Investigation of extragonadal teratomas in two Poecilia wingei.

Teratoma is a rare tumour in fish consisting of tissues from more than one germ layer, that may be located in either the gonads or extragonadal sites. Teratomas in many fish species remain poorly understood. In this work, we performed the first histological examinations of extragonadal teratomas in Poecilia wingei and also examined the influence of a large teratoma on male sexual activity. The studied teratomas shared general organizational features, but they also had variations in both external and internal features. In teratomas, the most common and highly differentiated tissues were striated muscle and nervous tissue. Despite the tumour, the male P. wingei exhibited normal mating behaviour and retained the ability for successful copulation. The structural features of extragonadal teratomas in guppy fish indicate a possible connection between these tumours and a failure of conserved processes operating in the embryonic germline.

The role of thyroid hormones in the development of coloration of two species of Neotropical cichlids.

Neotropical cichlids demonstrate an enormous diversity of pigment patterns, a morphological trait that plays an important role in adaptation and speciation. It has been suggested that alterations of the activity of the thyroid axis, one of the main endocrine axes regulating fish ontogeny, are involved in the development and diversification of pigment patterns in Neotropical cichlids. To test this hypothesis, we assessed thyroid hormone developmental dynamics and pigment patterning, and experimentally induced hyperthyroidism and hypothyroidism at different developmental stages in the convict cichlid, Amatitlania nigrofasciata, and blue-eye cichlid, Cryptoheros spilurus. We found that the two species display a similar type of coloration development and similar reactions to changes of thyroid hormone level, but species-specific differences in hormonal dynamics and thyroid hormone responsiveness. These findings indicate that thyroid hormone is a necessary but not sufficient signal to induce the transition from larval to juvenile coloration, and is a component of a complex, concerted endocrine cascade that drives skin development.

Chromosome complements of Channalucius and C.striata from Phu Quoc Island and karyotypic evolution in snakehead fishes (Actinopterygii, Channidae).

Snakehead fishes of the family Channidae are obligatory air-breathers freshwater predators, the vast majority of which belong to the genus Channa Scopoli, 1777. Channa species are characterized by high karyotypic diversity due to various types of chromosomal rearrangements. It is assumed that, in addition to the lifestyle, fragmentation and isolation of snakehead populations contribute to an increase in karyotypic diversity. However, the chromosome complements of many isolated populations of widespread Channa species remain unknown, and the direction of karyotype transformations is poorly understood. This paper describes the previously unstudied karyotypes of Channalucius (Cuvier, 1831) and C.striata (Bloch, 1793) from Phu Quoc Island and analyzes the trends of karyotypic evolution in the genus Channa. In C.lucius, the karyotypes are differed in the number of chromosome arms (2n = 48, NF = 50 and 51), while in C.striata, the karyotypes are differed in the diploid chromosome number (2n = 44 and 43, NF = 48). A comparative cytogenetic analysis showed that the main trend of karyotypic evolution of Channa species is associated with a decrease in the number of chromosomes and an increase in the number of chromosome arms, mainly due to fusions and pericentric inversions. The data obtained support the assumption that fragmentation and isolation of populations, especially of continental islands, contribute to the karyotypic diversification of snakeheads and are of interest for further cytogenetic studies of Channidae.

Experimental evidence of the role of heterochrony in evolution of the Mesoamerican cichlids pigment patterns.

The Mesoamerican cichlids display a spectacular diversity of pigment patterns, which serve a variety of functions and serve as a strong selective trait for this lineage. The development and variation of coloration in the Mesoamerican cichlids have been detailed by several groups. In particular, Rícan, Musilová, Muska, and Novák () and Rícan, Piálek, Dragová, and Novák () determined homology of pattern and revealed four alternative types of coloration and their ontogeny. In this work, this group posed an "ontogenetic timing hypothesis" proposing heterochronic shifts underlying major transitions in the evolution of the Mesoamerican cichlids. Here, we experimentally test this hypothesis by experimentally altering timing of pigment pattern formation in the convict cichlid Amatitlania nigrofasciata, a member of the Mesoamerican cichlids, via manipulations of thyroid hormone (TH) function. The response of different pigment cell lineages to TH-perturbations revealed that the transition from larval to juvenile coloration in the convict cichlid is under the control of TH-signaling. Importantly, hormonally induced changes in the timing of pigment cell lineages' development resulted in shifts of coloration ontogeny type observed between lineages and led to the appearance of phenotypes mimicking those in phylogenetically close and distant species. Thus, our findings support the hypothesis that simple changes in ontogenetic timing underlies species specific patterns in pigmentation and provide new perspectives for studying the role of endocrine signaling in the evolution of cichlids.