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10 Smart Ways to Use an Aquarium Catch Cup or Specimen Container

Have you ever seen those clear rectangle boxes hanging on the outside of tanks at your local fish store? You are looking at one of the most versatile tools in the fish keeping hobby – the aquarium specimen container or catch cup. It acts like a small, transparent bucket for observing fish, holding aquarium supplies, and a million other uses. Learn about the top 10 ways we find ourselves using catch cups every day at our retail fish store and personal fish tanks.

1. Observation

It can be hard to really see your fish when they are zooming around an aquarium or darting behind decorations, so to get a closer look, catch a group of them with a fish net and place them in a catch cup full of water. The smaller space allows you to inspect the fish for disease symptoms, pick the healthiest individuals for breeding, or sort out male and female juveniles for sale. Plus, the clear, flat walls are perfect for photography so you can proudly show off your favorite species.

2. Transportation

Aquarium nets may be fine for moving a few fish from one tank to another, but this method can be quite inefficient if you have a large school of fish to transfer. Instead, use your specimen container as a temporary holding pen until you finish catching all of them and then move them together afterwards. You can relocate fry to a grow-out tank to prevent them from getting eaten by predators, bring pond fish indoors for the winter, or remove pest snails in one tank to feed to your pufferfish aquarium.

Guppies in Aquarium Co-Op Catch Cup


3. Selling Fish

If you plan on selling your fish at a fish store, fish club auction, or online, you usually need to package the animals into fish bags. Scoop out some aquarium water and then place the fish you catch into the specimen container. Once you have the right number of fish, you can easily pour them from the catch cup directly into the fish bag and then seal them inside with rubber bands. You can even use multiple containers – the first one to hold a large netful of unsorted fish and the secondary ones to separate out the right number and species for each fish bag.

4. Acclimation

If you are buying new fish or shrimp, they may be accustomed to water parameters that are very different from yours, and therefore you may want to slowly acclimate or get them used to your aquarium water. If the animals are small enough, you can acclimate them in the specimen container.

  1. Cut open the fish bag and pour the animals and some of the water from the bag into the catch cup so the fish are completely covered in water.
  2. Add aquarium water from their new home into the catch cup so that the water level is doubled. (If the water gets too high, just pour some out of the container.)
  3. After 15 minutes, add more aquarium water so the water is doubled again.
  4. After 10 minutes, add more aquarium water so the water is doubled again.
  5. Net the fish out of the container and add them to the aquarium.

For an even more gradual acclimation process, look up how to do “drip acclimation” using a length of airline tubing. If the fish are frantically dashing around in the catch cup, you can calm them down by darkening the room and/or covering the container with a towel.

5. Breeding

You can make your own DIY breeder box with a catch cup by adding an air stone, check valve, airline tubing, and air pump. Hang the specimen container inside the aquarium to keep it warm if needed, and add the air stone to make sure the fish get enough oxygen in the water. Then you can place a select pair of fish inside to increase the chances that a certain male and female will mate together. This simple setup can also be used to hatch fish eggs that need a few drops of methylene blue to prevent fungal growth. Finally, you can temporarily raise newborn fry inside a catch cup without worrying that they (or the tiny foods you feed them) will escape. Add a clump of java moss or other live plants to give them shelter, and make sure to frequently clean out the dirty water inside using a turkey baster.

baby fish in catch cup


6. Isolation

There are several situations where you may need to temporarily separate one fish from the rest of the crowd. For example, female guppies, mollies, or other livebearers that are about to give birth may appreciate a quiet and peaceful environment to release their babies. Setting up a “birthing room” will protect the fry from getting eaten immediately by bigger fish, and adding a clump of plants inside will help the newborns hide from their own hungry momma.

Another case would be to isolate a fish that has an injury, is behaving oddly, or exhibits other strange symptoms. Keeping them in a specimen container with an air stone allows you to monitor their status more closely and potentially treat them with medication if needed. For more information on treatment of fish diseases, read the full article.

betta fish in catch cup


7. Mealtime

We always recommend feeding many different fish foods to ensure your fish get a variety of essential nutrients, but it can be hard to juggle all those round jars and slippery packages. Use your catch cup as a portable food tray to carry everything as you move from tank to tank. If you are feeding frozen foods, thaw the cubes in water inside the specimen container and use a pipette or turkey baster to squirt the liquid into multiple aquariums. The same technique can also be used with live fish foods like baby brine shrimp, blackworms, daphnia, and infusoria. 

8. Water Transfers

As mentioned before, the catch cup is like a mini bucket, so we often find ourselves using it to quickly remove surface scum from an aquarium or replace water that has evaporated from a nano tank. If you want to test your water parameters using liquid reagents, scoop up some tank water with the specimen container and then use a pipette to fill the test tubes. During water changes, some hobbyists will place their catch cups inside the aquarium and then stick the end of the hose or aim their Python hook into the container while refilling the fish tank. The incoming water gently overflows out of the catch cup, preventing your plants and substrate from being disturbed by the force of the faucet.

fertilizer and tweezers in catch cup


9. Equipment Storage

Whenever using fish nets, algae scrubbers, or other tools in the aquarium, a specimen container is the perfect place to put them afterwards so they don’t drip all over the floor. Many people use them as extra storage space by hanging the catch cup on the side of the fish tank to keep their favorite fish food, fertilizers, and other supplies all within easy reach.

10. Planted Tank Maintenance

One of our favorite uses for specimen containers is during the maintenance of planted aquariums. Use them to remove duckweed and other floating plants that have taken over your aquarium so you can spread them to other tanks or feed them to your goldfish. While pruning, put your stem plant trimmings in the catch cup, and then replant them in the substrate to propagate them.

aquarium plant trimmings in catch cup


Now that you know you need to have a specimen container in your life, make sure to get the Aquarium Co-Op Catch Cup. The walls are very clear so you can easily view your fish, and the shatter-resistant plastic won’t break when accidentally dropped. Plus, the extra-wide handle allows you to hang it on large fish tanks with thick walls.

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