Peaceful by nature, vulnerable by size
A rummy-nose tetra has no interest in troubling anything. It carries no weapons, defends no territory, and spends its day travelling with its school through open water, which makes it one of the easiest fish to combine with other peaceful species. Its problem is the opposite one: at around two inches, slim-bodied and slow to scatter, it fits neatly into the mouth of a larger fish and cannot outswim a determined fin-nipper for long. So the question is never whether the rummy-nose behaves around other pets, because it does, but whether everything sharing its world has been chosen and housed so that nothing can treat the school as food or as a toy.
Tankmates that share a rummy-nose tank safely
Build the community around similar size, similar temperament, and similar warm water. Other small tetras, rasboras, peaceful dwarf cichlids that stay near the bottom, small catfish that work the substrate, and calm top-dwellers all leave a rummy-nose school free to use the middle layer it prefers. Keep the school itself at six or more, because a bigger group is a bolder group and spreads any attention from a boisterous tankmate across many fish. Avoid the classic mismatches: large angelfish that grow big enough to eat slim tetras, aggressive barbs that shred fins in passing, and any sizable cichlid that hunts at night when the school rests. Also mind the water itself, since a companion species wanting cool, fast flow will quietly stress a fish that expects warm, gentle conditions even if it never touches it.
Cats, dogs, and the world outside the glass
For the household pets outside the aquarium, the rummy-nose is only ever at risk through access. A cat that can reach open water will fish, and a cat that cannot reach it may still spend happy hours watching, which is harmless enrichment for the cat as long as the tank cannot be rocked or the lid lifted. Fit a solid, well-seated lid, site the tank on a stand rated for its filled weight, and keep the cat's favourite launch furniture from sitting level with the top. A school that stops showing its red colour in a pet-heavy room is often reacting to vibration and looming shadows, so a slightly quieter position can transform its behaviour.
Introducing new animals on either side of the glass
Add new fish the way you would want strangers added to a settled household: quarantine or at least close observation where possible, lights low on the first evening, and feeding watched carefully for the first week so the shy school is not outcompeted at the surface. When a new cat or dog joins the home, let it discover the tank under supervision, reward calm watching, and interrupt any pawing at the glass from the first day rather than the tenth, because habits around the aquarium set quickly. Watch the school itself as your referee: bright faces and a tight, travelling group mean the household mix is working, while pale, scattered fish hiding in the plants mean something in their world feels like a threat.
The bottom line for a multi-pet home
Nothing about keeping rummy-nose tetras rules out a house that already has a cat asleep on the sofa, a dog under the table, and other fish in the same tank, as long as each relationship is managed by separation, lids, and sensible stocking rather than by hope. Choose companions that cannot eat them, keep land pets physically off the aquarium, and let the school's colour tell you whether your arrangements are working. Should the whole setup one day pass to another keeper, KinsLe Transferrable Profiles record which tankmates this school lived with peacefully, alongside its routine and history, so the new home can rebuild a mix that already worked.