Ime, all juruense will eventually get nice colors as they get larger. In order to really understand the coloration of these fish, we must understand what these fish are and how their color expression functions.
The most important part going into this is to realize that a Brachyplatystoma juruense is a light colored fish with a dark-colored-pattern masking gene. This is the opposite of Brachyplatystoma tigrinum, which is a dark colored fish with a light-colored-pattern masking gene.
In other words, jurs are a white zebra with black stripes, tigs are a black zebra with white stripes.
This is important to how the fish express their patterns. When a teleost changes colors-- something they can all do to some degree-- they can generally only change the base color, not the markings that are expressed through a masking gene. In tigs, this means that regardless of the conditions in which the fish is being kept, you're going to have a fish with brilliant white stripes over a base coloration that is anything from a vivid black background color to a medium brown background color.
With a juruense however, this works a little differently. Jurs are a light colored fish with dark markings. This means that you're going to have rich, thick, nearly black markings on a fish
that has thin stripes of the lighter base color. Again, a teleost's base color is what it can change; and for jurs, the lighter base color can change from vivid white or yellow to being nearly as dark as the masking pattern.
In both tigs and jurs, this change happens because the part that changes colors is the base color, which is black in a tig and white in a jur.
This pattern is incredibly variable in both, but the pattern can be very roughly divided into three main categories with juruense:
1- Vertical: dark with many thin light colored up and down stripes
2- Diagonal: dark with thin light stripes that typically slant toward the back of the fish up from the belly
3- Mosaic: dark colored with a hodge podge of random light colored markings
Typically I see people try to say diagonals and mosaics are the flash zebras. I take this to be because these patterns are less common in the hobby, so therefore MFKers feel that they must be more valuable somehow.
In reality however, as they grow to maturity, all juruense will fade. The degree to which one fades is as variable as everything else with this fish's appearance, but it will fade. The dark masking pattern will break up as the fish grows, showing more and more of the brighter colors underneath. As they grow, all juruense will eventually become mosaics to some degree. There's a reason the finest examples fishermen catch are always huge.
But, why do fish caught while fishing have such vivid coloration? Why do fish in tanks only occasionally show this? How can I replicate this in MY tank?
First, let's address why jurs caught fishing look so nice. This comes back to the light colored fish with dark markings thing. All teleosts caught fishing "bleach" due to stress. I'm not sure why, but I've caught enough fish that I've thrown into a tank later to have observed this phenomenon take place. A prime example is how a blue catfish (Ictalurus furcatus) is a very light grey when you pull it out of the water on your line, but acclimated in a tank they're a deep, vivid cobalt blue. The stunner juruense we see with fishermen are in the stressed, "light grey" phase. The best example of this for a jur is that one George from Shark Aquarium caught in Brazil. It looked amazing on the hook, but comfy in a tank, it was always far darker and less showy.
Other factors in play are that jurs don't seem to like bright light in their tanks or in the wild. I've noticed a preponderance of fish caught from tannic or turbid waters often display lighter colors to a more advanced degree than do those fish caught from relatively clear waters. Indeed, in my own tanks as I've actively worked to test this hypothesis in the past. I have observed that jurs in dark or tannic tanks tend to display a brighter, more vivid base coloration. Inversely, a calm juruense seems to display the same colors as a highly stressed one on a fishing line. All the nice pics I have taken in the past of my jurs that displayed nice vivid yellow stripes were taken when the fish was relaxed and the room was dark. Then, when I turned the lights back on, after a few moments, the fish would darken again.
The only factor I've not yet tested is truly soft, acidic water. I don't know yet if this can precipitate the desired coloration or not, but I intend to test it in conjunction with the other factors listed above once the 550 is running (and I can find a jur or two).
I am with
C
Chicxulub
that all juruense probably become "flash" past 1.5'-2'.
So few people grow them out to an adult size and few of those who do it also report it, that we seem unsure of the "regular" juruense (what a shame). I don't recall a single thread where a small "flash" would have been shown to grow into an adulthood and what such result would be.
I have a 550 gallon tank and a ro/di system ready to go in my new house for the express purpose of addressing this.
And I agree, the lack of credit we give to small jurs is criminal. The pattern takes years to develop, it doesn't come out of the egg that way.
I bought what was labeled as and what I thought was a "flash" a few years ago but I suspected that it was just a good looking jur.
That's all a flash is, a good looking jur. A few years (ok maybe more than a few) ago we had a thread where we debated this ad nauseum. As it turned out, there was a huge debate where person A would share fish A as an example of a "flash zebra", then person B would share fish B and say this THEIR fish B was what constituted a FZ, and that fish A was a regular jur. Person A would then counter and say that fish B was the regular jur.
And so on and so forth until the point was effectively proven that a FZ was just a pretty jur, and beauty is in the eye of the beholder.
*Edited for clarity and for copious fat-fingers-on-a-phone induced typos
