I don't believe on the cross breeding for several reasons.
- As far as I know, nobody is breeding Semaprochilodus. All are wild caught. No hybrids from that.
- In their natural habitats (as a genus, quite widely distributed, from the Guyanas to southern Brazil, west to Colombia, including several countries), these fish exercise massive migrations related to reproduction, which are likely quite species-specific. This makes frequent hybridization in the wild less likely.
- At this time there are 6 (six) known species in the genus Semaprochilodus: alphabetically, brama, insignis, kneri, laticeps, taeniurus and varii. Some are genetically more closer to each other than others, but at this time all are consider valid.
- While three of these taxa are supposed to be relatively common in the hobby, the others are only rarely (if ever) seen.
- Recognizing the various species is difficult, as they are very similar, particularly among immature specimens (read, not full developed, which is generally when they are exported). And then, there is individual variation, probably gender differences and others. Further, aquarium conditions may further affect how one individual fish looks like. Large ontogenic changes in appearance (during an individual fish lifetime) are well known as well.
- Altogether, it is hard to know what species one has, or which one is being offered at a LFS or online.
Below is a single fish at several times in its life. He/she is now somewhere in the 9-10 inch range; it started at about 2 inches. Note how its colors have changed, on body color pattern, fin color patterns, and individual fin colors.