Effects of Schyzocotyle acheilognathi (Yamaguti, 1934) infection on the intestinal microbiota, growth and immune reactions of grass carp (Ctenopharyngodon idella)

Host-Microbiota-Parasite Interactions in Grass Carp: Insights from Ichthyophthirius multifiliis Infection

The ciliate parasite Ichthyophthirius multifiliis poses significant threats to grass carp (Ctenopharyngodon idellus) aquaculture. However, the limited understanding of host microbiota shifts and immune responses hinders effective control strategies. This study integrated analyses of host pathological indices, immune response and skin/gill/gut microbiota shifts after I. multifiliis infection. A histopathological examination identified gill and fin tissues embedded with I. multifiliis, accompanied by epithelial necrosis, and inflammatory cell infiltration. Biochemical profiling revealed marked elevations in aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea (UREA), and creatinine (CREA) levels, indicating impaired hepatic and renal function. Quantitative RT-PCR analyses demonstrated the up-regulation of mucosal immune gene IgT and pro-inflammatory cytokine TNF-α while increasing the trend of systemic immune gene IgM. 16S rRNA sequencing revealed significant reductions in skin microbiota diversity. At the genus level, opportunistic pathogens Aeromonas and Vibrio proliferated in the intestine, whereas Flavobacterium and Candidatus Megaira increased in the skin and gills. Correlation analyses identified positive associations between Aeromonas/Vibrio abundance and host phenotype, contrasting with negative correlations observed for Sphingomonas, Acinetobacter, and Leifsonia. These findings demonstrate that I. multifiliis infection induces host microbiome dysbiosis and potentially opportunistic bacterial infections. This investigation advances our understanding of tripartite host-microbiota-parasite interactions and supports microbial community-based parasitosis control in fish culture.

Glandular cell products in adult cestode: A new tale of tapeworm interaction with fish innate immune response

The caryophyllidean tapeworm Caryophyllaeus brachycollis (Janiszewska, 1953) is indigenous to the Lake Blidinje in the west-central part of Bosnia-Herzegovina where it infects chub Squalius tenellus (Heckel, 1843). Of 22 chubs examined, 45% were infected with C. brachycollis and a total of 912 specimens of this worm were counted. Histopathological and ultrastructural investigations were conducted on interface region between chub intestine and cestode scolex. Different sizes of lipid droplets in cestode tegument, in interface region and in chub enterocytes were observed. C. brachycollis lacks any specialized attachment organs and with an expanded, flattened scolex goes deep in mucosal folds and firmly attaches to them. In the epithelium of fish intestine, near the site of worm attachment, a high number of mucous cells and several rodlet cells were noticed. Indeed, within the intestinal tunica propria-submucosa, beneath the site of scolex attachment, numerous neutrophils and mast cells were encountered. Transmission electron microscopy of the apical part of the scolex of C. brachycollis showed the occurrence of a multicellular, syncytial glandular complex, the scolex produced membrane-bound secretory granules and their fibrillar contents discharged by merocrine and apocrine secretion onto the host-parasite interface. Our results are among the first to provide evidence on the sophisticated relationship between fish intestine and amorphous-undefinable substance produced by scolex glandular complex.

Parasites and Pollutants: Effects of Multiple Stressors on Aquatic Organisms

Parasites can affect their hosts in various ways, and this implies that parasites may act as additional biotic stressors in a multiple-stressor scenario, resembling conditions often found in the field if, for example, pollutants and parasites occur simultaneously. Therefore, parasites represent important modulators of host reactions in ecotoxicological studies when measuring the response of organisms to stressors such as pollutants. In the present study, we introduce the most important groups of parasites occurring in organisms commonly used in ecotoxicological studies ranging from laboratory to field investigations. After briefly explaining their life cycles, we focus on parasite stages affecting selected ecotoxicologically relevant target species belonging to crustaceans, molluscs, and fish. We included ecotoxicological studies that consider the combination of effects of parasites and pollutants on the respective model organism with respect to aquatic host-parasite systems. We show that parasites from different taxonomic groups (e.g., Microsporidia, Monogenea, Trematoda, Cestoda, Acanthocephala, and Nematoda) clearly modulate the response to stressors in their hosts. The combined effects of environmental stressors and parasites can range from additive, antagonistic to synergistic. Our study points to potential drawbacks of ecotoxicological tests if parasite infections of test organisms, especially from the field, remain undetected and unaddressed. If these parasites are not detected and quantified, their physiological effects on the host cannot be separated from the ecotoxicological effects. This may render this type of ecotoxicological test erroneous. In laboratory tests, for example to determine effect or lethal concentrations, the presence of a parasite can also have a direct effect on the concentrations to be determined and thus on the subsequently determined security levels, such as predicted no-effect concentrations. Environ Toxicol Chem 2023;42:1946-1959. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Freshwater as a Sustainable Resource and Generator of Secondary Resources in the 21st Century: Stressors, Threats, Risks, Management and Protection Strategies, and Conservation Approaches

This paper is a synthetic overview of some of the threats, risks, and integrated water management elements in freshwater ecosystems. The paper provides some discussion of human needs and water conservation issues related to freshwater systems: (1) introduction and background; (2) water basics and natural cycles; (3) freshwater roles in human cultures and civilizations; (4) water as a biosphere cornerstone; (5) climate as a hydrospheric 'game changer' from the perspective of freshwater; (6) human-induced stressors' effects on freshwater ecosystem changes (pollution, habitat fragmentation, etc.); (7) freshwater ecosystems' biological resources in the context of unsustainable exploitation/overexploitation; (8) invasive species, parasites, and diseases in freshwater systems; (9) freshwater ecosystems' vegetation; (10) the relationship between human warfare and water. All of these issues and more create an extremely complex matrix of stressors that plays a driving role in changing freshwater ecosystems both qualitatively and quantitatively, as well as their capacity to offer sustainable products and services to human societies. Only internationally integrated policies, strategies, assessment, monitoring, management, protection, and conservation initiatives can diminish and hopefully stop the long-term deterioration of Earth's freshwater resources and their associated secondary resources.