“Buenos Aires Tetra”
This is the first tetra that I spawned successfully. I bought them on impulse at a club auction and it took a lot of tries before I got fry. It was a log time ago, so no photos.
The main thing I remember about this species is that they loved to eat duckweed and Wolfia. At the time my planted tank was producing huge quantities of Wolfia and I would scoop out a netfull every day or so to feed to these tetras; they grew up largely on a vegetable diet and these days I’m tempted to get another school for duckweed-removal purposes.
Once the fish were full-sized (pretty big for a tetra) I started isolating pairs in a 5-gallon tank with an egg-crate grid. They spawned like clockwork, almost always the day after I isolated them, but 100% of the eggs turned white and none of them hatched. This was using Minneapolis water, so already quite soft (tds around 130ppm).
After quite a bit of despair and advice-seeking I finally got around to buying a carboy of r/o water from an aquarium shop and refilled the spawning tank with that. The next spawn was a full-blown success with large, sturdy fry — soon I had more of these tetras than I knew what to do with.
I’ve never looked back — basically all the other tetras I’ve raised were spawned in pure or 50% r/o water. It is /probably/ calcium that prevents eggs from getting fertilized but I haven’t done a full side-by-side test to see if it’s specifically about calcium or just about osmotic pressure.