Reliable assessment of the ecological status of standing waters is key for the effective implementation of the Water Framework Directive and for supporting water management and conservation. Biological quality elements, including benthic macroinvertebrates, provide an integrated measure of ecological condition by reflecting the cumulative impacts of environmental pressures over time. However, assessment methods developed for running waters are not readily applicable to standing waters, highlighting the need for category-specific approaches. We conducted a large-scale survey of representative stagnant water bodies (lakes and reservoirs) on the territory of Bulgaria. The goal was to develop a relevant type-specific methodology for the ecological status assessment of standing waters based on macrozoobenthos. We sampled 79 monitoring lake sites between May and November 2020 through an adapted version of the multi-habitat sampling methodology developed within the European AQEM/STAR projects in accordance with applicable standards. A composite sample was taken from the littoral zone of lakes and reservoirs, representative of the substrates available at each location. The sites represent 19 lake types. Eleven biological indices for lakes and seven for rivers were calculated in order to identify the most suitable metric. For each of the metrics, the pressure–response relationship was estimated. Being the first operational national index based on macroinvertebrates, the proposed Bulgarian multi-metric index for lakes is an adapted version of the Hungarian multi-metric macroinvertebrate index. It consists of three metrics, which have been separately tested in Bulgaria for monitoring purposes as early as 2011–2012 as well as in subsequent scientific research. Ecological quality class boundaries for each type of water body were determined. The compatibility of the BMMI with the existing national monitoring programme would facilitate its future integration into the biological water assessment system.
Liobagrus (Siluriformes: Amblycipitidae) is a taxonomically challenging genus of torrent catfishes. Its morphological diagnoses are unstable and species boundaries contentious. Here, the complete mitochondrial genomes of two L. aequilabris individuals were sequenced, characterized, and compared with congeneric mitogenomes. The mitogenomes are double-stranded, circular molecules exhibiting the typical vertebrate organization (13 PCGs, 2 rRNAs, 22 tRNAs, and a control region), an AT-rich composition, and evidence of strong purifying selection (Ka/Ks < 1) across all PCGs, with codon-level analysis detecting episodic positive selection at only a few sites, mainly in ND4 and ND5. Maximum likelihood and Bayesian inference trees recovered Liobagrus as monophyletic, comprising two strongly supported clades: Clade I (Korea and Japan) and Clade II (Korea and northern China, subclade A; Yangtze and southeastern coastal species, subclade B). Within subclade B, the terminal assemblage of L. aequilabris and its close relatives remains poorly resolved; the two trees are topologically equivalent and differ only in displayed orientation, representing no genuine conflict. Among the nominal species examined here, conspecificity and misidentification warrant priority testing, although recent divergence (including rapid radiation with incomplete lineage sorting) and mitochondrial introgression cannot be excluded with mitochondrial data alone, underscoring the need for integrative taxonomy based on nuclear/genome-wide markers and voucher-based identification. The mitogenomes provide a molecular reference of L. aequilabris for future population, eDNA, and conservation studies.
Dietary lipid sources influence growth, tissue nutrient composition, and physiological responses in aquatic animals, but their effects on female broodstock abalone remain insufficiently understood. This study evaluated the effects of five dietary lipid sources, including fish oil, perilla seed oil, safflower oil, olive oil, and lard, on growth performance, foot muscle nutritional quality, digestive-gland antioxidant status, and survival following Vibrio harveyi AP37 challenge in female broodstock Haliotis discus hannai. A total of 500 female abalone were randomly assigned to five dietary treatments, with four replicates per treatment, and fed isonitrogenous and isolipidic diets for 90 days. Results showed that the dietary lipid source significantly affected growth, foot muscle crude protein and lipid contents, amino acid and fatty acid compositions, and digestive-gland antioxidant status. The fish oil group showed the highest measured total amino acid and taurine contents and docosahexaenoic acid (DHA) proportion in foot muscle, together with the highest observed final survival after V. harveyi challenge. Perilla seed oil and olive oil warrant further evaluation as alternative supplemental lipid sources under the present experimental conditions. These findings provide useful information for lipid source selection in formulated diets for female broodstock abalone.
This study aimed to compare the effects of three brewer’s yeast-derived immunostimulants—an autolyzed yeast containing nucleotides (AY), a highly purified 1,3/1,6-β-glucan (PB), and a yeast cell wall product containing mannan-oligosaccharides (YCW)—on the growth performance and health status of juvenile Pacific white shrimp (Penaeus vannamei). An 8-week growth trial was conducted for shrimp (initial body weight 1.83 ± 0.01 g), fed with diets supplemented with 0.1% AY, 0.015% PB, and 0.1% YCW, respectively. Growth performance, serum biochemical parameters, tissue morphology, immune gene expression and gut microbiota were assessed, followed by a Vibrio parahaemolyticus challenge trial. The results showed that AY and YCW groups achieved growth performance comparable to the control group, while PB exhibited a numerically lower weight gain rate than the other groups (p > 0.05). Serum biochemical analysis indicated that AY and YCW significantly reduced aspartate aminotransferase activities relative to the control (p < 0.05), while dietary AY tended to elevate serum protein, albumin, globulin, triglycerides, and cholesterol levels (p > 0.05). In addition, AY optimized hepatopancreatic and intestinal morphology. Dietary PB significantly upregulated the expression of hepatopancreatic antioxidant and inflammatory genes (SOD, TGF-β1) and suppressed the intestinal abundance of Vibrio (p < 0.05). The challenge test showed a marginally higher 3-day post-challenge survival of PB (76.7%) and AY (73.3%) than that of controls (53.3%) (p < 0.1), and PB retained the highest survival on day 7. Collectively, these findings reveal the three yeast-derived ingredients are functionally distinct immunostimulants: AY (nucleotide-rich autolysate) serves as a growth-compatible and gut–heptopancreas restorative additive supporting regular grow-out periods; YCW (mannan-oliosacchaides-rich cell wall) acts as a microbiota-modulating gut barrier enhancer for long-term intestinal health; and PB (purified β-glucan) activates hepatic antioxidant and immune pathways for superior short-term disease resistance. These findings highlight that immunostimulant choice in shrimp should be matched to production phase and disease-risk context.
Reliable fish cell models are essential for studying cellular processes under controlled in vitro conditions and thereby reducing the need for animal experiments. In this study, we established and characterized OMYlar5, a novel larval cell line derived from rainbow trout (Oncorhynchus mykiss). OMYlar5 demonstrated sustained proliferative capacity over at least 60 passages, indicating spontaneous immortalization and its suitability for long-term applications in fish biology and aquaculture research. To investigate temperature-dependent cellular responses, cells were cultured at 18, 20, and 22 °C, and changes in growth, morphology, cytoskeletal organization, stress responses, and gene expression were analyzed. Increased temperature enhanced cell proliferation, whereas the expression of the proliferation-associated genes pcna and c-myc remained unchanged. Temperature-dependent alterations in cell morphology and F-actin organization were observed, with enhanced actin bundle formation at 22 °C. However, no significant induction of Hsp70 or Hsp90 was detected at the transcript or protein level, suggesting that the tested temperature range was not associated with detectable induction of these heat shock proteins. Furthermore, OMYlar5 cells expressed nanog, nes, pax3, and sox9, whereas pou5f1 and sox2 were expressed at very low levels. These expression patterns provide information on the molecular characteristics of the cell line. Overall, OMYlar5 may provide a useful in vitro model for investigating temperature responses, cellular physiology, and developmental processes in rainbow trout.
