This species is one of a group of similar-looking striped congeners alongside D. anomalus, D. coxi, D. devario, D. malabaricus and D. xyrops, among others.
Its name has been applied to almost any striped Devario, and in most aquarium literature to the commercially bred 'giant danio'. Genetic and morphological data have identified that fish as D. malabaricus (see that profile).
McClelland's description is brief, and the drawing that accompanies it shows a fish with a deeply-forked caudal-fin, small dark spots in two or three rows near the back, and no other colour pattern (see images). Kullander et al. (2017) applied the name to the striped fish found in the area Griffith collected in, since no species known from there matches McClelland's description more closely.
Following Kullander et al. (2017) D. aequipinnatus can be told apart from all other Devario by its colour pattern of distinct, straight P+1, P and P-1 stripes, of which the P stripe is the widest and is equal in width from front to back or slightly tapering towards the tail. It also has 9½-10½ (exceptionally 11½) branched dorsal-fin rays and usually 12 scales around the caudal peduncle.
D. coxi, described in the same paper from near Cox's Bazar in Bangladesh, is very similar. It has 11½-12½ branched dorsal-fin rays, 14 scales around the caudal peduncle, and P and P-1 stripes that join towards the front of the body and contain light spots.
Perilampus ostreographus McClelland, 1839, described in the same work, was treated as a synonym of D. devario for many years and revalidated by Conway et al. (2009). Kullander et al. (2017) tentatively placed it in the synonymy of D. aequipinnatus, which the Catalog of Fishes follows. They also listed Danio assamensis Barman, 1984, known from only three specimens from the Brahmaputra in Assam, as a possible synonym.
In recent years it's become commonplace to refer to the stripes on the body and fins of danionins as follows:
- P stripe: or "pigment stripe" is the central, dark, lateral stripe on the body which extends into the caudal fin in some species. Stripes above it are numbered P+1, P+2, etc. and those beneath P-1, P-2, P-3.
- A stripe: the central stripe on the anal fin; the proximal stripe (above it) is A+1 and the distal stripe (beneath) A-1.
- D stripe: The submarginal dorsal fin stripe.
Following Fang (2003) Devario spp. are characterised by: possession of a P stripe extending onto the median caudal fin rays; a short maxillary barbel (absent in some species); absence of the A stripe (a less distinct, relatively wide stripe is present in some species e.g. D. acrostomus, D. annandalei, D. xyrops); a short, wide premaxillary process (cleft in the upper jaw) with a tiny apophysis (bony tubercle) touching the kinethmoid bone; infraorbital 5 not or slightly reduced.
The current genus name has only been in general use since 2003 prior to which members were considered to belong to the genus Danio.
Older, molecular, phylogenies tended to agree that the latter represented a monophyletic group consisting of two major clades; the 'Danio devario' group containing the larger, deeper-bodied species and the 'D. rerio' clade comprising the smaller, slimmer fish.
In 2003 Fang Fang conducted a more detailed study based on morphological characters which included members of other related genera, and the results suggested for the first time that Danio represented a polyphyletic grouping, i.e., not all members derived from a single common ancestor.
The genus name Devario was suggested for the larger species with Danio being applied only to the smaller fish, although Kottelat (2013) later restricted Danio to its type species, D. dangila, and placed most former members in the revalidated genera Brachydanio and Celestichthys. Kullander (2015), the Catalog of Fishes and FishBase do not follow that split and keep those species in Danio.
These results have largely been supported by subsequent phylogenetic analyses (e.g. Mayden et al., 2007), although Devario has still undergone a little reshuffling, particularly following Fang et al. (2009) and Kottelat (2013).
In the former study the two species previously comprising the genus Inlecypris were brought into synonymy with Devario and three species formerly included in Microrasbora were moved into the new genus Microdevario based on possession of shared synapomorphies with Devario. The existence of a monophyletic clade consisting of the genera Devario, Chela, Laubuca, Microdevario and Microrasbora was also hypothesised, a theory upheld in the more recent study by Tang et al. (2010). The genus Betadevario (Pramod et al., 2010) is also nested within this grouping and is sister to Devario and Microrasbora.
Kottelat (2013) revalidated the genus Inlecypris whilst noting that phylogenetic evidence suggests the existence of two genetic lineages within Devario. The first contains the species with prominent lateral stripes, which leaves the remaining members (D. apogon and D. chrysotaeniatus) of uncertain taxonomic placement. In addition, a number of the striped species share a colour pattern comprising a midlateral stripe on the posterior half of the body with a few bars in the anterior portion and golden patches between them. These may eventually be placed in a separate genus for which the name Parabarilius is available.
Thanks to Rahul Kumar.
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