How to Catch a Fish in a Reef Tank Without Removing Rocks

Every reef aquarium owner hits this sooner or later. A fish turns aggressive, gets sick, or just has to move to quarantine. The second a net touches the water, it disappears into the rockwork, and pulling the rock apart means stressing every coral you own over one fish.

The good news is you can get it out without touching the rock. The trick is to stop chasing the fish and take away its options instead. Below are four methods that work, what each one costs you in time and effort, and which fish each suits best.

The best way to catch a fish in a reef tank: quick comparison

Short answer: for a fish that stays in the open, two nets is fastest. For a fish that hides in the rock or ignores traps, give it a shelter you control (Method 4).

best · · · · worst, in every column (for effort, means the least effort). Overall adds up all five columns, cost included, for a fish that hides in rock.

Before you start

A little prep makes any method faster and easier on the fish.

• Have the destination ready. Quarantine tank or holding container filled, heated and matched to your display before you touch the fish.
• Turn off pumps and wavemakers. Still water lets you see the fish and stops it riding the flow away from you.
• Skip a feeding. A slightly hungry fish is easier to bait and more likely to come out.
• Know where it sleeps. Watch at lights-out for a night or two. Most fish go back to the same spot.
• Move slowly. Every failed attempt teaches the fish, and the next one gets harder.

Method 1: Two nets and the lights-out trick

Cheap and fast, but you usually get one good shot. Use one net to block and push, and the other to catch. Herd the fish into the second net rather than swiping at it.

The lights-out version helps: wait until the tank has been dark a while, then hit the fish with a torch. It's briefly dazed, which gives you a few seconds to net it.

• Good for: clownfish, chromis and other fish that stay in the open.
• Downside: miss once and the fish gets net-shy, and it's hard to do on your own. Fast fish like tangs and wrasses rarely fall for it twice.

Method 2: A baited trap

The classic hands-off option. A clear box or a cut-down drink bottle goes in with food inside, and a door or a narrow neck stops the fish getting back out.

The catch is the wait. Most fish need several days before they trust a new object enough to go in. Reefers often report weeks of waiting to trap a single fish, and the complaint that comes up again and again is "I've caught every fish except the one I want." Some trap-wise fish never go in at all.

Traps also catch whatever goes in first. Unless you sit and watch, ready to close the door on the right fish, you end up fishing out the wrong one.

• Good for: fish that are food-driven and not in a hurry to leave.
• Downside: slow, and territorial fish like damsels and dottybacks often treat the trap as an intruder rather than a meal.

Method 3: Shrink the space

If the fish has too many places to hide, take some away. Drape a plastic bag over the rockwork so the fish can't slip between the rocks. If the rock stack is too big to cover, stuff plastic bags into the caves and crevices the fish is likely to duck into instead. Then slide egg crate across as a divider, push the fish into a smaller open area, and net it in the corner.

The heavy version is draining the tank down to a few inches so the fish can't swim freely. It works, but it exposes your corals and takes hours to refill and settle.

• Good for: big tanks with lots of rock, and fish that have already learned to dodge nets. It also pairs well with Method 4.
• Downside: needs patience and often a second pair of hands. Draining is a last resort.

Method 4: Give the fish somewhere to hide

This method flips the usual problem around. A fish under pressure looks for cover, which is why it bolts into the rock. Give it a better hiding spot, one you control, and it swims in on its own.

That's the idea behind the AquaCove, which we make at FITC Aquatics. It's a dark acrylic cave. You place it in the tank, gently herd the fish toward it, and the fish ducks inside for shelter. There's no bait and no days of waiting for the fish to get used to it, so you can use it the day it arrives. An optional mirror attachment helps with territorial fish, which go after their "rival" and end up inside.

Speed depends on the fish. In my own tanks, wrasses and tangs usually go in within 5 to 10 minutes, and medium fish like squirrelfish and rabbitfish take 15 to 20. Groupers are the toughest: my latest tomato grouper and blue line grouper took up to an hour of slow herding before they ducked inside. That still beats days of waiting on a trap, and I didn't have to move a single rock.

The grouper catch is edited down. Groupers like this one can take up to an hour of slow herding.

• Good for: fish that hide in rock, dodge nets or ignore baited traps, including tangs, wrasses, damsels and dottybacks.
• Downside: you still have to herd the fish, so it isn't hands-off. It's sized for larger tanks (assembled: 36.5 × 32 × 18.5 cm, about 14.4 × 12.6 × 7.3 in), so check the fit in a small or shallow tank.

The AquaCove in a 5ft, 110-gallon reef tank, and held for size (assembled: 14.4 × 12.6 × 7.3 in / 36.5 × 32 × 18.5 cm).

Which method for which fish

In a rock-heavy tank, combine Methods 3 and 4: block off the biggest caves first, so the AquaCove is the nearest cover when you start herding.

FAQ

How long does it take to catch a fish with a trap?

Usually several days, since the fish has to trust the trap first. Trap-shy fish can take weeks or never go in.

Is it bad to chase a fish with a net?

A few tries won't hurt, but repeated chasing stresses the fish and its tankmates. Each miss also makes it harder to catch next time.

Should I drain the tank to catch a fish?

Only as a last resort. It works, but it exposes your corals and invertebrates and takes hours to put right.

Can I catch a fish at night?

Yes. Fish are slower in the dark and go back to the same sleeping spot, which makes the lights-out trick and herding easier.

Does a red light help catch a fish?

It helps you watch without spooking it. Many reef fish see red light poorly, so a red torch lets you find where a fish sleeps. It won't make the fish any easier to net on its own.

What if the fish hides as soon as I walk up to the tank?

That's the hardest case for nets and traps, because the fish has learned you mean trouble. Move slowly and stay low. A shelter works here because the fish goes in to get away from you, rather than having to come out for bait.