7 Types of Fish to Avoid if You’re a Beginner Aquarist

Beginner aquarists typically aren’t aware of the kinds of fish that often cause problems for maintaining a nicely balanced aquarium. Some fish get too big too fast. Others are overaggressive killers, unload a large amount of waste in the tank, or are prone to sickness. Fish that have more stringent and specialized water quality requirements or need better filtration are some other kinds of traits to watch out for if you’re a beginner. Here is a list of 7 fish species beginner aquarists should avoid, brought to you by Aquatic Warehouse, a trusted aquarium supplier.

1. Glass Catfish

These transparent fish are pretty awesome because you can see through their entire bodies. They’re often kept in groups of six or more. The big problem with the glass catfish (or glass cat) for beginner aquarists is that they’re highly susceptible to bacterial infections and are likely to perish in a community tank if not cared for properly.

2. Pacu

Pacu is a common name used to refer to a species of omnivorous South American freshwater fish that are often sold as the vegetarian cousin of the piranha. These fish are sold when they’re only 2 to 3 inches long. Watch out though, as the pacu fish will generally outgrow a 55 gallon tank in the first year and continue growing to over 10 pounds (and their pretty colors will fade as well). At Aquatic Warehouse, we don’t sell this fish for the reason that a lot of stores can’t take them back when they get too big. As a result, customers dump them in local waterways, which isn’t good for the fish or the environment.

3. Discus

The discus is one of the most beautiful aquarium fish in the world. It’s also very peaceful and docile, displaying a calm demeanor. However, the discus isn’t good for beginners since it needs extremely specialized care compared to most other beginner community fish. It requires very specific water parameters, a large tank with several exclusive fish-mates, and a regular and strict water change schedule. Accordingly, discus fish should only be considered for intermediate and advanced aquarists.

4. Red-Tailed Shark

The red-tailed shark is a very popular fish because it has stunning coloration and a shark-like body. It’s not a good fish for beginners because of its territorial nature, especially if it’s kept in the tank with other red-tailed sharks or similar shark species. Also, they’ve been known to harass smaller fish in community aquariums. Even if you have fish who aren’t so small and don’t scare easily, the red-tailed shark could still terrorize them.

5. Koi

Koi are essentially a beautiful carp that can grow to 2 feet long and weigh several pounds—100 to 200 gallons of water is needed per adult fish. They’re typically found in water gardens and backyard ponds because that’s where they were meant to live. Though they can be kept in an aquarium initially, be ready to move them outside after a couple of years.

6. Oscar

Oscars are very popular and widely available. They’ll need a specialized aquarium for large fish that’s 50 gallons or more. Also, the oscar is very aggressive and has a tendency to eat any kind of fish that will fit in its mouth.

7. Silver Arowana

The silver arowana is another “tank buster” fish that eats all the other fish around it. This monster fish with an insatiable appetite just gets too big and too hungry for a beginner to handle. We recommend a 180-gallon tank for these beautiful fish and a weight on top of the lid. In nature they are known to jump up to tree branches for monkeys!

Whether you’re a beginner or advanced aquarist, Aquatic Warehouse has all the supplies you need to keep your tank running smoothly, from aquarium controllers to filtration. Check out our website, stop by our store in Kearny Mesa, or give us a call at 858-467-9297.