I've raised multiple species of Geophagus and multiple groups of sveni and...
Agree: 1) You cannot sex sveni by appearance, certainly not at that size. Color is the same, females also develop long fins as they near maturity, and ime it isn't until a pair begins breeding that a female slows down growing while the male puts on more size for a while. It depends on the individual fish, but up to then a female might be among the largest in a group. So to breed them you'd need to get a group and let them pair off. At that size and if you're not interested in breeding, you might be able to keep fewer than 5, but this will depend on whether the individual sveni decide to get along with each other, which isn't a given. 2) They're a space hungry species, they don't always, but males are capable of reaching 10 inches, sometimes more, and at 5,6 inches they're getting to just the size when they're prone to start fussing with each other-- although to what extent depends on the usual factors of male/female mix, individual temperament, tank mates, and tank size. Imo, with 5,6 inch sveni you'd already be on the verge of being overstocked and I'd expect needing to either move the oscar or pare down the sveni group before long. 3) No one has said it in this thread yet, but, yes, you often see people say geos are slow growing. I don't know what they're comparing them too, something like an oscar, maybe, but otherwise not at all in my experience. And it's more than water changes that affects growth, nutrition is also a factor, including ingredient quality and not overfeeding or overfeeding protein. Aquaculture studies on multiple species are consistent showing there's an optimal range for each, and growth is slower when going either under or over that range.
Disagree: Yes to good filtration, clean water, and plenty of oxygen, but they do not need a lot of current-- sveni are among the 'high bodied species that prefer slack water areas' (see the Geophagus habitat section of
this video at about the 37 second mark). While not a rapids loving fish, they can adjust to varying levels of current and are perfectly happy living in quieter conditions suited to angelfish or discus. In fact, I often keep them with Heros species and/or wild or F1 scalare angelfish.
Only partially agree: Small and juvenile geos do prefer to be in groups of their own species, and this way you see more of their social behavior, but it doesn't matter as much as they reach maturity. People have kept singles in a community and they seem to do fine, though it's not what I'd do. But a pair is perfectly content to themselves in a compatible community, sometimes more so, not having to compete or fuss with others for spawning territory. This wasn't much of a factor when I had pyrocephalus and I could have two breeding pairs, an extra female or two and some juvies in the same tank. But with my current sveni group I had to move the dominant pair to avoid a total ruckus each time they were ready to spawn, in part because they consistently wanted to take over most of the tank, which didn't sit well with the rest of the group.
...Interesting to me how rarely the 'prefer to be in groups' point is mentioned with fish such as Heros species, Pterophyllum (angelfish), or some of the other social species that travel in groups in the wild. How often does anyone say
don't get just one or two severums, they like to be in groups?
