11/06/2026
🦎🌈🐠 LIZARD TETRAS - SPOT THE DIFFERENCE 🐠🌈🦎
Let’s play a game of Spot the Difference 😂.
There’s a lot to take in…so take a deep breath…here goes!
A while ago we received a shipment from South America containing what we thought were Rainbow Lizard Tetra (Iguanodectes adujai). Well, in the coming days I became convinced we had more than one species in the mix. It turned out that after plenty of research and checking (they weren’t as developed or colourful as they are now, so wasn’t easy), we infact had two species, much to my delight. Joining the Red-lines were some Red-line Lizard Tetras (Iguanodectes geisleri)!
As you can see these are both rather beautiful and endearing Tetras. Not often seen and not as popular as the staple Neon Tetras, these active and peaceable Characins are certainly a worthy addition to any suitable larger community tank. They add a splash of iridescence and character to the tank, and any Tetra enthusiast must surely consider these much underrated fish for their home aquaria. Who knows, you may even crack the breeding of them as there appears to be no known records. Anyway…on to the lowdown.
FIRSTLY…THE SIMILARITIES:
These rather underestimated yet colourful and active Tetras are both endemic to parts of Brazil and Venezuela. They were both first described in 1970.
Firstly, the Rainbow Lizard Tetra’s (I. adujai) type locality is the Rio Adujá (for which it is named) and the Rio Itú which are both tributaries of the Rio Negro in Brazil. More broadly, the areas they are found in are the Rio Negro in the Brazilian Amazon Basin and the Upper Rio Orinoco in Venezuela.
Secondly, the type locality for the Red-line Lizard Tetra (I. geisleri) is the Rio Jufaris (again, a tributary of the Rio Negro), Igarapé de Paricá in Brazil. More broadly, these are found in the Rio Madeira and Negro in the Brazilian Amazon Basin and again in the Upper Rio Orinoco in Venezuela. So it is perhaps easy to see how these would have been included as bycatch with the Rainbows.
The first part of the genus name ‘Iguanodectes’ comes from an ancestral predecessor of the historically extinct Taino language. Iguano is derived from the Taino word ‘Iwana’ meaning ‘Lizard’. The second part comes from the Ancient Greek word ‘Déktés’ meaning ‘Biter’. Don’t let that part put you off though…they are peaceful! In regards to the species names, adujai is named after the Rio Adujá from where that species is found, and geisleri was named for the German aquarist Dr Rolf Geisler (1925-2012).
Their native habitats are believed to be identical. They are found in predominantly blackwater river areas, although their body shape does suggest they are found in faster flowing stretches. The substrate is generally humic, producing plenty of tannins from the decaying leaf litter, with the water column punctuated with plenty of branches and roots.
They are also known to inhabit a type of lowland stream known as a Morichal, a transparent clearwater habitat found in savannah areas of South America, usually with sandy beds and thick dense vegetation within which the fish can hide.
When accommodating these Lizard Tetras, generally bear in mind the advice above when decorating your aquaria, which should be a minimum of around 120cm or approximately 200-250l minimum.
They both have a temperature range of 20-26c and prefer a PH range of around 5.0-7.0, making them fairly undemanding and easy to maintain for most aquarists in those respects. Both are considered omnivorous, and will readily accept most foods such as Bloodworm and other insectivorous offerings in addition to crustaceans including Brineshrimp. Prepared dried foods including flake and small pellets are more than readily accepted, and even filament algae too. It will surprise you know that in their wild habitats, they are even known to consume small fallen fruits!
Both are pretty peaceful (perhaps aside from long-finned fish) and are best kept in groups. Ideal tankmates include, for example, small Tetras, Rasboras, Barbs, Rainbowfish, Dwarf Cichlids, peaceful larger Cichlids, Corys and Suckermouth Catfish. As these Lizard Tetras are active fish, for those tankmates destined to occupy the mid to upper water column, it may be wise to choose similarly active fish too for the most part.
THE DIFFERENCES:
There are believed to be only eight species of Lizard Tetra in this genus. Some are different, but at least three are similar. Luckily we are only dealing with two. On the surface they are almost identical, especially when they haven’t settled in and shown their full colours and markings.
To confuse things, both are traded sometimes as Red-line Lizard Tetras, but only one species bears this name. The most obvious and key difference between these two is the position and size of the a**l or pelvic fin. With the Rainbows, although hard to see in the photo unless you zoom in (I tried my best), the pelvic fin is much longer in terms of the fin ray count, with the anterior or leading edge being directly below the anterior edge of the dorsal fin. If you zoom in you can just about make out the position of the leading edge of the pelvic fin. With the Red-line though, the pelvic fin is set back in a posterior position to the dorsal fin and is therefor shorter.
Rainbows have more of a greenish base colour than the Red-lines which are more silvery. Rainbows lack the Red-line’s black lateral stripe that is below the red lateral stripe (which is more orange on the Rainbows).
Rainbows have quite a luminescent orange top lip which in the the Red-line’s is more ruby red and not that prominent, if at all. Both possess a black mark on the caudal fin emanating from the caudal peduncle. However, there is a subtle difference in that with the Rainbow’s it is positioned just into the lower half, whereas the Red-line’s marking is roughly central. In both, these markings are variable in shape and size.
Rainbows do get some faint colouration on the dorsal fin (perhaps males?) but the Red-line males develop some intense colouration to their dorsal, ventral, a**l and caudal fins. In females this is absent. Finally, Rainbows attain a length of 6.2cm and appear more streamlined, whereas the Red-lines max out at 5.5cm
And breathe! 😂
So…you got it nailed? 😂 When you decide which species you’d like to try, then please call us up for prices or anything else on 01420-489560. Better still, pay us a visit as these fish are really best seen in the flesh as the piccies really don’t do them justice! You really won’t be disappointed. Be bold and try something a bit different!
See you soon I hope!
🦎🐠🦎🐠🦎
Lic17173
