Rainbow shark getting really really aggressive

Hello I'm in need of a bit of help... I have got a rainbow shark in my 117 litre tank.. it's only a baby... so not very big at all.. it has been fine in my tank... it's never ever bothered any other fish in there... it was really happy in my tank.. got along fine with his tank mates... but for the last 2 days he has got very aggressive with all the other fish.. constantly chasing them... but in a really nasty way.. I'm almost certain I have seen it trying to take chunks from other fish... I could be wrong but that's what it looked like... does anyone know why this could be happening? I've tested my water just now.. my water is fine.. so it can't be that... he was really happy and all of a sudden he has turned really nasty... has anyone got any suggestions for me please would really appreciate it

This is not really surprising, as it is in the DNA. While the Rainbow Shark (Epalzeorhynchos frenatus) is sometimes somewhat more docile than its cousin the Red Tail Shark (Epalzeorhynchos bicolor) it is not guaranteed. This fish needs more space than a 117 liter tank, though presumably young now but it will grow. And for reasons we do not understand individual fish can sometimes take a real dislike to certain upper fish. I would suggest you re-home this fish immediately. The stress the other fish are undergoing will cause them to weaken and develop problems that could and should be avoided.

I have never kept them myself, but I know a few people who have had them tell me they can be very territorial. This usually will happen when the fish begins to mature, so the fish has probably reached the Size or age of maturity.

Thank you for the advice.. maybe I will have to get him a new home... the pet shop did say that the shark would chase other fish... so I was expecting it... and they said it was fine that's just how a shark acts .. and that my tank was big enough to keep one.. it is at the minimum size they said... so when I got it if it was doing this straight away I probably wouldn't be concerned to much... as they said it would chase fish.. but I'm only concerned as the shark was so peaceful... and didn't bother other fish at all... but suddenly he has changed...

Ryan231211 said:

and they said it was fine that's just how a shark acts

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that's poor advice from a LFS, it may be fine for the shark, but cause unnecessary stress and death in the fish held with it.

Ryan231211 said:

and didn't bother other fish at all... but suddenly he has changed...

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It will have started to mature, a lot of fish species will become more territorial when they begin to mature.

Right I see.... so I'm guessing I'm going to have to try find a pet shop that will take it then... so is this my only option... to get rid of the shark? I really want to keep him as he looks great in my tank... but don't want to be the cause of fish dieing... it's mostly the tiger barbs that the shark is going for... I was told that a shark and tiger barbs was a good match for tank mates.. as the barbs can easily stick up for them selves.... is this not the right information?

Ryan231211 said:

Thank you for the advice.. maybe I will have to get him a new home... the pet shop did say that the shark would chase other fish... so I was expecting it... and they said it was fine that's just how a shark acts .. and that my tank was big enough to keep one.. it is at the minimum size they said... so when I got it if it was doing this straight away I probably wouldn't be concerned to much... as they said it would chase fish.. but I'm only concerned as the shark was so peaceful... and didn't bother other fish at all... but suddenly he has changed...

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The chasing of fish around the store tank, netting and bagging the fish, and then introducing the fish to your tank...all this is extreme stress for the fish. It invokes the predator flight response in the fish, and that is as bad as it can get. Which is why ich can be so common in newly acquired fish.

But this explains why the fish may be "different" at first. It has been severely stressed and now is settling down into a completely new and strange environment. Some fish do this remarkably fast, others not. It can bee weeks, even months, before the fish's normal behaviours begin to show up. Many assume at first that the advice they read was wrong and all is well, but this state of euphoria seldom lasts if the fish is healthy. A stressed fish, and this can become permanent, may never exhibit normal behaviours. But other fish may recover in time and then begin to act normally, and in this case with a normally semi-aggressive species, this can wreak havoc.

It is not unlike the behaviours we see in children that are moved to a new environment, say a new school, or a new location. At first they may be withdrawn, quiet, almost fading into the background, especially if none of their former friends are present.

Ryan231211 said:

Right I see.... so I'm guessing I'm going to have to try find a pet shop that will take it then... so is this my only option... to get rid of the shark? I really want to keep him as he looks great in my tank... but don't want to be the cause of fish dieing... it's mostly the tiger barbs that the shark is going for... I was told that a shark and tiger barbs was a good match for tank mates.. as the barbs can easily stick up for them selves.... is this not the right information?

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Now we have more evidence...I mentioned previously that this "shark" frequently takes a dislike to certain upper fish. I didn't know what other fish you had, but the mention of Tiger Barbs tells a lot. Vertically-striped fish for some reason can really get a shark fish annoyed. This is more common in the Red Tail Shark, but not unknown in the Rainbow either.

To answer your question, you have only one option...separate the shark from the other fish. And since the shark will need larger quarters, it is best to remove it.

Rainbow and red tail sharks are vegetarian and some males will be overly aggressive when defending their territory. Most fish will simply guard their little patch of algae but others can take over the tank. If you have lots of hiding places, caves, driftwood, plants, etc in the tank, the shark will usually be less stressed and less likely to harass the other fish.

Sometimes the fish settle down but sometimes they don't. You can try adding lots of plants and hiding places and see how he goes. If he is still a nuisance in a couple of months then move him out.

Make sure he is getting enough food. If he is hungry he will defend his territory more aggressively. And if other fish (like the tiger barbs) are picking at the bottom feeding foods that are meant for him, he will get more upset with them. You can usually overcome this by putting a bit of food at each end of the tank so the tiger barbs go after one lot and the shark can have the other bit.

Right that is great advice.. thank you very much... I must admit I'm only feeding them once every 2 days.. and only a pinch of food.. so maybe he is hungry then... I will send a picture of my tank.. could you please tell me if it is okay for the shark.. it's not got loads and loads if hiding places.. not loads and loads of plants.. but deffinetly got places it can hide

This is my tank

Get some algae wafers from the pet shop and offer him half or quarter each day. If the tiger barbs go after it put another bit on the other side of the tank for the shark.

Put a picture on the back of the tank to make the fish feel more secure. Dark colours work best.

Is that an albino bristlenose in the picture?

You need driftwood in the tank for the bristlenose and the shark. They need a piece each.

You should increase the lighting times to encourage algae to grow on the glass and ornaments. You can have the light on for up to 16 hours per day but try 12 hours first and see how it goes. You want some algae growth or the algae eaters will starve.

Live plants might help too because the fish can graze on them. narrow Vallis would work well in your tank.

Funny you say that... I just got some today from shop.... did you see my tank? I has it got enough hiding places for the shark?

If you put some driftwood in each corner at the back, the bristlenose can have one bit and the shark can have the other bit where he currently lives (in the white rocks).

I reckon if you get more food in there for him he will settle down.

That's such a relief I will feed once a day and see how he goes... would be great if he settles down as I would love to keep him... wouldn't really want to give him a new home... as I think he just makes my tank...