Lake Malawi Species • Tips for Removing Aggressive or Rejected Fish?

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Tips for Removing Aggressive or Rejected Fish?

Postby dolfan1980 » Thu Jul 16, 2020 3:19 pm

My 75 gal is working relatively well, but I do have a rejected yellow lab and an aggressive cobalt blue zebra that I would ideally like to remove and see how the dynamics change. Things aren't that bad, but reading here it is probably the right thing to do. The reality is that I would probably need to rip my tank apart to catch them and even then I have no idea after they all move about which one is which. I don't really want to take everything out of my tank to catch potentially the wrong fish.

Any tips?
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby Deeda » Thu Jul 16, 2020 3:27 pm

The usual suggestion is to wait a couple hours after tank lights out or night time when the fish are sleeping or more relaxed but if the bullied fish don't isolate from others at this time, it will be difficult to catch them.

I've never had any luck catching a specific fish so hopefully someone else has better suggestions.
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby dolfan1980 » Thu Jul 16, 2020 3:34 pm

Glad to hear I'm not the only one who finds the prospect difficult.
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby ken31cay » Thu Jul 16, 2020 4:05 pm

Except for the times I got lucky and snatched a fish at the top who thought it was feeding time, I've had to remove all or most of the decor.
In addition I would either:
1. Remove most of the water and use my large net, or
2. Leave the water and make the room very dimly lit for 2-3 hours while keeping everyone out of that room so the fish will relax/sleep, then quickly with no sudden movements or noise net the fish.
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby sir_keith » Thu Jul 16, 2020 5:22 pm

Ah, the age-old problem. I've tried many things over the years to facilitate the removal of one specific fish from a large tank loaded with rockwork, or even worse, live plants. The method that works for me is to use temporary tank dividers.

Consider a simple case- you have 25 fishes in a 6-foot tank, and want to remove one specific fish, for whatever reason. Even if the tank were totally bare- no substrate, no rockwork or decorations of any kind- you still often end up chasing the fishes from one end of the tank to the other. Now imaging there are tank dividers in place that divide the tank into thirds. The fish you want will necessarily be in one of those thirds, only 2 feet long, together with (on average) 7 other fishes. Much easier task. So how to make this work in the real world?

Plastic mesh canvas- used for needlepoint and other crafts- is inexpensive and fits the bill nicely: it is flexible enough to fit into your tanks, but stiff enough to stay in place once positioned properly. One 12" x 18" sheet is perfect for a 55 gallon tank; two of those sheets, taped together to form an 18" x 18" square, work for a 125.

IMG_0676.jpg


You can buy these on Amazon for ~$2 per sheet-

But your tank is full of rocks, right? Well, if you've been clever, you positioned your rocks so there are two or three places along the length of the tank where you can install a tank divider without disturbing anything at all. You may still have to move a few rocks once the tank dividers are in place to catch your fish, but only in 1/4 or 1/3 of the tank.

I've been using this approach for quite a while, and it works for me, both for rock-dwelling fishes (Tropheus) and sand nesters (Xenotilapia; Ophthalmotilapia). With the sand dwellers, it's even more important not to disturb things, because I don't want to destroy weeks of work by the dominant males in establishing territories and building sand nests. Even in a tank that contains both rocks and plants, like that shown below, my tank dividers work fine. If you look closely at this tank, you will see that there are two places where tank dividers can be inserted, dividing the tank into thirds. Good luck! :fish:

IMG_0112.jpg
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby DJRansome » Thu Jul 16, 2020 5:34 pm

If I try not taking everything out of the tank...I always end up doing it anyway and being unhappy about it.

So I started just taking out the rocks up front and it is really not so bad. It's just the idea of it.

I do aquascape with 3 rockpiles so I can shoo all the fish to one end. Divide the tank and remove 1/3 of the rock. Drain half the water and use 2 large nets.

I have no luck with the capture during sleep.
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby sir_keith » Fri Jul 17, 2020 10:43 am

DJRansome wrote: ... I have no luck with the capture during sleep ...


Same here: I'm useless with a net unless I'm awake... :o
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby aconite » Fri Jul 17, 2020 12:20 pm

I haven’t been doing it for very long, but I’ve only successfully caught fish by using dividers, removing rocks, and also draining half of the water.

With two dividers I can usually get the target fish into a pretty small area of the tank and then just net it.

It always turns into a fairly major operation so it’s best to resign yourself to the fact up front, as DJ says.

Never managed to net a fish from near the surface without dismantling the rocks - they see the net and just scatter into the rock work.

I’ve also learnt to put any removed rock into containers holding tank water. Catfish like clinging on despite all attempts at shaking them loose!
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby DJRansome » Fri Jul 17, 2020 4:00 pm

aconite wrote:I’ve also learnt to put any removed rock into containers holding tank water. Catfish like clinging on despite all attempts at shaking them loose!
Plus one. I have found plecos in hollow decor items with virtually no water 24 hours later that lived to tell the story.

I have been surprised by calvus in supposedly empty shells 24 hours later in cold water that were fine because of the bucket of water process. You put your hand in the bucket of inanimate objects and something big starts flipping around!
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Re: Tips for Removing Aggressive or Rejected Fish?

Postby dolfan1980 » Fri Jul 17, 2020 4:11 pm

Thanks for all the tips!
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