So you have a Genus name. It's an umbrella name. You can have TFFis as a genus. Within is in it, we can have the species. TFFis magnummanensis could be one, with TFFis essjayensis as another. T. essjayensis could have dorsal filaments, and magnumanensis could have purple spots and green eyes. They would never meet in nature. They'd have different accents and social behaviour. TFFis Garyeis would be a fantastically handsome species known to dig itself into holes with stretched examples.
They would be related, but usually isolated by natural barriers for long enough periods that they were different. They wouldn't interbreed, but all their young would look like the parents.
If the species had only recently diverged (a few thousand years) maybe hybrids would be possible, but they might not be likely. They could breed mules, which would not have a scientific name because they were one off creatures that wouldn't have a future. And it would be generally safe to keep them with Otherforumensis uncooloserae.
Some young species cross easily, like Poecilia livebearers, or Melanotaenia rainbows, which compared to most fish, are new arrivals. Ancient fish, like killies, which have been around 150 million years or so, are less likely to hybridize. But life is a shrubbery - and new species are the tips of the recent growth. They're much more likely to cross, because they aren't set in their genetic paths yet.
In my Gabon adventure, we found several species that were "new", ie, they had never been studied by scientists. We gave samples to the Ichthyologists working on the groups, and for now, gave them temporary names based on where they were caught and who caught them. So if we caught a fish we didn't recognize after checking the serious sources, but we could identify the Genus, they were named as, for example TFFis sp. Paris.
The "sp." stands for species unknown, and Paris says where we caught it. We caught a tiny barb that really looked like Enteromius jae. But there, we have a complicated group of possibly different species that look almost the same. If I shared my jae with a breeder who had a genetically different but really similar one (the DNA is important with similar looking species), that breeder would get mules and I would have wrecked his/her project. So they are labelled Enteromius cf. jae, meaning really similar to, but uncertain.
Once we get organized, it will be possible to use a code, in our case GCDELMM 23 and a number. That will allow each discovery to be looked up, with its GPS coordinates, water parameters, temperature, etc. G is for Gabon, 23 is the year and the other letters are the first initial of the family names of the fishers, to identify which expedition.
