How to solve a problem like trapping fish

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It may be difficult to catch the residents of a decorated aquascape or wood-tangled biotope. Here's how to do it…

Traditionally, two nets are recommended for catching fish. One net will act as the 'sheep pen' while the other is the 'sheep dog', guiding the fish into it. Fishkeepers using just one will generally take longer to catch a fish, increasing chase time and resulting in undue stress.

Nets can snag and create stress for other tank mates while the procedure takes place. An oft-touted claim is that if the net is left in the tank for a while before trying to catch the fish, they will get used to it. However, this is not the case, and the instant the net is moved the fish will see it as a threat and strive to avoid it.

Rounded nets are a bad idea, as many captures take place once the fish has been moved against the boundary of the glass. Facing a round design, a fish will quickly see the gaps and take them.

A trap may be preferable for truly problematic fish. The designs are similar to those used in the harvesting of some wild species, like Clown loach, but on a smaller scale.

A simple trap can be made using a plastic bottle, a pair of scissors and some bait food. Using a clean bottle, firstly remove the threaded neck, leaving an open hole.

If the top third is now cut off, it can be simply turned around and reinserted into the remainder of the bottle, creating a cone inlet with a small aperture. At this point the bottle can be baited with food dropped into the bottom, and resubmerged into the tank.

Be patient and observe when trapping a fish this way, as many wrong fish may be caught until the correct one eventually finds its way in. Once caught, remove the bottle and gently remove the top of the trap. You have your fish.

Life may be easier if some fishing line is attached to the bottle, allowing you to literally reel it out without having to submerge your ams.

Some traps work better in the open, especially when catching more active fish, although others should be strategically placed to mimic a cave for shy species like catfish. Try to time catch time with peak activity of the fish you want — daytime for tetra, night for cats.

In some cases, a feed-baited trap will not work — such as with mouthbrooding cichlids with young as they will refuse to feed.

Other fish behaviour can be exploited, such as territoriality and aggression. With a little ingenuity a small mirror, like a budgie’s, can be placed at the base of the bottle and visible from the opening. This technique works well in marine aquaria, where the fish may be a belligerent clownfish or dwarf angel. Unable to resist the threat to its territory, it will dive in to meet its opponent, only to trap itself.

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