The Danube River has a large hydrographical basin, being the second largest river in Europe. The main channel flows through seven European countries with many species of fish inhabiting it. In this review we focused on the invasive species silver carp (Hypophthalmichthys molitrix), which plays an important ecological and economic role in its original habitat, but since introduced in Europe’s rivers, the species has posed a serious ecological risk under global warming. In this review paper, we gathered data regarding silver carp, such as when and how it entered the Danube Delta and the water temperature suitable for its growth and reproduction, mainly in the context of global warming, as well as the nature of nutrition and the ecological risk the species poses.

Microplastics (plastic particles < 5 mm) are ubiquitous pollutants that have the ability to carry microbiota, including pathogens. Microbial adhesion is usually a sign of pathogenicity; thus, we investigated the adherent microbiota found on 4 mm nylon strips, which were ingested and excreted by wild fish specimens. Retention times were recorded and the polymer analysis of the excreted samples was performed, which showed no signs of degradation, nor did their controls, represented by the nylon strips submerged in the same water tanks. Both the ingested samples and controls presented pathogens in large quantities. Following Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight identification, the dominant genus was represented by Aeromonas, revealing the fact that nylon microplastics can serve as undegradable physical carriers for this pathogen, among others, in the aquatic environment.

Plastic debris is considered an emerging aquatic pollutant as an alarming number of reports are indicating the environmental contamination with such agents. Ichthyofauna has been subjected to increasing plastic pollution over the past years, which has led to detrimental effects in the food chain, and consequently to the general health of ecosystems. In this study, we exposed juvenile specimens of Oreochromis niloticus to polyvinyl chloride (PVC) in powder form. Specimens and water parameters were closely monitored for 40 days before tissue samples were collected for histological and biochemical analysis. Structural hepatic alterations were observed in specimens from the exposed groups, such as intercellular corridors, dilation of sinusoidal capillaries, hyperchromatic nuclei, nuclear hypertrophy, and cytoplasm vacuolization. Low catalase activity was observed in the case of 1000 mg of PVC/kg feed group, as well as high levels of malondialdehyde compared to the control group, indicating oxidative stress. Glutathione peroxidase activity was also significantly decreased in the 500 and 1000 mg/kg feed group compared to the control group. These findings suggest that a midterm exposure to PVC particles can significantly affect the activity of antioxidative enzymes in O. niloticus specimens and induce changes of hepatic tissue structure.

Sturgeon species have inhabited the world’s seas and rivers for more than 200 million years and hold significant taxonomic significance, representing a strong conservation interest in aquatic biodiversity as well as in the economic sector, as their meat and eggs (caviar) are highly valuable goods. Currently, sturgeon products and byproducts can be legally obtained from aquaculture as a sustainable source. Intensive farming practices are accompanied by parasitic infestations, while several groups of parasites have a significant impact on both wild and farmed sturgeons. The present article is a review of common sturgeon parasites from the genus: Protozoa, Trematoda, Crustacea, Nematodes, Monogenea, Hirudinea, Copepoda, Acanthocephala, Cestoda, Polypodiozoa, and Hyperoartia, while also addressing their pathology and statistical distribution.

The present research was conducted within the framework of a broader investigation with the objective of identifying freshwater parasites and bacteria on national territory, with the aim of gaining a deeper understanding of the relationships between parasites, hosts, and the environment, and to assess the potential detrimental effects of parasitic infestation on the conservation status of fish populations. Within this study, it was documented the first recordings of parasites Vorticella globularia and Epistylis sp. in the Romanian Petro-leuciscus borysthenicus celensis fish species. A total of 42 specimens were collected from the Gurban River to study their infestation status, focusing on the skin, gills, and fins. From the samples analyzed, 16 specimens presented signs of infestation with five distinct parasite species (Ichthyophthirius multifiliis, Dactylogyrus vastator, Trichodina acuta, Vorticella globularia and Epistylis sp) and four bacterial strains (Aeromonas veronii, Shewanella putrefaciens, Aeromona hydrophila, and Citrobacter freundii). The results indicate that the skin is the organ most severely impacted by parasites and bacteria, followed by the gills. The fins, on the other hand, are the least susceptible to infection. Furthermore, the significant amount of parasitic infestation coupled with the high bacterial load of Aeromonas veronii indicates a plausible link between the two.

Sturgeon aquaculture is an important continuously developing sector within freshwater aquaculture and its sustainability is one of the most pressing matters nowadays. Thus, the urge to apprehend the mechanics of sturgeon growth in captivity as well as in nature is of immediate importance, considering the increase in customers’ requests for captive-grown sturgeon meat, caviar, and adjacent by-products. The present study evaluates several canonical growth indices in a controlled, indoor environment that included fluctuations in temperature, dissolved oxygen saturation, and ponderal density (g/L), known to affect sturgeon growth performance. Over the 91 days of evaluation, no significant correlation was found between the weight gain and the ponderal density, dissolved oxygen values, and temperature, among the 4 tanks used in the experiment setup, indicating, along with the lack of significant variance for the RCI per tank, that the growth observed is correlated only with the fodder fed to the fish.