The thing i was thinking of is a rival frog, _Xenopus laevis_. That has been a classic model organism for research since the 1930s, and so ideally you would use that. But it's tetraploid - four copies of each chromosome. So are other related species of frog which are similarly useful. But not _X. tropicalis_ - that is basically "the Xenopus you can do genetics with!".

Zebrafish are diploid (i think), but their genome underwent a duplication during evolution, so they have two copies of each gene on each chromosome (more or less), which makes them hard to do genetics on in the same way as being tetraploid does.