Bichir going wild

[SammyTargo]

Hello All.

For a little context, my friend has a tank that is African-themed aquarium, 75 gallon long. He keeps 12x Congos, 3x Kribs, and 4x Synadontis Petricola, and most importantly, 1x 5in male Senegal Bichir.

I have never kept a bichir before so I figured it would be best to ask here, which he asked me to do.

He turned on the light in the middle of the night (which he never does), to fix multiple anubias that fell off of the wood. When he did, he described that the congos got startled and swimmed around frantically. The bichir snuck up on one of the smaller congo females, and grabbed hold of it while swimming around the tank as the congo struggled in its mouth. This happened for about 3 seconds before he intervened and swooshed the bichir with a had made wave; promptly releasing the tetra which swam at max speed all the way to the other side of the tank to rejoin the school.

This has never happened in his tank before, and the bichir is constantly well fed, and sometimes even has visible lumps in his stomach from carnivore pellets. This hasn't happened before, proven as the bite marks on the tetra are very visible, and my friend has never seen anything like it in the past. The bichir is almost never predatory towards the other fish, except for one incident of fin nipping after a tetra went directly in its face which is common behaviour.

What should he do, and will this behaviour become more frequent in the future?

F.Y.I. he has an available 4 gallon to set up immediately with a filter, heater and all.

Oh- and as I am typing this up he is calling me and telling me how the bichir is being aggressive again and chasing the tetras around periodically (they are fast so he can't necessarily catch them at the moment).

 

[Magnum Man]

I call mine killer… he eats pellets, but has the desire to catch his food… I feed him 20 comet gold fish every once in a while ( about once a month ) and the last time, he had them all eaten in 2 hours… when he was 10 inches long, I had a large common pleco in the tank that was 8 inches long, and he ate the whole thing, a week or so later, I found a pellet, like owls do, with the bones, and that huge pleco skull rolled into a ball… I think owls cough them up, not sure which end the bichir passed the pellet, but I’d bet it won’t be long before all those pesky tetras are missing…

they don’t get huge, as far as predator fish go, but they death roll, like a crock… the local pet store always has these cute little ones that look like loaches… but they are destined to a solitary life…

mine out hunting

BTW… it only starts with the tetras, every fish you listed will be potential food, and nothing makes them grow faster than live caught food, so once it starts, it’ll be growing machine…

the one listed in the original post, can grow to 20 inches long… mine matures at about 14 inches, so is close to its mature size

 

[OMG_FL]

He most probably will do this again since he's naturally a predatory fish and even though humans bread them for generations feeding pellets their natural instincts never went away just dormant until a snap
I'd say if u're keeping bichir or any monster variety for that matter keep them with similar ones or keep them solitary
Putting a predator with prey will never go well

 

[GaryE]

With all due respect to your friend, because he/she has made a common mistake - a little tiny bit of time on research would have avoided this. A Senegal bichir grows to around 16 inches, and is a predator. If it's 5 inches now, that's meaningless. Now goes away quickly. It's going to predate, and all those fish will be eaten, in time. It isn't being aggressive, it's just being what it is.

No fish stays the size you wish it would stay. If you don't abuse it, it will grow to its potential. That includes its mouth growing, and if it's a predator, then its food choice will expand as it does. Its companion fish are trapped in a glass box facing death, once it starts. It isn't going wild. It's going normal. It's predictable.

I've learned to always look up the maximum adult size of any fish that interests me. I'm an experienced aquarist, so chances are the fish will get there. I won't buy a fish I'll have to kill later, and no one rehomes the big ones. Stores smile, take them back and hit them with a hammer in the back room, telling you someone asked for them. It's all they can do. The good stores hate it.

So, this is all harsh I know, but it is what it is. It's choosing doom now. Who loses, the other fish in the tank, or the bichir?

There is one way out. A new, expensive fully equipped large75 gallon plus tank for a pet fish that should have been kept in an appropriate community, or alone, from the start. They're mighty cool looking, but so are baby skunks, and if you want one, you have to be prepared for both the good and the bad.

 

[SammyTargo]

I appreciate all of the responses. I also suggested to my friend that he should join this community himself as he is a good and experienced fishkeeper as well (everyone makes mistakes, I would think I have made more than him ).

I informed him what you guys said word for word (and the photo from @Magnum Man), and he said he did his research and the research said the tankmates would be safe. I can only wonder whether his research was similar to the search query that I put a few weeks back, about which tetras can be Jack Dempsey cichlid tank mates; the Gemini AI overview said JDs can go with Buenos Aires tetras, and Columbians. That would be partially true, as they would work as the most viable of all tetras to go as tankmates, posing the least risk compared to other tetras. A full sized JD even when bred in captivity may still predate on them at full size, and they will only be safe tankmates during the JDs' growout phase. Same would probably apply to Bichirs as they would be timid around all of those tankmates until they aren't.

I have never kept a bichir or nearly anything of the sort, I prefer community setups and I don't really always agree with keeping predatory large fish in aquariums; in their natural environment they often traverse around large areas and IMO it is unfair to keep them in any confined space less than a large pond. I did my research after reading your responses and reporting back to my friend. Turns out just as I expected, I was initially blown with an AI overview claiming they can but there is a general risk with a bunch of "ifs and buts."

For me it comes down to prices. If it comes to saying good riddance to the community or the predator, it would be the community for me. He already exclaimed how he doesn't want to lose 12 healthy and grown out tetras bought at $20CAD each to 1 singular $15 bichir... I would assume much less kribs which reach a similar max length to the congos, and S. Petricola which ironically reaches yet the same approximate full size (slightly bigger but in this scenario the adult bichir wouldn't care ).

Look, the final decision will be ultimately in his hands. Me and others' advice will only influence it. I had told him that he should trust your opinions as I know you guys are very trustworthy. I explained that I would rather trust other experienced fishkeeper's advice that have been doing this for a long time and are genuine, over a website or YouTube video with a most likely biased opinion trying to sell/influence someone to purchase something. Even without it these are personal experiences from people who have learned stuff first-hand.

As of last night he attempted to catch the bichir and put it in a floating algae container with holes in it; and he was going to decide today what to do ultimately. He informed me today he could not catch it and had tried for 2 hours straight. I have seen the tank, and it has multiple large pieces of wood and hardscape which could prove to be very tedious to maneuver around with a net. I would assume the danger in the tank is still largely minimal because the bichir had caught the tetra completely off-guard in a vulnerable scenario. I will try to help him devise a plan during this grace period where the bichir cannot easily hunt the other fish yet.

The main things I think are important to figure out that you all can help me find out (most are hail marys that would probably be unrealistic, but for the sake of possibility and theory):

• Is there stuff he can do long term?
• Although not ideal at all, I assume my friend would not be eager to get rid of the bichir, so as an optional approach what are some tankmates that would not be predated on (large cichlids/equal predators that would respect the bichir, or ones that the bichir should not bother)?
• If he were to rehome the bichir in it's own tank, how big? I may be wrong but I think he had a 40 gallon that he is yet to setup; it would probably be a bummer for him to put the bichir there instead of doing the new tank idea he was thinking about, but if a 40 is sufficient, I'll propose it to him.

Sorry if that was a huge mouthful, and thank you again for anyone and everyone who is giving advice and recommendations,
Samuel

 

[Magnum Man]

I can only speak for my bichir, but it used to take him a week to catch 20 feeders, and in between he would go around and kill them, but not always eat them right away… hunting is learned, and their eye sight weak, but this last time 20 medium sized comet gold fish completely disappeared in 2 hours, so he has become a better hunter, and at his size, can stuff 20 mid sized gold fish in his stomach at one time… just the fact that he could eat a pleco 80% of his own size, should give a person pause, as to what they are capable of…

 

[Magnum Man]

your friends fish has the potential to get twice the size of mine… so at adulthood, the 70 gallon is too small for the bichir alone… I bought a smaller variety, as it’s home is a standard 55 gallon…

 

[GaryE]

I love the look of bichirs, and know they are extremely popular fish right now. For some reason, predators are in fashion for 2026. I think your friend's mistake is one we're going to hear a lot of in the next year or so.

I was thinking of the old advice online about dempsies when I typed my response. You would have sworn they had no mouths when you read some of it. But the old rule - big fish eat little fish holds true. Even if the bichir is a slow hunter with minimal skills to start, the fish in with it are going to understand it's a predator as they watch it. Imagine the stress levels when we do that to them.