Recent years have seen a global and rapid resurgence of fungal diseases with direct impact on biodiversity and local extinctions of amphibian, coral, or bat populations. Despite similar evidence of population extinction in European fish populations and the associated risk of food aquaculture due to the emerging rosette agent Sphaerothecum destruens, an emerging infectious eukaryotic intracellular pathogen on the fungal–animal boundary, our understanding of current threats remained limited. Long-term monitoring of population decline for the 8-year post-introduction of the fungal pathogen was coupled with seasonal molecular analyses of the 18S rDNA and histological work of native fish species organs. A phylogenetic relationship between the existing EU and US strains using the ribosomal internal transcribed spacer sequences was also carried out. Here, we provide evidence that this emerging parasite has now been introduced via Pseudorasbora parva to sea bass farms, an industry that represents over 400 M€ annually in a Mediterranean region that is already economically vulnerable. We also provide for the first time evidence linking S. destruens to disease and severe declines in International Union for Conservation of Nature threatened European endemic freshwater fishes (i.e. 80% to 90 % mortalities). Our findings are thus of major economic and conservation importance.
In this research the effects of oat Avena sativa extract on the non-specific immune system of common carp (Cyprinus carpio) was examined. For this purpose, the fishes (average weight 9.91 ± 1.52 g) were fed with 5 g kg À1 , 10 g kg À1 and 20 g kg À1 oat extract supplemented diets for 60 days. Following 60 days of feeding, the fishes were injected with Aeromonas hydrophila and mortalities were recorded. Lysozyme and myeloperoxidase activity, improved in all groups that received feed supplemented with oat extract. Serum glucose and cholesterol decreased while total protein and albumin in fish increased with the use of the diet supplement with oat extract. Haemoglobin (Hb), mean cell hemoglobin (MCH) and mean cell haemoglobin concentration (MCHC) increased with diet supplemented with oat extract. Oat extract at the concentration of 10 g kg À1 showed significantly higher relative percentage survival (67%) when compared with the control against A. hydrophila injection. Also the dietary supplementation with oat extract caused a significant increase in growth parameters (final weight (FW), weight gain (WG), specific growth rate (SGR) and feed conversion ratio (FCR), when compared to non-supplemented control basal diet. The results suggest that A. sativa extract can be used as a feed supplement to enhance fish immune response and disease resistance against A. hydrophila.
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