Cory cats are addicting

[GaryE]

I once picked up a good piece of info talking with a pleco seeker who had just returned from Brazil. He had gone there with very little interest in the Cory group, but said he was standing in a shallow brook as one of the spotted Corys migrated to deeper waters. He figured the brook was drying up and they were leaving it, as it was dry season. He was delighted with what he described as thousands of Corys snuffling past his ankles.
He said they went to the main river and fished for Loracarids, and when he returned a couple of hours later before they got into the boat, the Corys were still coming. He was astonished at the numbers. He said there were nowhere near as many of them as there were cardinals in other areas, but he was impressed.
I didn't have a lot of Cory experience back then, and tended to keep them in 2s or 3s. That throwaway story made me start seeking groups, and since then I have enjoyed them infinitely more. I think they've also enjoyed my tanks a lot more.
They only congregate like that to move, and live in smaller groups. But small is a very relative term.

 

[AdoraBelle Dearheart]

He was delighted with what he described as thousands of Corys snuffling past his ankles.

I love that description. They are a snuffling kind of fish!

 

[10 Tanks]

Serious scientific studies have shown many fish species to recognize individuals within their species. How do you think they maintain their rank in groups, and recognize their partners?

Some even recognize the person who feeds them. I have some shy fish that swim all over when they see me, but hide the moment a new person wants to see them.

You can't base theories on limited experience with only a few species of fish. Have you ever kept multiple groups of Corys?

I've noticed, with Cory group fish in large tanks over the years that when darkness comes, their sleeping groups are their own species. If you keep 10 of 3 species in a tank, you get 3 night groups, even if they rumble along together all day.

Technically, they should be in groups of hundreds, but we can't do that. In wild, underwater footage, they are often seen in little one species groups of 6 or 7 individuals, foraging within sight of the larger "herd". From that, I think they can go well in groups that size in the aquarium. It makes them a lot more fun to watch, as they are relaxed and kind of goofy. The number 10 is thrown around, but it's a random number. The more the merrier is the real rule.

If they aren't smart enough to recognize the danger of a rainbow shark/barb, they could lose an eye. That's a fish I'd never keep with Corys. As for plecos, they feed on completely different foods, and the Corys would probably just ignore them. They ignore my Ancistrus here, and plecos would be the same, til they grew.

So for what it's worth, I would try to get more of the same for the tank. Adding different species is tempting, but I tend to think of 6 Corys as one working unit of cats. The last group I bought, of Corydoras melini, was 10 fish. If you can only raise the group size by one or two, do it. You will see a change in how they behave, and a radical increase in how cute they are to watch.

Hello. Just passing along some things that I've noticed. That's all.

10

 

[sharkweek178]

Hello again. You know, I've heard that Corydoras need groups, but you know what? I really don't think fish have the capability of distinguishing the difference between themselves and other fish that prefer to hang out around the bottom area of the tank, like Plecos and Rainbow Sharks. They'll forage around the tank with other fish and believe that they're with others of their own kind.

10

They absolutely can tell. By sight and by pheromones and other senses. Why do you think some schooling fish have distinctive colors, lines and patterns? It's so that they can see each other to school with.

 

[Rhysp87]

The one thing that keeps coming up is providing them with sand, and the more I read the more I feel guilty about only having gravel (it’s smooth and has caused no injuries but I know that’s not the point). Anyone got any suggestions about ways to introduce a small amount of sand into a tank without it getting mixed in with the gravel? I was thinking perhaps a Tupperware lid sunk into the gravel and filled with sand. Not sure how good that would look but would possibly make it easier to clean?

 

[Naughts]

The Tupperware lid would help keep the substrates separated. I remember @Colin_T suggests gluing substrates to the plastic to disguise it.
But you don’t need to ‘clean’ sand, you just swirl the syphon above the sand to lift up any debris on the surface. Its size means that it compacts enough so that debris doesn’t fall into it.
Which brings us onto bacteria in the substrate. Barbel erosion in cories is rarely caused by cuts from sharp gravel, it is caused by infections. The gravel allows debris to fall below the surface and then harbours bacteria. The cories continual sifting brings them into contact with the bacteria causing illnesses. Sometimes they also get infection on their bellies because they are on dirty substrate.
So, if you do keep some of the gravel, thoroughly clean it each time you do maintenance.

 

[10 Tanks]

They absolutely can tell. By sight and by pheromones and other senses. Why do you think some schooling fish have distinctive colors, lines and patterns? It's so that they can see each other to school with.

Interesting. That hasn't been my experience. My schooling fish will school for a couple of days, but once they feel secure in their tank, they completely stop schooling. Just another observation.

10

 

[GaryE]

@10 Tanks In a tank, they figure out they don't need to shoal, and the shoal breaks up. It takes a lot energy to maintain, and if they see nothing scary, they relax and just forage. But if you watch, they keep an eye on each other if the group is large enough. If they're frightened, they're right back into the convoy.
If a group shrinks over time and you don't replace the fish that have timed out, they often understand the tank and stay the same. But a lone individual in a new tank won't forage til it's desperate, and always looks like it has an eye out for whatever ate all its companions. It isn't wired to be alone, and it's main defence is the shoal.

It's like the old trick - set up hiding places, and a lot of fish won't hide. Put them in a bare tank, and they're behind the filter all day.

If you notice the tetras in a underwater video from the Amazon, they are in groups we can't consider in our small tanks. Even small shoals can be hundreds of fish working together. And they tend to be one species, like schools. They know.

As well, your fish never schooled. We tend not to keep schooling fish because they need huge space to have the numbers they need. A shoal is what we see - a temporary defensive group. Schooling fish stay schooling, and if we could have schools of fish, we'd be happy. That's a holy grail for tank keepers, because we've all seen the beautiful videos.

 

[10 Tanks]

Hello. Just some observations, not based on anything very scientific. I'm just watching the activity in my tanks on a daily basis. Sorry, but this is way too much information to read. I don't have a lot of help with all the big words. So, anyway, I'll keep my observations to a minimum here and just add a few observations and information to my journal. Thanks!

10

 

[sharkweek178]

Interesting. That hasn't been my experience. My schooling fish will school for a couple of days, but once they feel secure in their tank, they completely stop schooling. Just another observation.

10

Yes, but those visuals on the fish give them the ability to school when they feel like they need to. Take rummy nose tetras. One of the things that gives them the ability to school as tightly as they do is their distinctive red faces and striped tails that are a visual cue to the other fish.