I find it extremely useful to see "first hand" (in a sense) the habitat of a fish species. We can learn a great deal about the needs of a fish solely from the habitat/environment.
The cardinal, Paracheirodon axelrodi
, occurs in two known forms [see our profile for a description with photos] and that depicted in this video [filmed in Venezuela] is obviously the so-called "Colombian" form which occurs in the Orinoco basin and elsewhere in Colombia and Venezuela. The Brazilian form is endemic to the Rio Negro and Peruvian Amazon basins.
There was an article in TFH a few years back that included photographs taken by a professional diver. Some interesting facts about the habitat frequented by this species can be found therein. I'd have to dig through my research to track down the issue.
Back in August 1987, there appeared an English translation published in TFH of an article by Rolf Geisler and Sergio Annibal entitled Ecology of the Cardinal Tetra, Paracheirodon axelrodi (Pisces, Characoidea), in the River Basin of the Rio Negro, Brazil, as well as Breeding-related Factors
. Considerable test data on the water chemistry was included, along with morphology of the biotopes with seasonal differences and fish migrations. One of the most important facts to emerge from this article was the detrimental effect of hard water on the physiology of soft water fish.
Thanks indeed for posting the latest information and the video.