This species is euryhaline and mostly inhabits brackish estuaries, coastal lagoons and the lower reaches of rivers.

It also occurs in freshwater habitats, however, including a number of inland lakes in Sri Lanka although it appears to have been introduced intentionally.

The genus Apistogramma is among the most speciose of South American cichlid genera with around 70 species valid at present but many more awaiting description. In addition many species exist in two or more geographical colour forms which may or may not turn out to be distinct in the future. Hobbyists tend to label these with collection data if available in order to avoid mixing them and the potential of hybridisation.

Member species have also been organised into a series of species lineages, complexes and groups by authors in order to better separate them.

The genus Apistogramma is among the most speciose of South American cichlid genera with around 70 species valid at present but many more awaiting description. In addition many species exist in two or more geographical colour forms which may or may not turn out to be distinct in the future. Hobbyists tend to label these with collection data if available in order to avoid mixing them and the potential of hybridisation.

Member species have also been organised into a series of species lineages, complexes and groups by authors in order to better separate them. Such lists have been augmented by fish that have appeared in the aquarium trade and are in a state of near-constant flux

For many years G. affinis was thought to be the same species as the Eastern Mosquitofish, G. holbrooki, but has since been given distinct species status. They can be distinguished by several means. In G. holbrooki the leading ray of the males' gonopodium has a serrated edge, theusually has 7 rays and males also generally have a higher degree of dark spotting on the body than G. affinis males. Male G. affinis also lack the serrated leading ray of the gonopodium and this species usually has o…

Numerous ornamental forms of this species have been selectively-bred for the aquarium trade. It has also been assigned the ‘A’ number A234 under the DATZ system with possibly conspecific, related forms similarly numbered A103, A104, and A105 depending on locality.

Numerous ornamental forms of this species have been selectively line-bred for the aquarium trade, vernacular names for which include "sunset", "sunburst", "double red", "triple red", "gold", "white gold", "orange flash" and "albino". It has also been assigned the 'A' number A200 under the DATZ system with possibly conspecific, related forms similarly numbered A201, A202 and A203 depending on locality.

Th…

This is an exceptionally hardy and adaptable species. It's not an especially common fish in stores, but is quite widely available in hobbyist circles. The common name arises from the row of modified, paired scales that form a keel running from the base of theto the caudal fin….

The eye of Anableps species is split horizontally by a band of epithelial tissue. It has two corneas, two pupils, a single, egg-shaped lens and one retina that's also split into two sections. The lens is oval and asymmetric with the upper part flattened as in the human eye and the lower section curved as in most other fishes. The upper cornea is thicker and enriched with glycogen which possibly helps to protect it from drying and UV irradiation. Two horizontal flaps of the iris are thought …

The genus Acarichthys remains monotypic and was resdescribed by Kullander (1986) who characterised it by the following: lack of epibranchial lobe; comparatively few (12-14)rays; pelvic fins with relatively broad tips (branches of the first ray are equal in length or the inner is slightly longer); possession of a single supraneural plus 14-15 vertebrae (these characters taken as a combination); no caudal extensions to swim bladder; no caudal ribs.

Its current taxonomic position is based largel…

T. heteromorpha was first exported for aquaria in the early 1900s and has gone on to become one of the most familiar, enduring species in the hobby. It has suffered as a result of its popularity to a certain extent with the mass-produced fish we see today lacking much of the colour seen in wild specimens and even exhibiting morphological deformities in some cases.

Several selectively-bred ornamental strains have also…