''Apareiodon affinis'', the darter characine, is a species of fresh water

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

native to the

Río de la Plata Basin The Río de la Plata basin (, ), more often called the River Plate basin in scholarly writings, sometimes called the Platine basin or Platine region, is the Hydrography, hydrographical area in South America that drains to the Río de la Plata. I ...

in southern Brazil, Paraguay and northern Argentina.

Description

The darter characine is a small, fusiform fish growing to a maximum length of . Like other characids, it has a mouth on the underside of the head with a poorly developed upper lip. There are no dentary teeth and the pectoral fins have a single, unbranched fin-ray which the fish uses to prop itself up on the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

Ecology

The darter characine is an open water fish, and was one of several fish species in a reservoir on the

Paraná River The Paraná River ( ; ; ) is a river in south-central South America, running through Brazil, Paraguay, and Argentina for some ."Parana River". Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. ...

to thrive when large submerged

macrophyte Aquatic plants, also referred to as hydrophytes, are vascular plants and non-vascular plants that have adapted to live in aquatic environments ( saltwater or freshwater). In lakes, rivers and wetlands, aquatic vegetations provide cover for aquat ...

s were removed. The diet consists of

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

and the

periderm Bark is the outermost layer of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and consists ...

of aquatic vegetation, perhaps removed accidentally while the fish scrapes off the algae. The

karyotype A karyotype is the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is discerned by de ...

of this fish varies between populations. In the Upper Paraná basin, the sexes have distinct

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

numbers, the males showing 2n = 54 and the females 2n = 55. They have a multifactorial

ZW sex-determination system The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatwor ...

where the female is determined by ZW₁W₂ and the male by ZZ. In the separate Cuiabá River system, all individuals show 2n = 54. This is a non-migratory species and its reproductive strategy involves external fertilisation and a lack of parental care of eggs or young.

References

{{Taxonbar, from=Q6421527 Parodontidae Taxa named by Franz Steindachner Fish described in 1879