Hydrobiology, Volume 5, Issue 1 (March 2026) – 5 articles

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