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aggressive fish (1 Viewer)

MistakesWereMade

MistakesWereMade

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In my 40 gallon tank I have the following:
Aiptasia filefish
pair of mandarins
yellow assessor basslet
Mystery Wrasse

I recently added a small leopard wrasse (11/09/25). It was out swimming for about a day, but mystery wrasse was being aggressive towards it. It ended up hiding in the sand. I saw it a couple of times throughout the first week and every time I saw it out, I was offering food. I did a tank clean (11/16/25) and the leopard wrasse was out swimming around, but the mystery wrasse was hiding. Eventually it went back to hiding when the mystery wrasse came back out.

I decided to move the rock structures around (11/22/25) to try and lower the aggression and have the leopard wrasse out more but it has since gone back to hiding again. I did notice that when it was out during the layout changes it was looking fairly thin.

My initial thought is to move the mystery wrasse into a 10-gallon that I have set up for a little bit of time, then reintroduce it. I am looking for any other suggestions that may be helpful in this situation. I am a little worried that if I wait too much longer to do anything that the leopard wrasse will starve itself. Any other suggestions to this method? How long should I wait to reintroduce the mystery back?

There is always the option is to do nothing and hope it all works out. Any help/suggestions are appreciated.

I honestly didn't think the aggression was too much. I am not even sure I ever saw any actual contact between the two fish. And it was never constant. The mystery wrasse would just swim to the opposite side of the tank on occasion and the leopard would just be hanging out in the front corner of the display. My anthias are more aggressive towards each other than what is happening here, but this is a much smaller tank.
 
Tape a small mirror to the side of the tank. The aggressor will see its own reflection and tire itself out on that. After a few days you should be able to remove the mirror.
 
Ben Nicholls said:
Tape a small mirror to the side of the tank. The aggressor will see its own reflection and tire itself out on that. After a few days you should be able to remove the mirror.
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So far I like this idea. I will see what I can find to attempt it tonight. I would rather not have to pull anything out of the tank if I dont have to.
 
Mystery wrasses are unfortunately almost always like this 😭 I'm not sure taking him out would even do much once it goes back in it'll just be the same.

In the future acclimation boxes help a lot for new arrivals. Eliminates the issue where they just pound on new fish before they can get used to the environment. Might still happen a bit after they're released but at least they aren't already freaked out about being in a new tank too. They can be in the box for a long time, 1-2 weeks even.
If you quarantine first, I find it extremely helpful to do batches of at least 2 fish together so they can become 'buddies'. Once you put them in your display they feel comfortable around each other which helps with the stress - you'd be surprised how much they'll hang out together even if they're different species. It also spreads out aggression a lot.
 
I put a mirror on the tank yesterday when I got home from work. It certainly looks like the mystery wrasse could care less. It is probably a 5x7 mirror. I think I am going to try and find the leopard wrasse tonight and move it to a 10 gallon tank and see if I cannot get it eating well. If things go well and I can fatten it up I may consider reintroducing it in an acclimation box and possibly try another fish at the same time. It isnt a large tank but I think with how its set up it could work out.

10-gallon tank does not have sand. Do I need to add a bowl of sand?

I need to check salinity on the 10-gallon but if nothing else I could clear out some of my chaeto and house it in my 40-gallon refugium on my main tank.
 
Yes leopard wrasses need sand. A dish would be sufficient. I'm sure a refugium would work for it too, lots of bugs for them to eat.
Good luck!
 
Moved it to the refugium. Took awhile to find it in the sand. Moved every rock a few times before it came out. Was unexpectedly really easy to net. Need to move a dish of sand to it but I will try and do that tonight.

It will probably be in the refugium for a couple of weeks. Maybe I need to find something else to add to it than reintroduce in an acclimation box. Open to suggestions (either a process or attempted pairing).
 
I don't normally clean the sides so I had to scrape a bit or coraline off the acrylic just to see inside. It seems to be swimming around just fine and I was able to add a container of sand. Now I just need to do the extra bit of work to feed it everyday but there are plenty of pods in there.
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It has noticeably gotten some of its weight back and eats when I shoot in some mysis in. I have a good sized acclimation box I am going to be using to try and reintroduce it back into the tank. I am thinking of getting another smaller wrasse of some sort to add in at the same time.

If the mystery wrasse stays aggressive, I may just move it to my big tank. There it will be on the smaller size.
 
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