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FAQs on the Penguin Tetras, Genus Thayeria

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False Penguin Tetra Aggression      4/7/17
Hi Crew! I hope this message finds you well.
<Does indeed, thanks.>
I have a school of false penguin tetras that are causing me a bit of grief. I've probably emailed about them before - I found them to be far too aggressive/active to be kept in the tank I originally had them in, so they have now got a 4 foot long, planted tank of their own.
<Penguin Tetras are pretty good, but they do have a vague reputation for being nippy. I think this holds for many South American tetras
, even though it's barbs that people most often think of as fin-nippers.>
There were Otocinclus in the tank too but after seeing the tetras harass one to death the surviving Otos have been moved to safety and I have not trusted the tetras with any other tankmates since - I would have liked a mid-to-bottom level fish or group of fish but right now I don't trust the tetras not to murder them straight away.
<Odd. This species is generally considered a good community species, at least, when kept away from slow-moving or long-finned fish like gouramis, guppies or angels. I'd not hesitate combining with loaches for example, or active barbs, both of which should have much the same personality. Night-active catfish should be fine too, such as Ancistrus or Peckoltia.>
I have bought several waves of fish trying to get a correctly sized school and eventually got 15 tetras. The newest ones were quite small, I was worried the bigger older ones would get violent as they have done previously with smaller fish, but initially this wasn't a problem and things were fairly calm. I even saw some apparent spawning behaviour when the new guys came out of quarantine to the display tank. As they grew one of them proved to be a bit of a runt, stunted in body length compared to the others. I didn't see the aggression start up but I believe this one might have been the first to be bullied to death as I found him all chewed up at the bottom of the tank after no previous signs of illness.
<This sort of 'mean' behaviour is quite common in schooling fish. Bear in mind a school of fish operates in a Mexican standoff sort of way. On the one hand the fish are competing for mates and food, but on the other need the security offered by schooling. There's a tension built into the system, unlike territorial fish (such as cichlids) that ignore rivals once rivals leave their territory. So what happens is that weaker fish in the group can't balance the aggression they give out with the aggression direct towards them, and such fish become stressed, sickly, or as you've seen here, simply badgered to death.>
I had another that developed a lump on its side which came on suddenly, after a few days it seemed like a popped pimple and the fish seemed okay but before long, a day or two, the site seemed to have ruptured and the fish died. Not sure if that one was trauma from bullying but I am now on to a third fish, which has first had the bottom half of its tail chomped off, and was like that for quite a few weeks, and now the top half of its tail is gone too - these are fairly precisely sized chomps and look exactly like the damage that was done to the Oto that died. It seems to confirm to me that aggression is going on. The affected fish looks pretty bad and I had put it in an isolation box (a long plastic 'Betta barracks' style breeder box with all the dividers taken out to give more space, and placed internally in the tank so it could at least see its schoolmates) to try and give it some peace, but it managed to push the lid off and escape to rejoin the school.
Each of these fish that I have mentioned was the smallest fish in the tank at the time (and I think the Otos were targeted due to their elongated body with dark lateral line, mistaken for another tetra) so the only conclusion I can come to is they are targeting the smallest for the brunt of the pecking order/squabbling type behaviour.
I rarely see it happening because these tetras are at the point now that if they see me, they stop what they're doing and come to beg for food, or if I get too close they huddle together at the back - it makes it a little hard to observe their behaviour directly. I think I'm right though that bullying is the cause just going by how they behaved when I had them in a smaller tank with other tank mates, and how I witnessed them behave to the poor Otos, and that it is always the smallest that is affected, and it didn't really start until the new ones had grown closer to adult size.
<Are they the only schooling fish in the tank? Something that works well is to combine two schooling species; in this case, something big, confident, but basically peaceful. Such a group will blunder through the Penguin school, causing them to work together (i.e., school up nicely) rather than fight, even though the bigger species isn't actually a threat. In brackish water fishkeeping, mixing Scats (big but friendly) with Monos (smaller and more feisty) works really well, but without the Scats, Monos often become hierarchical and mean to each other. What would I choose here? Perhaps one of the bigger Danio species, Giant Danios or Queen Danios maybe, or a Rainbowfish species. One of the more active loaches could work too, a school of Yo-yo Loaches for example. Another tetra species could work nicely too, if you're going for a South American feel. Something robust though, rather than Neons. I'd be looking at Bleeding Heart Tetras, Diamond Tetras or Rosy Tetras.>
I've tried to read for myself about how to solve aggression issues but I keep coming across "school too small" or "tank too small" explanations; I've tried to address the first point (but maybe the school still isn't big enough?) and on the second point, they have 4 feet with a decent amount of swimming space as the plants are established but not yet overgrown. I'm really stuck for ideas on how to defuse the situation and I expect if I do nothing, the next smallest fish will be the next target.
<I do think at this point you have enough tetras, and you'd get better results adding something else, if for no other reason than the tank would become more interesting.>
I am not against the idea of buying more tetras to try again for a bigger sized school, I do worry that the bullying would continue - but it could be that I have, by chance, ended up with a bad/uneven mix of genders. The other idea I had, trying to think logically about fish psychology, is to give them something to think about external to the school to distract them - some kind of peaceful but imposing tankmate that they will want to keep an eye on and unify against, or perhaps a second school of some other kind of robust, active fish. I don't have access to too many kinds of fish here. I'm thinking definitely not angels, Gourami are out; both have long fins that would get chomped. I like barbs but I also like my plants, so maybe some kind of Rainbowfish? A second type of large active tetra? A few loaches to also eat my snails?
<See above.>
I'm not really sure what would work that would be both distracting to the tetras but not actually dangerous, and conversely would be able to handle any aggression from the tetras if they chose to try and start something and lastly would be suitable (not too big) for the tank. I've never kept Rainbowfish or loaches before. I had zebra Danios and penguin tetras together at one time and that really did not work, again too similar in shape and in habit and they clashed constantly. I suppose the last idea would be to add more plants but I have been doing that too, it hasn't really helped much since these guys hang around at the top level and not many of the plants reach that high.
I'm keeping the tank at around 25ÂșC, TDS is 150-170 ppm and KH around 3-4 degrees and I do weekly water changes, if this helps narrow down a suitable tankmate. Currently the flow around the tank is fairly gentle but directional, no airstones running but I could add some for a fish that needs higher oxygenation. The rear of the tank is rounded pea-gravel planted with stem plants and Vallisneria, there are driftwood pieces with java fern in the centre and the front area is fine sand with a few smooth rocks, low crypts and some sad looking Lilaeopsis that isn't getting enough light. Duckweed and a few scraps of hornwort at the surface. And lastly the tank is covered with glass lids, with only a couple of gaps where the canister filter hoses and heater cables go in.
<Sounds nice.>
I really love the way these fish move together and do want to keep the school rather than get rid of them for some less mean, more politely behaved fish. I definitely would like to try to stop fatalities for the smallest fish, so I would love to hear any ideas you might have.
<Hope this helps, Neale.>
Re: False Penguin Tetra Aggression       4/12/17

Thanks for your advice Neale! The injured fish didn't make it and I've already seen some more chasing behaviour from the larger tetras so the cycle begins again. So far no further signs of fin damage, though! I've done a lot of reading and thinking regarding the suggested fish and I think yoyo loaches are my favoured option. Almost all the fish I've kept so far are small so I have been interested in keeping something that gets a bit bigger, and they look like super fun fish with engaging behaviours. They also happen to be about the only loach that's available here apart from clowns and kuhli loaches so I'm glad they were among your suggestions. I've ordered 6 and I've worked out ways to arrange my loose driftwood into what I hope are attractive cave structures for loaches. I'm grabbing some extra plants too, it seems like most of the tetra squabbling at the moment revolves around the very centre of the tank so I am going to try floating some wisteria there temporarily to break it up a bit while waiting for the loaches to finish in quarantine.
Your help, as always, has been invaluable! I hope you have a joyful Easter.
<Glad to have offered some help, and thanks for the kind words. Males of some tetra species do hold temporary territories around plants, presumably in advance of scattering fertilised eggs, but in any event, your idea of creating more visual breaks between the more aggressive fish might well work. Good luck! Neale.>

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