Pikeperch (Sander Lucioperca) belongs to main predatory fish species in freshwater bodies throughout Europe playing the key role by reducing planktivorous fish abundance. Two size classes of the young-of-the-year (YOY) pikeperch are known in Europe and North America. Our long-term fish survey elucidates late-summer size distribution of YOY pikeperch in the Lipno Reservoir (Czechia) and recognizes two distinct subcohorts: smaller pelagic planktivores heavily outnumber larger demersal piscivores. To explore molecular mechanisms accompanying the switch from planktivory to piscivory, we compared brain transcriptomes of both subcohorts and identified 148 differentially transcribed genes. The pathway enrichment analyses identified the piscivorous phase to be associated with genes involved in collagen and extracellular matrix generation with numerous Gene Ontology (GO), while the planktivorous phase was associated with genes for non-muscle-myosins (NMM) with less GO terms. Transcripts further upregulated in planktivores from the periphery of the NMM network were Pmchl, Pomcl, and Pyyb, all involved also in appetite control and producing (an)orexigenic neuropeptides. Noncoding RNAs were upregulated in transcriptomes of planktivores including three transcripts of snoRNA U85. Thirty genes mostly functionally unrelated to those differentially transcribed were alternatively spliced between the subcohorts. Our results indicate planktivores as potentially driven by voracity to initiate the switch to piscivory, while piscivores undergo a dynamic brain development. We propose a spatiotemporal spreading of juvenile development over a longer period and larger spatial scales through developmental plasticity as an adaptation to exploiting all types of resources and decreasing the intraspecific competition.

• Klíčová slova
• (Sander (Stizostedion) lucioperca), brain transcriptome, cannibalism, developmental plasticity, heterochrony, snoRNA,
• MeSH
• alternativní sestřih * MeSH
• genetická transkripce MeSH
• mozek * metabolismus   MeSH
• nekódující RNA genetika   metabolismus   MeSH
• okounovití genetika   fyziologie   MeSH
• regulace genové exprese fyziologie   MeSH
• stravovací zvyklosti MeSH
• transkriptom * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• nekódující RNA MeSH

The main objective of this study was to elucidate whether there are any effects of sperm dilution time before short-term storage in common carp. The sperm of five males (2-2.5 kg body weight, 3 years old) with good spermatozoa motility (˃90 %) were diluted with carp extender immediately, 3 h post-diluted, and undiluted fresh sperm was used as control. Sperm motility and velocity of undiluted and diluted sperm were evaluated using a CASA system. A two-way ANOVA revealed that spermatozoa motility, curvilinear velocity (VCL), and straight-line velocity (VSL) were significantly impacted by storage time, varying dilution with extenders, and their interaction (p < 0.001). Sperm motility and velocity dropped steadily with increasing storage periods for diluted sperm, while they drastically fell for undiluted sperm and became immotile at 5 days post-storage. In the control group, the mean percentage of sperm motility was achieved by 40.60 % at 3 days post-storage and sperm diluted with Cejko solution immediately and 3 h post-diluted sperm retained motility at 65.13 % and 65.63 %, respectively, at 3 days post-storage and retained motility of 39.45 and 40.43 %, respectively, at 7 days post-storage. After 7 days post-storage, the diluted (immediately and 3 h post-diluted) pooled sperm had a 61.01 % and 56.70 % fertilization and a 43.40 % and 36.52 % hatching rate, whereas fresh sperm had an 89.34 % fertilization and 78.06 % hatching success. According to the results of the fertilization and hatching assay, compared to fresh sperm, 7 days of stored diluted pooled sperm produced a 68.29 % fertilization rate and a 55.60 % hatching rate.

• Klíčová slova
• Common carp, Fertilization, Hatching, Malformations, Spermatozoa motility, Spermatozoa velocity,
• MeSH
• analýza spermatu veterinární   MeSH
• časové faktory MeSH
• fertilizace fyziologie   MeSH
• kapři * fyziologie   MeSH
• motilita spermií * fyziologie   MeSH
• spermie * fyziologie   MeSH
• uchování spermatu * veterinární   metody   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

The Iberian Peninsula, in southwestern Europe, is home to a distinctive freshwater fish fauna, predominantly composed of endemic species. This is a consequence of the prolonged isolation from western Europe caused by the Pyrenees, the diverse geological and climatic gradients, and the isolation of river basins. Freshwater and diadromous fishes have diversified in the Iberian Peninsula and include 72 currently recognized native species, 50 of which are endemic to the region. Habitat loss and degradation, the introduction of invasive species, and climate change have placed Iberian freshwater and diadromous fishes among the most threatened groups of vertebrates, with some species on the brink of extinction. Here, we present 60 new complete mitochondrial genome assemblies out of the 109 freshwater and diadromous fish species found in the Iberian Peninsula, including the mitogenomes of 37 endemics. These resources are crucial for characterising the mitochondrial evolution of species, reconstructing phylogeny and paleogeography, advancing species identification, delineation, and monitoring, and ultimately supporting conservation planning.

• MeSH
• fylogeneze * MeSH
• genom mitochondriální * MeSH
• ryby * genetika   klasifikace   MeSH
• sladká voda * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• dataset MeSH
• Geografické názvy
• Španělsko MeSH

Subclass Elasmobranchii belongs to an old evolutionary class of Chondrichthyes that diverged 450 mya, presenting a wide diversity of reproductive strategies while preserving the ancient mode of internal fertilization. Despite such evolutionary success, many species in this group are at serious risk of extinction. Understanding the principles of sperm progressive motility and physiology of such an ancient group of vertebrates is crucial for advancing future assisted reproductive techniques to safeguard this species and for deepening our understanding of the evolution of reproduction. Elasmobranchii species possess big spermatozoa (compared to bony fishes) with an elongated helical head and tail similar to one currently existing (but later diverged) in birds, reptiles, and amphibians, which can be considered an evolutionary ancient. These structures may be associated with the necessity to penetrate viscous ovarian fluid or the jelly layer of eggs, suggesting environmental viscosity as the driving pressure shaping large-sized sperm heads into helical shapes through evolution. We observed spermatozoa motility with high-speed video microscopy to capture sperm and flagellar motion in three Elasmobranchii species: the freshwater ray Potamotrygon motoro, the marine skate Raja asterias and the shark Scyliorhinus canicula. We investigated the effect of viscosity on spermatozoa motility parameters and its ability to break free from spermatozeugmata, move progressively, and perform directional changes. After 20 min of observation, the spermatozeugmata conserved their structure in a low viscosity media of 1000 mOsm/kg osmolality. In comparison, no remaining structure of spermatozeugmata could be found in high-viscosity media with 2% methylcellulose (MC) in all three species due to progressive spermatozoa motion. We find that spermatozoa's unique helical head-to-flagellum architecture is specific to promote locomotion in high-viscosity fluid; they cannot move progressively in low viscosity. The highest velocity for shark sperm was observed at 0.75% MC and 1% MC for ray and skate sperm. Viscosity stabilizes the flagellar propagation, producing rotational forces and allowing the helical head to "screw" into the media. Our observations suggest that the surrounding viscosity is critical to allowing spermatozoa progressive motility and enabling spermatozoa to control direction via newly observed head buckling in high viscosity. As such, the viscosity may be a key element controlling and regulating sperm performance and navigation during fertilization in the Elasmobranchii species.

• MeSH
• biologická evoluce MeSH
• Elasmobranchii fyziologie   anatomie a histologie   MeSH
• hlavička spermie fyziologie   MeSH
• motilita spermií * fyziologie   MeSH
• spermie * fyziologie   MeSH
• viskozita MeSH
• žraloci fyziologie   anatomie a histologie   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Iceland is an isolated, sub-Arctic, oceanic island of volcanic origin in the northern North Atlantic. With a limited faunal diversity and being the most northern point in the distributional range for some species, it is an intriguing model region to study parasite biodiversity and biogeography. Since 2006, there has been a history of intense biodiversity discoveries of freshwater trematodes (Trematoda, Digenea), thanks to the use of integrative taxonomic methods. The majority of digeneans (28 out of 41 known) were characterised with molecular genetic methods and morphological analyses, with some of their life-cycle stages and geographical distribution assessed. A surprising diversity has been discovered, comprising species of the families Allocreadiidae, Cyclocoeliidae, Diplostomidae, Echinostomatidae, Gorgoderidae, Plagiorchiidae, Notocotylidae, Schistosomatidae, and Strigeidae. Many of the recorded species complete their life cycles within Iceland, with three snail species (Ampullaceana balthica, Gyraulus parvus, Physa acuta) known as intermediate hosts. No trematodes endemic for Iceland were found; they appear to be generalists with wide geographical ranges dispersed mainly by migratory birds. Interestingly, fish trematodes recorded in Iceland were found in mainland Europe, indicating that they might be dispersed by anadromous fishes, by human activity, or by migratory birds carrying intermediate hosts. The trematode fauna is mainly Palaearctic, with few species recorded in North America. We highlight the ongoing need for precise species identification via integrative taxonomic methods, which is a baseline for any further ecological studies and adequate epidemiological and conservation measures. Also, there is still a need of obtaining well-preserved vouchers of adults for definite species delimitation.

• Klíčová slova
• Digenea, Gastropoda, Lymnaeidae, Planorbidae, cercariae,
• MeSH
• biodiverzita * MeSH
• hlemýždi parazitologie   MeSH
• infekce červy třídy Trematoda * parazitologie   veterinární   epidemiologie   MeSH
• ryby parazitologie   MeSH
• sladká voda * parazitologie   MeSH
• stadia vývoje MeSH
• Trematoda * klasifikace   genetika   izolace a purifikace   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Geografické názvy
• Island MeSH

Early life experiences have long-lasting effects on behaviour and physiology, influencing development of adaptive natural behaviours. Enriching farmed environments encourages expression of natural behaviours in captive fish, promoting positive animal welfare, important for conducting valid and reproducible research and informing better management practices. Using juvenile Atlantic Salmon (Salmo salar), we tested whether provision of environmental enrichment in early life improves welfare. Welfare indicators were measured comparing enriched to non-enriched tanks. Morphological (fin damage and body condition), physiological (plasma cortisol) and behavioural traits (activity, group cohesion, and neophobia) were recorded. Molecular expression of brain mRNA transcripts related to stress response, neuroplasticity and serotonergic system was analysed. Environmental enrichment did not affect morphological welfare indicators, activity, or cortisol. Enriched fish were more cohesive than non-enriched fish, less neophobic, with higher serotonergic turnover, suggesting enrichment mitigates against stress, promoting positive emotional states. Genes related to neuronal development and activity (bdnf and ndf1), cellular stress (hsp90 and hsp70), and serotonin synthesis (tph2) increased in enriched fish following stress, enhancing cognitive function. Our findings suggest early life environmental enrichment is advantageous for positive animal welfare by improving emotional states in captive environments, ensuring animals are free of negative experiences and able to access positive ones.

• Klíčová slova
• Cognitive abilities, Fish welfare, Neurogenesis, Social behaviour, Structural enrichment,
• MeSH
• chování zvířat * fyziologie   MeSH
• hydrokortison krev   metabolismus   MeSH
• pohoda zvířat * MeSH
• Salmo salar * fyziologie   genetika   růst a vývoj   MeSH
• vodní hospodářství * metody   MeSH
• životní prostředí MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• hydrokortison MeSH

This paper presents an approach to apply aquatic passive sampling (PS) in regulatory chemical water quality monitoring in Europe. Absorption-based passive sampling is well developed and suitable for the sampling of hydrophobic chemicals, some of which are European Water Framework Directive priority substances with Environmental Quality Standards (EQS) derived for biota. Considering a chemical activity approach to chemical risk assessment, we propose equilibrium concentration in lipids (from passive water sampling) as a reference value for measured concentrations in biota. Through existing PS-fish datasets, we show a growing body of evidence supporting the use of lipid-based contaminant concentrations at equilibrium with water derived from PS as a conservative proxy of levels of these chemicals in fish. We propose a procedure that includes PS as a first, animal-free screening step of a tiered approach, followed by more conventional fish analyses when PS indicates these are needed to confirm EQSbiota exceedance. This paper reviews fish-passive sampler datasets, provides a reasoning for the proposed procedure and discusses how to broadly put it into monitoring practice. PS offers the possibility of well-defined standardised monitoring approaches that can help overcome the natural variability challenges associated with measurements in biota across member states and simplify EQSbiota compliance.

• Klíčová slova
• Biota monitoring, EQS, Passive sampling, Priority substances, Silicone rubber, Tiered approach,
• MeSH
• chemické látky znečišťující vodu * analýza   MeSH
• hydrofobní a hydrofilní interakce * MeSH
• monitorování životního prostředí * metody   MeSH
• ryby * MeSH
• společenstvo MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Evropa MeSH
• Názvy látek
• chemické látky znečišťující vodu * MeSH

BACKGROUND: Parasitism as a life strategy has independently evolved multiple times within the eukaryotic tree of life. Each lineage has developed mechanisms to invade hosts, exploit resources, and ensure replication, but our knowledge of survival mechanisms in many parasitic taxa remain extremely limited. One such group is the Myxozoa, which are obligate, dixenous cnidarians. Evidence suggests that myxozoans evolved from free-living ancestors to endoparasites around 600 million years ago and are likely one of the first metazoan parasites on Earth. Some myxozoans pose significant threats to farmed and wild fish populations, negatively impacting aquaculture and fish stocks; one such example is Sphaerospora molnari, which forms spores in the gills of common carp (Cyprinus carpio), disrupting gill epithelia and causing somatic and respiratory failure. Sphaerospora molnari undergoes sequential development in different organs of its host, with large numbers of morphologically distinct stages occurring in the blood, liver, and gills of carp. We hypothesize that these parasite life-stages differ in regards to their host exploitation, pathogenicity, and host immune evasion strategies and mechanisms. We performed stage-specific transcriptomic profiling to identify differentially expressed key functional gene groups that relate to these functions and provide a fundamental understanding of the mechanisms S. molnari uses to optimize its parasitic lifestyle. We aimed to identify genes that are likely related to parasite pathogenicity and host cell exploitation mechanisms, and we hypothesize that genes unique to S. molnari might be indicative of evolutionary innovations and specific adaptations to host environments. RESULTS: We used parasite isolation protocols and comparative transcriptomics to study early proliferative and spore-forming stages of S. molnari, unveiling variation in gene expression between each stage. We discovered several apparent innovations in the S. molnari transcriptome, including proteins that are likely to function in the uptake of previously unknown key nutrients, immune evasion factors that may contribute to long-term survival in hosts, and proteins that likely improve adhesion to host cells that may have arisen from horizontal gene transfer. Notably, we identified genes that are similar to known virulence factors in other parasitic organisms, particularly blood and intestinal parasites like Plasmodium, Trypanosoma, and Giardia. Many of these genes are absent in published cnidarian and myxozoan datasets and appear to be specific to S. molnari; they may therefore represent potential innovations enabling Sphaerospora to exploit the host's blood system. CONCLUSIONS: In order to address the threat posed by myxozoans to both cultured fish species and wild stocks, it is imperative to deepen our understanding of their genetics. Sphaerospora molnari offers an appealing model for stage-specific transcriptomic profiling and for identifying differentially expressed key functional gene groups related to parasite development. We identified genes that are thus far unique to S. molnari, which reveal their evolutionary novelty and likely role as adaptations to specific host niches. In addition, we describe the pathogenicity-associated genetic toolbox of S. molnari and discuss the implications of our discoveries for disease control by shedding light on specific targets for potential intervention strategies.

• Klíčová slova
• Sphaerospora molnari, Differential expression, Myxozoans, Pathogenicity related, Species specific genes,
• MeSH
• fyziologická adaptace genetika   MeSH
• interakce hostitele a parazita genetika   MeSH
• kapři parazitologie   MeSH
• Myxozoa * genetika   patogenita   fyziologie   MeSH
• nemoci ryb parazitologie   MeSH
• stadia vývoje genetika   MeSH
• stanovení celkové genové exprese MeSH
• transkriptom * MeSH
• žábry parazitologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• srovnávací studie MeSH

During their radiation, certain groups of animals evolved significant phenotypic disparity (morphological diversity), enabling them to thrive in diverse environments. Adaptations to the same type of environment can lead to convergent evolution in function and morphology. However, well-documented examples in repeated adaptations of teleost fishes to different habitats, which are not primarily related to trophic specialization, are still scarce. Gobies are a remarkable fish group, exhibiting a great species diversity, morphological variability, and extraordinary ability to colonize very different environments. A variety of lifestyles and body forms evolved also in European lineages of gobies. We conducted two-dimensional geometric morphometric and phylomorphospace analyses in European lineages of gobies and evaluated the extent of convergent evolution in shape associated with adaptation to various habitats. Our analyses revealed the change in shape along the nektonic-cryptobenthic axis, from very slender head and body to stout body and wide head. We showed convergent evolution related to mode of locomotion in the given habitat in four ecological groups: nektonic, hyperbenthic, cryptobenthic, and freshwater gobies. Gobies, therefore, emerge as a highly diversified lineage with unique lifestyle variations, offering invaluable insights into filling of ecomorphological space and mechanisms of adaptation to various aquatic environments with distinct locomotion requirements.

• Klíčová slova
• Gobiiformes, convergent evolution, geometric morphometry, molecular dating, teleosts,
• MeSH
• biologická evoluce * MeSH
• ekosystém MeSH
• fylogeneze MeSH
• fyziologická adaptace MeSH
• Perciformes anatomie a histologie   genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Evropa MeSH

Salmonid fishes are a widespread and economically important group of fishes that are strongly affected by anthropogenic environmental degradation. Consequently, studies on their behavior and ecology are essential for their conservation. Wild Arctic grayling (Thymallus arcticus) were observed in an unimpacted Alaskan river using underwater video observations for two consecutive summers (2015 and 2016). Foraging, aggressive behavior, and position held by individual fish were quantified. Fish held focal positions in the water column most of the time (mean = 81%), active foraging was observed for 14% of the observation periods, and antagonistic interactions occurred during 5% of the time. The analysis of intraspecific aggression revealed that aggressive interactions occurred between conspecifics of similar sizes (±100 mm), although the winners of bouts were significantly larger than the losers. Notably, initiators emerged as more successful in these bouts compared to receivers, irrespective of body length. These findings underscore the significance of conducting field studies to gain valuable insights into the behavior of fish in their natural stream environments.

• Klíčová slova
• Alaska, aggression, behavior, stream fish, visual observation,
• MeSH
• agrese * MeSH
• řeky * MeSH
• Salmonidae * fyziologie   MeSH
• sociální dominance MeSH
• stravovací zvyklosti MeSH
• velikost těla * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Aljaška MeSH