeds on the growth rates, activity of digestive enzymes, antioxidant status, and innate immune responses of white-leg shrimp, Litopenaeus vannamei. The shrimps’ resistance against possible infection with Vibrio harveyi was also examined. For 12 weeks, shrimps (1.26 ± 0.088 g) were nourished on experimental diets with 0.0, 0.75, 1.5, 2.25, and 3.0 g OL/kg feed, represented as OL0, OL0.75, OL1.5, OL2.25, and OL3.0, respectively. At the end of the feeding trial, shrimps were challenged by V. harveyi, and their mortality was further observed for further ten days. The shrimps fed on OL-enriched diets, particularly OL3.0, showed significantly greater growth, digestive enzyme activities, and innate immunity performance than those fed on the control diet (OL0). Compared to the control group, enzymatic antioxidant parameters (CAT and SOD) were significantly (p < 0.05) higher; meanwhile, MDA levels showed marked declines in shrimps fed on OL-containing diets (particularly OL3.0). The relative mRNA expression of antioxidant-related genes (cMn-SOD, CAT, and GPx) and immune-related genes (HMC, Alpha2M, ProPO, and Pen3a) was upregulated in the OL-fed animals compared to the control group. The intestinal morphometry was markedly enhanced in the animals fed on OL-enriched diets, especially with respect to the OL3.0 diet. After the bacterial challenge assay against V. harveyi for ten days, shrimps fed on the control diet had 83.3% mortality; meanwhile, the mortality rate was lower in shrimp groups fed on OL diets, particularly OL3.0 (46.7%). This study demonstrates that L. vannamei benefits from dietary inclusion of O. limnetica (3.0 g/kg feed) through accelerating its growth due to better digestion of diets. Additionally, the OL meal acts as a functional ingredient that fortifies the shrimp against possible V. harveyi infection by enhancing their biological defense system. Full article

Freshwater ecosystems are increasingly affected by anthropogenic stressors, necessitating the assessment of sensitive biomarkers of sublethal impact. This study assessed the seasonal variability of oxidative stress parameters in the amphipod Gammarus lacustris from three tributaries of Lake Sevan (Armenia)—the Gavaraget, Karchagbyur, and Argichi Rivers—with contrasting hydrophysical and hydrochemical conditions. During 2022–2024, lipid peroxidation (MDA), antioxidant enzymes (CAT, SOD, GR, and GST), and glutathione (GSH) were measured in specimens collected in May, July, and October and related to temperature, dissolved oxygen, nutrients, major ions, and trace elements. Biomarker levels generally increased from spring to summer and declined in autumn, following temperature and photoperiod patterns. Statistically significant seasonal dynamics were most consistent in the Karchaghbyur River, while, in the Gavaraget and Argichi Rivers, they varied by biomarker and year. Amphipods from the Gavaraget River exhibited consistently elevated levels of oxidative stress biomarkers, consistent with elevated nutrient concentrations and stronger anthropogenic impacts. A short-term increase in all biomarkers in the Argichi River in 2023 indicated episodic acute stress. Overall, the response of oxidative stress biomarkers in G. lacustris reflected both the natural seasonal variability and spatial differences in environmental pressure, confirming their potential as a tool for monitoring Lake Sevan’s tributaries. Full article

Significant cyanobacterial proliferations dominated by Lyngbya have been increasingly reported since the 2000s, posing environmental, economic, and human-health risks. This review synthesizes their distribution, predictors, toxicity, and management strategies of all identified Lyngbya species, including species historically classified as Lyngbya despite later taxonomic changes. Research has focused mainly on Lyngbya majuscula and Lyngbya wollei. For L. majuscula, bloom initiation is driven by proximate abiotic factors such as nutrients, light, and temperature; while broader conditions, including bottom currents, sediment nutrients, rainfall, and land use, set the stage for proliferation. Toxin production appears related to nutrient levels and temperature, although mechanisms remain poorly understood. Management of L. wollei commonly relies on copper-based chelated algaecides, despite their risks to non-target organisms, highlighting the need for more sustainable tools used in managing other cyanobacteria. Existing predictive models for Lyngbya proliferation show limited accuracy, partly due to insufficient in situ data. This review argues that novel monitoring approaches could provide the data needed to strengthen predictive models, also offering insights into a new modeling approach, supporting more proactive and effective Lyngbya bloom management. It is particularly valuable for research in water resource management and environmental science, as it synthesizes current knowledge essential for advancing management strategies. Full article

Eastern Boundary Upwelling Systems (EBUSs) are among the most productive marine biomes globally, renowned for their substantial pelagic fisheries. While the role of wind-driven upwelling in stimulating primary production is well-documented, the integral contributions of the marine benthos in maintaining ecosystem productivity and fishery yields are often underrepresented. This article analyzes evidence from the Humboldt, California, Benguela, and Canary Current systems to delineate the critical functions of the seabed and its resident communities. Three primary pathways through which the benthos supports fisheries are described: (1) by facilitating the efficient regeneration of nutrients from sedimenting organic matter, thereby replenishing the inorganic nutrient pool for subsequent primary production; (2) by providing essential habitat structure that supports the life history of a myriad of species, including demersal and coastal fish species, serving as nursery and feeding grounds; and (3) by forming the foundational trophic base for benthic-feeding fishes and invertebrates of commercial importance. By comparing system-specific characteristics, such as the influence of oxygen minimum zones on benthic community structure, the integrity of the benthic subsystem as a fundamental determinant of the productivity and sustainability of EBUS fisheries is demonstrated. A holistic management approach that includes benthic habitat conservation is therefore paramount. Full article

The present study describes the reproductive cycle of the razor clam (Solen marginatus) from the Ria Formosa lagoon in the Algarve region (southern Portugal), using histological preparations of gonads from samples collected monthly over an 18-month period, from January 2023 to June 2024. Simultaneously, the mean gonadal index (GI) was estimated and its relationship with fluctuations in seawater temperature and chlorophyll a concentration was examined. The reproductive cycle of S. marginatus showed a seasonal pattern, with a resting period between August and October, followed by the onset of gametogenesis in November, which lasted until March. Ripe individuals were observed between February–March and May, with the spawning period occurring primarily between May and July. The mean GI reflected the temporal variation in the gonadal cycle. Reproduction in this species was strongly influenced by fluctuations in seawater temperature, but was not significantly correlated with chlorophyll a concentration. The information gathered in this study is of utmost importance, as it enables the proposal of evidence-based management measures aimed at promoting the sustainable exploitation of this resource. According to these new findings, a closed season (June or July) prohibiting razor clam harvesting in the Ria Formosa lagoon between May and July is proposed. Full article

The physiological performance of the Pacific oyster Magallana gigas in subtropical lagoon systems is shaped by the interaction between environmental variability, reproductive dynamics, and oxidative stress. This study quantified monthly changes in the growth and proximate composition of oysters cultivated in Estero La Cruz, Sonora, and evaluated their relationship with temperature and chlorophyll-a as proxies for thermal stress and trophic availability. Shell growth was continuous, while somatic biomass increased markedly during winter, indicating high thermal tolerance and metabolic flexibility. Proximate composition showed pronounced seasonal oscillations, with energy reserves accumulating during periods of high primary productivity and declining sharply in December, coinciding with peak gametogenic activity. Antioxidant enzyme activities (SOD, CAT, GPx) increased toward winter, reflecting elevated oxidative stress. Correlation and regression analyses revealed consistent relationships among environmental variables and biological responses, identifying temperature as the main factor associated with growth variability. Overall, these results demonstrate a strong coupling between environmental forcing, energy allocation, and oxidative stress, providing an integrative framework for understanding oyster performance and supporting aquaculture management in subtropical coastal systems. Full article

Fast, reliable detection methods are paramount in the fight against the spread of aquatic invasive species (AIS), and eDNA techniques provide many benefits over traditional sampling methods. AIS are spreading rapidly around the world, reshaping ecosystems, outcompeting native species, and experiencing explosive population growth. Some sources cite the Laurentian Great Lakes as the most heavily invaded freshwater system in the world. The advantages of using eDNA technology for AIS detection include: (1) it is often more sensitive, (2) it can cover much more area, (3) it is less destructive, (4) it does not require trapping of threatened species, and (5) it can be done with considerably less taxonomic training. This study was implemented to test the utility of a commercially available metabarcoding assay against a targeted, qPCR approach for the detection of four AIS in Lake Erie. We sampled eight localities monthly throughout the summer of 2024 using both techniques. Our target AIS were the bloody red shrimp Hemimysis anomala, the fishhook waterflea Cercopagis pengoi, the water flea Daphnia lumholtzi, and the gammarid scud Echinogammarus ishnus. We found that the targeted, qPCR approach was more successful at AIS detection for our four target organisms than the specific, commercially available metabarcoding assay that was used. Full article

Whale sharks (Rhincodon typus) predominantly inhabit the epipelagic layer, yet dives to at least 1928 m have been reported. Even so, current understanding of the species’ true maximum dive depth is constrained by the technological limitations of depth sensors of commercially available satellite tags, which are generally rated to a maximum depth of 2000 m. Here, we report a new maximum depth range of 1978–2527 m inferred from a Wildlife Computers custom-calibrated SPLASH10-346C finmount tag (2500 m capability), deployed on a 7 m juvenile male whale shark in the Coral Sea, Australia. This extends the currently accepted depth limit by 50–599 m. Full article

Given the low efficiency of current actions regarding the restoration of a critically endangered species, the Sevan trout, there is an urgent need for the evaluation of ongoing strategies and prioritization of the most efficient ones. Thus, the aim of this study was the scientific justification of the effectiveness of various restoration strategies for Sevan trout wild stocks. For this, we developed an experimental design to estimate the efficiency of stocking the main spawning rivers with fingerlings. Sevan trout subspecies were released and re-captured to measure their growth rates and biological features. Also, we conducted assessments of the abiotic conditions and ecological status of rivers. Because Sevan trout fingerlings have also been used to directly stock Lake Sevan by the Foundation for “Restoration of Sevan trout stocks and development of aquaculture” in recent years, we set gill nets to capture and study Sevan trout from the lake. The results showed that releasing summer trout less than 1 g in weight into the inlets of Lake Sevan is ineffective. Although larger gegharkuni had higher survival rates, the current state of the rivers will hardly ensure the sustainability of stocks. Current investigations have also shown the viability of stocking into the lake, as supported by both 2+- and 3+-year-old specimens being reported. However, further studies of the spatial dispersion and survival of stocked juvenile trout and the state of spawning grounds in the lake would help improve restoration strategies. Full article

Monoenoic fatty acids (MUFAs), defined by the presence of a single carbon–carbon double bond within a long aliphatic chain, constitute a structurally diverse and ecologically significant class of lipids widely distributed in aquatic organisms. In marine and freshwater environments, MUFAs are fundamental components of membrane phospholipids and storage lipids, where mono-unsaturation modulates melting point, lipid packing, and bilayer dynamics, enabling homeoviscous adaptation to fluctuations in temperature, pressure, salinity, and oxygen availability. Positional and geometric isomerism (e.g., cis-Δ5, Δ7, Δ9, Δ11, Δ13, and trans forms) further enhances biochemical diversity, providing sensitive chemotaxonomic markers and indicators of trophic transfer across food webs. In addition to common straight-chain monoenes, rare methyl-branched, cyclopropane-containing, and acetylenic derivatives occur in specialized aquatic taxa, reflecting evolutionary adaptation and ecological niche differentiation. Computational QSAR analyses suggest that monoenoic fatty acids and their unusual analogues occupy bioactivity spaces associated with lipid metabolism regulation, vascular and inflammatory modulation, antimicrobial defense, and membrane stabilization. This review integrates structural chemistry, biosynthesis, ecological distribution, trophic dynamics, and predicted biological activity of monoenoic fatty acids in aquatic systems, highlighting their dual role as adaptive membrane constituents and as biologically active mediators linking molecular lipid architecture to hydrobiological function and environmental change. Full article

This study presents the first comprehensive checklist of Porifera along the Libyan coast, integrating historical data from grey and published literature with new records obtained from recent field surveys. Despite the historical relevance of sponge fisheries in Libya, knowledge of sponge diversity in the region remains remarkably fragmented. To address this gap, underwater surveys were conducted at the Gara and Bsis Marine Protected Areas (MPAs), where sponge specimens were collected and identified through morphological analyses. Previous studies documented 44 sponge species in Libya, with Demospongiae as the dominant class. The recent field surveys at the Gara and Bsis Island MPAs documented a total of nine species, including two new records for Libyan waters, Chalinula renieroides and Ircinia variabilis, both identified from the Gara MPA. These new records expand the known distribution of Mediterranean demosponges and contribute to a better understanding of their biogeographic patterns in an understudied region. Overall, the updated checklist comprises 46 species and represents an essential baseline for the Libyan coast. This study underscores the importance of future monitoring, emphasizing the expansion of systematic surveys, the investigation of diverse habitats, and the integration of molecular approaches to ensure a comprehensive understanding and effective conservation of Libya’s marine sponge heritage. Full article

This study addresses a long-term failure to achieve the good ecological status for fish fauna required by the European Water Framework Directive (WFD) in the salmonid–rhithral zone in Bavaria, Germany. To identify the causes, we compared extensive fish population data from the Eger River with data from its twin river, the Röslau. The proportion of autochthonous cold, oligo-stenothermic fish species is significantly lower in the Eger (4.97% vs. 37.31%). In addition, continuous water temperature measurements were taken at five locations from spring to early autumn in 2023. The Eger showed significantly higher water temperatures throughout the measurement period. In midsummer, differences in daily maximum temperatures exceeded 10 °C at the same altitude. The proportion of cold-water fish in the population appeared to be negatively related to the mean of summer water temperature peaks (MWTP) (R = 0.95, p < 0.01). Accordingly, restoration measures in the Eger would need to reduce the MWTP from the current 19.1–20.5 °C to at least 16–16.5 °C, which requires more detailed data on the thermal footprint of individual hydraulic structures. The anthropogenic thermal impact on the Eger was overlooked as the root cause of the problem for many years, which largely explains the ineffectiveness of previous restoration measures. At least within the salmonid–rhithral zone, we consider the ability of the standardized fish-based assessment tool (fiBS) to detect thermal deterioration to be sufficient, provided it is applied with due care. Full article

In the past decade, non-native suckermouth armored catfish, Pterygoplichthys spp., have spread throughout the highland rivers of Lam Dong province, Vietnam. We examined spatial and temporal variation in endocrine and biochemical profiles across different river reaches, river systems, and between two sampling years (2020 and 2022). Seven blood parameters related to metabolism and energy balance were measured: total and free triiodothyronine, cholesterol, triglycerides, total protein, creatinine, and direct bilirubin. Concentrations of thyroid hormones and cholesterol did not differ significantly across sites or years. Multivariate analyses indicated that thyroid-related pathways were only weakly influenced by the environmental variation, suggesting preserved thyroid homeostasis. In contrast, triglycerides, total protein, creatinine, and direct bilirubin varied among rivers and between years at the same site, likely reflecting differences in food availability and energy balance. These results suggest that biochemical variation in non-native armored catfish is primarily expressed through lipid metabolism and protein turnover, while thyroid function remains comparatively conserved across invaded river habitats. Full article

The Water Framework Directive 2000/60/EC requires the assessment of the ecological quality in all surface waters using biological indices, yet the effective application of these indices often demands extensive and long-term monitoring data. Oxidative stress biomarkers offer a promising complementary approach, as they can detect early biochemical responses of organisms to environmental degradation. In this study, we evaluated the suitability of two oxidative stress biomarkers—malondialdehyde (MDA) levels and DNA damage—in the gonads of a freshwater fish species, the Prussian carp Carassius gibelio (Bloch, 1782) as indicators of ecological condition in lakes of differing environmental quality. Fish were sampled from four lakes (Doirani, Vegoritida, Volvi, Petron; Northern Greece) representing a gradient of physicochemical and ecological quality. Both MDA concentrations and DNA damage showed significant (p < 0.05) differences among lakes. However, only DNA damage in the gonads was significantly (p < 0.05) associated with lake ecological quality as determined by the Greek Lake Fish Index (GLFI), with higher biomarker responses observed in lakes of poorer status. These findings demonstrate that oxidative stress biomarkers in C. gibelio reflect variations in lake ecological quality and may serve as sensitive, early-warning tools for biomonitoring and pollution assessment in freshwater ecosystems. Full article

Small pelagic fish, including sardines, are essential to global fisheries and aquaculture feed production. However, these species are increasingly exposed to intense exploitation. In Chile, the common sardine (Strangomera bentincki), endemic to the Humboldt Current System, supports major industrial and artisanal fisheries. Landings are expected to reach 300,000 tons by 2025, mostly for fishmeal production. As a keystone species, S. bentincki is highly sensitive to environmental variability during early development, which can reduce recruitment and threaten long-term population sustainability. This interdisciplinary approach integrates ecological and biotechnological perspectives to assess the feasibility of controlled juvenile sardine production in land-based Ecological Aquaculture (EA) systems, including Recirculating Aquaculture Systems (RAS) and Integrated Multi-Trophic Aquaculture (IMTA), which are designed to reduce environmental impacts. These systems enable precise control of temperature, feeding regimes, and water quality, facilitating investigations into larval and juvenile survival, growth performance, and physiological responses under variable thermal and nutritional conditions. Emphasis is placed on fatty acid metabolism during ontogeny, particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are essential for somatic growth, reproductive development, and thermal tolerance. Developing standardized protocols for juvenile S. bentincki culture addresses key gaps in husbandry and physiology (temperature threshold, nutrient density, larval growth rate, etc.) while introducing a novel ecological–aquaculture integration framework. This approach links early-life ecology with applied rearing techniques to support stock enhancement, strengthen artisanal fisheries, and promote sustainable aquaculture diversification under increasing environmental variability. Full article

Understanding the behavioral strategies that allow freshwater mussels to persist under environmental stress is essential for their conservation, yet burrowing behavior remains poorly quantified. We tested whether valve movement data could be used to detect and characterize burrowing in the endangered Westralunio carteri; a species endemic to a region undergoing severe climatic drying. Mussels from multiple populations were monitored individually under laboratory conditions using Hall effect sensors, and valve movement patterns were analyzed to distinguish between burrowing and non-burrowing behaviors. Burrowing was associated with rapid, high-amplitude valve movements that lengthened as burial progressed, while non-burrowing behaviors showed distinct, slower patterns. These differences indicate that valvometry can reliably identify burrowing behavior, providing a non-invasive method for monitoring mussel activity. This approach has broad applications for ecological research, conservation assessment, and early-warning biomonitoring of imperiled freshwater mussel populations. Full article

The Austro-American Side-necked Turtles originated in Gondwana and are found only in South America and Australasia. This paper aimed to review the reproductive aspects of the Chelidae family systematically. The searches were conducted in several databases, resulting in 86 studies, of which only 21 were considered adequate. The research was mainly conducted in Australia and Brazil, in both natural and laboratory settings, across different ontogenetic stages among the sixteen species studied. The analyzed publications focused on different aspects of the reproductive biology of the Chelidae family, including ecology, anatomy, morphology, behavior, and other perspectives. Thus, this study aimed to answer questions related to reproduction and the factors that can affect the preparation, mating, sexual activity, and oviposition phases, highlighting the most researched areas and those that still require attention for the conservation of these species. Full article

The Chiuchiu Pond (CCP) is an inland brackish water body in a pre-Andean scenery in the Atacama Desert, northern Chile. Presently unprotected, the CCP is attractive for tourism and a notable geosite for wildlife characterized by maintaining a fixed water level and chemical composition without surface inlets/outlets. This paper aims to characterize factors accounting for its perennial character by gathering climatic, hydrogeochemical, and morphometric information and microbiological and functional characterization. The CCP is an isolated U-shaped doline with a maximum depth of 17.5 m and vertical walls with more than 80% of soluble salts (halite and calcite) under arid conditions characterized by constant seasonal variation patterns. This is a unique case in that no similar conditions among reported wetlands or ponds have been found in the world. From our studies, it was characterized as an oligotrophic, lentic oligomictic, well-mixed water body, without thermal stratification, stable water level and hydrochemical composition, with water balance conditions from underground flows. Analysis of the microbial community revealed a core composition dominated by Proteobacteria (43.1%), Bacteroidetes (23.5%), and Cyanobacteria (10%). We provide a multidisciplinary contribution to justify urgent actions for the CCP’s conservation, representing a model for other unprotected coastal and inland wetlands in northern Chile and drylands elsewhere. Full article