This species, here presented in the genus Rivulus, is originally described in the genus Melanorivulus. It is herein considered to be a subgenus in the monophyletic genus Rivulus. See: <Melanorivulus introduction>

See part of the original paper with a key to the members in the species greoup.

A new species of Melanorivulus, belonging to the Melanorivulus zygonectes species group, is described from the lower Rio Tapajós basin, Pará state, Brazil. Melanorivulus aithogrammus, new species, was recorded from a small tributary in the left bank of Rio Tapajós, Amazon basin. It differs from the other species of the Melanorivulus zygonectes species group by its color pattern in males, presenting sides of body light gray, with irregular oblique red bars, some in the shape of an inverted "Y", caudal fin hyaline with 5-6 brownish-red vertical bars, and pointed anal fin. A key to the species belonging to the Melanorivulus zygonectes species group is presented.

See down her this great KEY to this species group.

Key to the species of the Melanorivulus zygonectes species group (adapted from Costa 2016 and Nielsen 2017), including M. aithogrammus.

1 - Body sides, in males, with narrow, continuous oblique red bars forming chevron-like marks; caudal fin, in females, with distinctive white area above caudal spot, posteriorly extending as series of small white spots; usually 5 or 6 pelvic-fin rays, 7th ray rudimentary ............................................................... 2

Body sides, in males, with oblique rows of red dots, sometimes in contact to short oblique bars on dorsal portion of flank and caudal pe- duncle area, caudal fin in females without dis- tinctive white area above caudal spot, always 7 pelvic fin rays........................................................ 3

2 - Body sides, in males, with red marks along its entire extension; middle portion of caudal fin, in females, with dark grey to black bars; 28- 31 caudal-fin rays ............................... Melanorivulus kayabi

Body sides, in males, with narrow and irregu- lar red marks; caudal fin hyaline with 5-6 brownish-red vertical line, in females, body with dark grey to black irregular marks; 23-24 caudal-fin rays, dorsal-fin rays 6-7 ................................ ...............Melanorivulus aithogrammus

Body sides, in males, with rudimentary red marks; middle portion of caudal fin, in fe- males, with dark grey to black irregular marks; 31-33 caudal-fin rays ......................... Melanorivulus modestus

Body sides, in males, light brownish gray, with narrow 10-13 oblique red bars forming an “X” pattern below lateral midline; in females, caudal fin with bright yellow background, more intense in the upper and lower regions and paler at the central region, with 3 thick black vertical bars, distal margin with a thick black band ............................. Melanorivulus britzkei

Body sides, in males, metallic green, with 11- 12 oblique brown bars, bars with one or two narrow red oblique lines, when two narrow red oblique lines present, parallel and connected by 1-3 narrow red lines; in females, presence of a black spot at upper portion of caudal fin........................... Melanorivulus canesi

3 - Red marks interrupted along body midline; in males, lower jaw without red pigmentation.......................................... 4

Red marks not interrupted along body mid- line; in males, tip of lower jaw with red pigmentation.................................... 5

4 - Caudal fin, in males, pale blue, with broad red bars, often connected to reticulate pat- tern; anal fin, in males, with intense bright blue color on basal portion, contrasting with red marks; middle portion of caudal fin in fe- males not reticulate, frontal squamation F- patterned......................Melanorivulus ubroreticulatus

Caudal fin, in males, orange, without bars; anal fin, in males, never with intense bright blue color on basal portion; in females, mid- dle portion of caudal fin reticulated, frontal squamation E-patterned............................Melanorivulus petrisecundi

In males, all fins orange, with small and few oblique red spots only on the posterior por- tion of body; small, few reddish-brown spots at caudal fin, red spots not arranged as chevrons, black pigmentation absent on the head, females with 3-4 reddish-brown bars at the caudal-fin...Melanorivulus imperatrizensis

5 - Caudal fin, in males, with dense orangish pink pigmentation along the whole fin ..................................................6

Caudal fin, in males never with dense orangish pink pigmentation along the whole fin............................................................ 8

6 - Body sides, in females, with red dots well sep- arated by interspace; caudal fin, in females, reticulated, at least on its dorsal and posterior portions, and with a reddish grey basal spot; body depth 22.1-24.9% SL in females; cau- dal-fin length 23.6-25.2% SL in females; cau- dal-fin length, in males, 32.3-37.7% SL; 10- 11+1 neuromasts around orbit ................................. Melanorivulus spixi

Body sides, in females, with red dots united, forming oblique bars; caudal fin, in females, never reticulated and with black basal spot, without red pigmentation; body depth 20.0- 22.2% SL in males, 20.2-22.3% SL in females; caudal-fin length, in males, 37.3-42.3% SL; 12-14+1 neuromasts around orbit ............................................................. 7

7 - Distal margin of anal fin, in males, without black marks; caudal fin, in males without red bars; pre-dorsal length, in males, 73.9-76.2% SL........................ .............Melanorivulus salmonicaudus

Distal margin of anal fin, in males, with a nar row black margin; caudal fin, in males, with narrow red bars on basal portion; pre-dorsal length, in males, 76.9-80.5% SL......................................... ....................Melanorivulus megaroni

8 - Body sides, in males, with minute red dots, diameter of larger dots about as wide as pupil diameter or slightly less.............................. 9 Body sides, in males, with small red spots, diameter of larger spots about half pupil diameter or slightly more ...................................... 10

9 - Caudal fin, in males, light bluish with dark grey bars; caudal fin, in females, with round basal spot, its diameter equal to or greater than eye diameter............ . Melanorivulus karaja

Caudal fin, in males, hyaline with small dark pink spots; caudal fin, in females, with basal spot subtriangular, smaller than eye....... Melanorivulus zygonectes

10 - Body sides, in males, with red spots irregular- ly arranged ......................... 11

Body sides, in males, with red spots arranged forming oblique rows.................................................... 12

11 - Caudal fin, in males, with transverse rows of small red spots over whole fin except marginal areas; caudal fin, in females, with 3-5 dark grey to black bars; pelvic fin, in males, not surpassing urogenital papilla posteriorly; pelvic fin, in males reaching between base of 1st and 3rd anal-fin ray, its length 13.1- 15.1% SL............ Melanorivulus parnaibensis

Caudal fin, in males, with transverse rows of small spots over whole fin, sometimes minute red dots restricted to basal portion of fin; cau- dal fin, in females, with 5-8 dark grey to black bars at base of 1st and 3rd anal-fin rays; pelvic fin, in males, not surpassing urogenital papilla posteriorly, its length 10.4-13.0%SL..... Melanorivulus wallacei

12 - Caudal fin, in males, subtruncate, with faint reddish orange pigmentation on ventral mar- gin, and dark red bars on middle portion; in males, dark red bars extending over most dor- sal fin ............................. Melanorivulus javahe

Caudal fin, in males, oval, with distinctive reddish orange to intense red pigmentation on ventral margin, and without red marks on middle portion; in males, dark red bars restricted to distal portion of dorsal fin............................. 13

13 - In males, distal margin of dorsal and anal fin, dorsal margin of caudal fin, and anterior margin of pelvic fin without orangish red pigmentation; in males, reddish orange stripe on ventral margin of caudal fin abruptly narrowing posteriorly, not reaching posterior portion of fin.......... Melanorivulus crixas

In males, distal margin of dorsal and anal fin, dorsal and ventral margins of caudal fin, and anterior margin of pelvic fin with orangish red stripe, caudal fin stripes not narrowing posteriorly, reaching posterior portion of fin .............Melanorivulus rubromarginatus

No breeding data yet.

Remarks :

Max. size 0.0 cm.
Dorsal 00.0,
Anal 00.0,
D/A 0.0,
LL scale count (average) 00.0
Pre- dorsal length to % SL – 00.0 %
Depth to % SL – 00.0 %