The specimens of this species have a green or golden brown coloration, with brown tones, and the white color intensifies to the belly, four lines of blue, ranging from opérculos to the flowing fin, cross the sides longitudinally. The males have a thin and compressed body, with a very notorious genital papilla, and they are smaller than females, with predominantly golden coloring; females exhibit a distinctive genital papilla, their body shape is thicker, they have a bulging and rounded belly and their predominant coloring is olive green. Figure 2 shows images of Danio Rerio and its related species, generally known as danios.
Zebrafish lives in small banks ranging from five to twenty individuals; they are reproduced and disposed asynchronously, on the substratum they deposit their eggs, which are not cared for by the parents after spawning. Like other fish from monsoon regions, the rainy season marks the beginning of the breeding season, although females have been observed with mature ripeness during the drought period, which allows us to assume that reproduction is more correlated with the availability of food, which is intensified with the rains. Fertilization is external and the eggs, depending on the environmental conditions, release larvae that swim freely after four to seven days of being fertilized. Males are territorial over possible spawning sites and adopt tactics to persecute females. Of his life cycle there is only laboratory data, where they live up to five years.
Regarding their diet, these fish are generalist, that is, they consume a wide variety of crustaceans on the seabed, as well as worms and insect larvae, although they show a marked preference for Diptera larvae, so it has been proposed its use for mosquito control.
Taxonomic treatment and phylogenetic relationships: Zebrafish model
Table 2 presents the taxonomic treatment of zebrafish and species that belong to the genus, known in general as danios, a family that also belongs to very popular fish in the Aquarius, such as golden fish, koi and common carp.
Modern phylogenetic analysis does not consist in finding ancestors in the fossil record, nor in the reconstruction of hypothetical archetypes. Instead, it is the recognition of groups of organisms based on the morphological or molecular characteristics they share, assuming that evolution is dominated by linear offspring and certain events that branch it. As a result, phylogenetic relationships between organisms are generally represented as branched trees.
An evolutionary novelty, be it morphological or molecular, will remain in the descendants of the organisms from which they have originated. As a consequence, a group will include all descendants of a common predecessor – known as a natural group, a monophyletic group or a clade – that can be recognized because all its members have one or more characteristics that have appeared first in this common ancestor. Organisms that are not descendants of this ancestor nor are members of that group lack the characteristics that delimit the natural group and are called synapomorphies or derived characters from the group. Natural groups do not overlap, but they are always hierarchically associated side by side. The analysis of evolutionary relationships (Figure 3) performed with homologous DNA sequences shows that Danio species have a monophyletic origin, that is, they form a natural group with a common predecessor and that Devario is their brother group.
Since genus Danio species are closely related to Danio Rerio, from the point of view of evolutionary biology they can be treated as natural mutants, which allows very well that this set of species can be used in studies of comparative biology and evolutionary biology.