5 Techniques for Catching Fish in a Marine Aquarium

At one point or another, every marine aquarium hobbyist is faced with the necessity of capturing and removing a fish from a fully operational system—perhaps because the specimen is bullying tankmates, the victim of another specimen’s bullying, sick or injured, etc. Whatever the reason, the prospect of catching a fish that has “home field advantage” in a functioning, aquascaped aquarium can seem daunting—sort of like capturing a chipmunk in a woodpile.

Chasing the fish all over the tank with a net will only stress the specimen and put it at risk of injury as it dashes around frantically, attempting to evade capture. Removing all the live rock and other aquascaping isn’t necessarily a practical solution either, especially if you have a reef system full of corals.

The good news is, there are many different techniques you can use to capture a fish without turning your whole aquatic world upside down. Here are five examples:

#1: The Two-Net Takedown

If you have sufficient room to maneuver in the tank and the fish hasn’t already “gone to ground” in the rockwork, you can try the Two-Net Takedown. This technique, as the (completely fabricated) name implies, involves the use of two fish nets. The first is utilized not to chase down and nab the specimen, but to encourage it to swim away in the opposite direction—and hopefully right into the second net that you’ve strategically positioned in its line of escape.

You’ll probably get only one shot at the Two-Net Takedown because the fish will very quickly get wise to your intentions and will hide in the rocks as soon as a net comes into view.

#2: The Nocturnal Nab

A few hours after dark, when the sought-after specimen is resting and sluggish, can be a great time to bring a net to bear, but only if its sleeping quarters are relatively easy to access. For instance, the tomato clownfish in my 125-gallon tank always rests in one particular top corner of the tank right next to the overflow chamber. If ever I should need to capture it, I could net it out after dark in seconds. However, if the specimen sleeps ensconced in a live-rock hideaway, this method isn’t going to work.

Patience is key with the Nocturnal Nab because you don’t want to attempt it immediately after lights out. You want to wait until the specimen is good and relaxed and dreaming its little fishy dreams before making your move. Also, “spotlighting” the specimen with a flashlight beam just before deploying the net will disorient it further and facilitate easier capture.

#3: The Baited Trap

If netting isn’t practical or successful, you may want to try setting a baited trap for the fish. There are commercially manufactured traps of various designs on the market that you can buy, or you can construct a simple, inexpensive DIY trap out of a common plastic soda bottle. Here’s how:

Using a sharp utility knife or razor blade, carefully cut off the top (approximately) one-third of a thoroughly rinsed two-liter soda bottle. Then, invert the top portion of the bottle into the bottom part so the threaded opening is facing downward. To secure the pieces together and prevent the top part from falling inside the bottom part, apply a few small dabs of aquarium-safe-silicone or super glue gel where the two sections meet. After the adhesive has dried, bait the trap with a sinking food that you know the fish will eat and place the trap on its side at the bottom of the tank.

Note: Depending on the size of the fish you need to capture, you may need to widen the opening of your DIY trap.

Again, patience is a must when using the baited-trap method because it may take several days for the specimen to get accustomed to the trap being there and to feel confident enough to venture inside. Then again, some fish are just too savvy or suspicious to fall for this ruse.

#4: The “Toto, I’ve a Feeling We’re not in Kansas Anymore” Technique

Okay, that name is really a stretch, so please bear with me. Essentially, this technique involves removing the entire rock in which a specimen is known to be hiding, transferring it to a rigid container under water, and then moving the fish, rock and all, to its new home—sort of like Dorothy being swept away to the Land of Oz by the tornado (see, I told you I’d bring it back around!).

In order for this method to work, however, very specific conditions must be in place: The fish must be hiding in a cave, nook, or cranny in a single chunk of rock (for instance, I once had a flame angelfish (Centropyge loriculus) that, at any sign of danger, would tuck itself headfirst into a very narrow “pocket” on the underside of a piece of live rock), and the rock must be easily accessible without tearing apart the whole pile.

#5: The Recession

Sometimes there’s nothing for it but to deprive the fish of at least one advantage—the ability to escape in multiple planes. By this, I’m referring to lowering the water level in the tank almost all the way to the bottom to tip the odds of a successful capture in your favor.

As you might imagine, this method is not ideal for reef systems, as it would leave most or all of the corals high and dry (some species are more or less tolerant of air exposure than others). Even in fish-only or FOWLR (fish-only-with-live-rock) systems, this technique needs to be performed quickly and efficiently so the rockwork is exposed to air for only a brief period, thus ensuring that the biofilter isn’t compromised.

The best way to expedite the process is to use a hefty submersible pump and tubing to rapidly transfer water from the tank to a separate container and then back again.

What’s your secret?
If you have a technique for capturing fish that isn’t described here, we’d love to hear from you! Please share your idea with your fellow salties in the comments section below.