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Successful invasive non-native fish species can cause enormous damage to native biodiversity. In mainland Europe, the introduction of the gibel carp (Carassius gibelio) has led to a decline in populations of the formerly widespread native crucian carp (C. carassius). Both invasive and native species develop two phenotypes, namely stunted and deep-bodied, which depend on the intensity of competition and predation in the water body. The deep-bodied phenotype is associated with a more diverse fish community composition, can attain large sizes and is very attractive to recreational anglers. This study analysed trends in the record sizes of native crucian carp and invasive gibel carp (individuals close to the maximum attainable size of the species) reported by recreational anglers over the last 50 years in Czechia, recording the invasion of gibel carp from its beginnings to the fully established population phase. The study provides circumstantial evidence that gibel carp is behind transition from the relative abundance of large crucian carp to near extirpation, while large gibel carp have taken over the reports of record catches in the genus Carassius. This indicates that the crucian carp, which is currently classified as critically endangered in the Red List of Czechia, has very limited possibilities to realise its deep-bodied phenotype. It also shows the potential of using data from recreational anglers for mapping invasion processes and as a source of relatively localised information on endangered species. [ABSTRACT FROM AUTHOR]

Fishes of the genus Carassius are useful experimental vertebrate models for the study of evolutionary biology and cytogenetics. Carassius demonstrates diverse biological characteristics, such as variation in ploidy levels and chromosome numbers, and presence of microchromosomes. Those Carassius polyploids with ≥ 150 chromosomes have microchromosomes, but the origin of microchromosomes, especially in European populations, is unknown. We used cytogenetics to study evolution of tandem repeats (U1 and U2 small nuclear DNAs and H3 histone) and microchromosomes in Carassius from the Czech Republic. We tested the hypotheses whether the number of tandem repeats was affected by polyploidization or divergence between species and what mechanism drives evolution of microchromosomes. Tandem repeats were found in tetraploid and hexaploid Carassius gibelio , and tetraploid Carassius auratus and Carassius carassius in conserved numbers, with the exception of U1 small nuclear DNA in C. auratus. This conservation indicates reduction and/or loss in the number of copies per locus in hexaploids and may have occurred by divergence rather than polyploidization. To study the evolution of microchromosomes, we used the whole microchromosome painting probe from hexaploid C. gibelio and hybridized it to tetraploid and hexaploid C. gibelio , and tetraploid C. auratus and C. carassius. Our results revealed variation in the number of microchromosomes in hexaploids and indicated that the evolution of the Carassius karyotype is governed by macrochromosome fissions followed by segmental duplication in pericentromeric areas. These are potential mechanisms responsible for the presence of microchromosomes in Carassius hexaploids. Differential efficacy of one or both of these mechanisms in different tetraploids could ensure variability in chromosome number in polyploids in general. [ABSTRACT FROM AUTHOR]

The crucian carp (Carassius carassius, L.) and the brown trout (Salmo trutta, L.) are vanishing from freshwater ecosystems of central Europe. To conserve both species, tailor‐made conservation management of habitats and populations of both species was implemented and tested in the Czech Republic (central Europe). This management was adjusted to reflect the ecological needs of both species. This study aimed to describe the results of a tested in situ management and to analyze the population growth of brown trout and crucian carp under ideal conditions. An experiment was performed at 14 small gravel pit lakes. Seven of them were adjusted to fit the crucian carp habitat requirements while the other seven were treated as a control group. The same experiment was done on 14 smaller streams and with brown trout. The occurrence and growth of crucian carp and brown trout were surveyed over 2 years. A significantly faster growth of both crucian carp and brown trout was observed on the adjusted lakes and streams in comparison to the control group ones. Trout and carp prospered on small streams and gravel pit lakes (respectively) that were free of angling, fish stocking, pollution, piscivorous predators, and competition with hybridizing species like Prussian carp (Carassius auratus, L.) or hatchery‐reared brown trout. [ABSTRACT FROM AUTHOR]

Morphometric and genetic variation were examined in parental Carassius auratus gibelio and Carassius carassius individuals, and their natural hybrids. Of meristic traits, only the number of gill rakers clearly distinguished hybrids (39·4 ± 1·4) from parental C. a. gibelio (48·3 ± 0·7) and C. carassius (28·6 ± 1·1). MtDNA sequences showed that the hybrids were descendants of female C. a. gibelio. Microsatellite analysis confirmed the presence in hybrids of variants typical of C. a. gibelio and C. carassius. [ABSTRACT FROM AUTHOR]