Worst Fish to Start a Fresh Water Tank

We will cover the worst fish to start a freshwater tank with and cover the reasoning behind the advice. We have made these judgements based upon the difficulty level needed to maintain an aquarium based on the characteristics of the fish and above average maintenance needed to care for the tank and their occupants.

New fish tank owners have so many options to choose from when starting their first tank. It can be overwhelming, and many find the pet store options to be beautiful but lacks the guidance needed to avoid the pitfalls of owning fish they are not prepared to support.

In general, the worst fish for the beginner are ones the owner is not prepared to care for. High waste producing fish require more tank maintenance while aggressive or territorial fish may starve or kill other fish and less hardy species cannot adapt to minor environment changes or neglect which can be a challenge for beginner aquarist.

Many new owners don’t realize the small fish they purchase from the pet store may easily outgrow their tank or realize too late that some fish species need more schooling companions than their tank size can accommodate. Learn more about how many fish are safe for your size of tank in the article How Many Fish Can I Have in an Aquarium.

From the reasons above and more, we have compiled a list of fish that are the worst for beginners to start a new tank with. As you search the web you will find lists that are different than ours and that is ok. The common ground is the reasons the fish are the worst to start a freshwater tank with.

Let’s cover the most popular fish and work our way down.

  1. Red-tailed Black Shark

The red-tailed black shark, also known as the redtail shark and redtail shark minnow, is a species of freshwater fish in the carp family. While the red tail sharks can be very aggressive to tank mates, they rarely bite or do any damage to the other fish. But it will chase some fish relentlessly and prevent them from feeding.

  1. Goldfish

 A single-species aquarium is preferred since they will try to eat any animals (and plants) that fit in their mouths. Goldfish are very resilient with fluctuations in water quality. Goldfish produce a lot of waste and toxic ammonia requiring lots of water changes to keep their tank clean.

Common goldfish (Carassius auratus) grow to about 12 to 14 inches, so they require 30 gallons of water per fish (or two goldfish in a 55-gallon aquarium)

  1. Pleco Fish

Countless times, people have asked a store employee which fish they recommend that will eat the algae taking over their tank. The usual response is to show a tank full of small one-to-two-inch common plecos. While indeed these fish will nibble on the algae, they will grow to become enormous waste producing machines.

The common pleco can grow to eighteen inches long and should be housed in nothing less than a ninety-gallon tank as an adult. They really are one of the most unsuitable fish for the common aquarium. It is much easier for the beginner to clean whatever algae is on the glass manually than deal with these truly monstrous and not so attractive mature fish.

  1. Bichirs

These fish are interesting in that they can survive for short periods out of the water due to their ‘lung like’ swim bladder. The problem with Bichirs is that they will eat any other fish that they can get into their mouths. Reaching adult sizes of one to two feet, they can fit quite a lot in their mouths! They are also notorious jumpers.

  1. Black Molly

Well, it has a peaceful nature. It would be a great choice if you plan to come up with a community tank having many other fish types. The fish is often liked because it will easily adapt to the freshwater aquariums without much of an effort. You can easily transfer it from one tank to the other and it will still be comfortable.

Mollies like brackish water which is a mixture of fresh and saltwater. So while they do well in freshwater, they do even better in brackish water. This is okay if you want to keep a brackish tank. They are also live breeders, they can reproduce rapidly, leading to potential overpopulation issues if not managed correctly. Some livebearers can also be susceptible to diseases. Just make sure to get them to a separate tank as the parents tend to eat the young ones.

  1. Bala Shark

This fish is not a shark at all but receives its name from its triangular dorsal fin. The bala shark is a peaceful, hardy fish but it will grow too large for the beginner’s first tank (up to 10 inches when reaching adult size). Many novice aquarium hobbyists make the mistake of buying these fish because they are sold as juveniles when they are still small – it won’t be long, however, until they outgrow your tank!

  1. Discus Fish

Discus are generally calm, peaceful fish, but as cichlids, they can be aggressive toward one another, especially when attempting to pair off and spawn. Discus grow to be quite large and require an aquarium of 75 gallons or larger for a breeding pair when full grown. Tall aquariums are best to accommodate their body shape.

Discus prefer warm, soft, acidic water.  pH should be between 6.0 and 7.0, with hardness between 1° and 4° dKH (18 to 70 ppm). The temperature should be kept between 82° and 86° F. When purchasing discus, always ask about the water chemistry they were raised in. Discus require pristine water quality, and weekly water changes of 10% to 25%.

  1. Oscars

Oscars are large, aggressive, and messy fish that require a spacious tank. They are not suitable for smaller or community tanks and can be difficult to care for properly.

  1. African Cichlids

African cichlids can be territorial and aggressive, making them challenging for beginners to keep in a peaceful community tank. Additionally, they may have specific water parameter requirements depending on their species.

  1. Flowerhorn Cichlids

Flowerhorns are known for their striking appearance, but they can be aggressive and require a tank of a suitable size. They also have specific dietary needs that might not be easy for beginners to meet.

  1. Arowanas

These large, predatory fish require very large tanks and can be expensive to care for properly. They are not recommended for beginners due to their size and dietary needs.

  1. Archerfish

Archerfish have unique hunting behaviors and may require live prey, making them more challenging to feed compared to standard fish foods.

  1. Electric Catfish

These catfish are not recommended for beginners due to their specialized care requirements, such as the need for soft water and a diet that includes live or frozen foods. The electric catfish are known for producing an electric shock when they are stressed or feel threatened.

  1. Pufferfish

While pufferfish can be cute and fascinating to watch, they have specific dietary and water parameter requirements that can be challenging for beginners to maintain. This is a high maintenance fish.

  1. Freshwater Stingray

Stingrays are large and require a lot of swimming space. They also need soft, acidic water and a specific diet. These factors make them unsuitable for beginner aquarists.

  1. Redtail Catfish

Redtail catfish grow quickly and can reach very large sizes, making them unsuitable for most home aquariums. They also require high quality and high-volume filtration and a specialized diet.


It’s crucial to research and select fish species that are appropriate for your tank size, water parameters, and your level of experience as an aquarium hobbyist. Before adding any fish to your freshwater tank, make sure you understand the species’ requirements and have the necessary equipment and knowledge to provide them with a healthy and suitable environment.

If you are new to the hobby, consider starting with hardier and more beginner-friendly fish species to gain experience before attempting to care for more challenging species. Remember, the worst fish to start a fish tank with are the ones you are not prepared to care for.

If you are a beginner, be sure to also read Best Fish to Start a Freshwater Tank and Best Fish to Start a Saltwater Tank.

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