Every single aquarist on earth, probably, has had problems with this issue. I remember myself chasing the poor devils for half an hour around the tank. Eventually they would end up inside the net, exhausted and stressed. And I would end up on the other side of the net, exhausted and stressed. For both parties involved, a very, very uncomfortable experience.
is unavoidable in this hobby. Some of the reasons are: when giving away/buying/selling a fish, moving a sick fish into a quarantine tank, moving parental fish together with their fry/eggs into another tank, trying to get the aggressive fish back to the pet shop, etc.
One thing you should avoid is lashing with the net around the tank in pursuit of the fish. It will harm/stress all the inhabitants of your tank. And it is very possible that you will end up not catching the fish you want.
The best thing to start with is to empty some of the aquarium water. The less space for the fish - the greater possibility for you to catch it in a short time. Here are few tips on how to get your beloved pet out of the aquarium as painlessly as possible.
Catching with a net
is the most common way among aquarists. Nets come in many sizes and colors. White nets are not as affective as the black or green ones, that give the fish a false feeling of security. But since a fish would rather swim away from a white net, it can be used for directing the fish towards the other black/green net where the fish is going to seek refuge. When doing this, moves must be gentle. The fish will eventually go into the black/green net by itself, guaranteed! This way the rest of the inhabitants are spared of being stressed out as well as the caught fish. Note: if the fish's fins get entangled in the net, don't panic! The best thing to do is put the fish back into the tank, hold the net with one hand and let the fish free itself. If this doesn't happen, the only solution is to get sharp scissors and carefully cut out the net.
Catching with your hands
is another method used with larger fish. This has to be done carefully, because some species - like Loaches or Catfish - have spines for defense. Don't get spiked! With one hand, gently grab the fish just before the tail while the other hand (flattened) is supporting the fish from underneath. All this has to be done with enormous patience. NOTE: do not handle this way fish that are poisonous or that have high-voltage electricity!
Catching with a bottle
is one of the ways to catch certain smaller bottom dwellers like Kuhli loaches, shrimp, and snails. The bottle should ideally be light-green so you are able to see what is inside and the color will provide false security for the fish. Before placing it in the tank, the bottle has to be rinsed well in warm water. The bottle should not be cleaned with detergents of any kind! A glass bottle is a better choice than plastic, as it will readily sink to the bottom. Place a sinking tablet food inside the bottle and sink it, by slowly allowing the water to fill it up. Once at the bottom, lay the bottle on the side so that the opening is touching the gravel surface. After that, all we have to do is switch the tank lights off and wait for the desired fish to enter the trap. It is good to have some kind of room-light on. If you have live plants, then the best time to switch off the lights is the evening hours. When the fish is trapped, approach the bottle gently not to scare the fish, and close the entrance with one finger. This method requires patience and it might take a few days to catch the desired fish, but will definitely save your fish from stress. With this method the aquarium water depth can stay as usual. There is no need to remove water. NOTE: be careful not to hit the aquarium glass while handling the bottle.
Catching with glass dip tubes
is not a very popular method these days, except with breeder-aquarists that need it to catch the fry without hurting it. Ask your dealer for more info about this device.
It takes time to become a skilled "fish-catcher", but it is not impossible :D .
I use a styrofoam cup to catch the fish. I put a little food in the cup and it goes to get the food. The cup is dark, so it looks like a cave and no stress is caused! For jumpers (ex. Betta splendens), use your hand to cover the top provided that your fish don't bite!
In addition to lowering the water level, I use a tank divider to corner the fish in one area of the tank. I have a divider for a 20G long, I've never used it in my 20G, but it comes in handy when I need to catch fish in the 55G, as it makes for a much smaller space.
I catch my bettas by hand sometimes. They have become quite familiar with this technique and don't get as stressed as I thought they would. When I use the net on any fish, I move it slowly and gently herd the fish towards the glass wall. I then place the net so that the net and glass trap them. I then pull up. This guy at the fish store was trying to catch my new dojo loach by taking a net and whipping it around after him. After he left for a bigger net I took the one he had and caught the quick little guy in just a few seconds by gently moving the net. If you frighten fish they will do all they can to avoid you. Just don't be threatening. It works wonders.
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