Avoid these Fish in an Aquarium

How many times have we brought a wrong fish in the Aquarium? How many times did we face this disappointment of having the fish outgrown the tank? Lastly, the pain of giving away the pet to the aquarium store for “FREE” or exchange.  How many of us were not guided by the Aquarium store? If you have faced this situation as an aquarist, then read this article.

I get these types of queries quite often “What should I do with the fish that I brought a year back? It’s grown and now it cannot even move properly in my 3 ft tank. It looks stressed. Its body shape has changed due to the shape of the tank. I had this same problem in my 6.2 ft tank. I had the Aligator gar. When it was small it looked beautiful. Imagine, I had 6.2 ft in length tank with a depth of 1 foot and a height of 2 ft (6.2ft × 1ft × 2ft), but I had a problem with the Alligator gar getting deformed. The mistake I had made was providing him with less depth to turn and move around. It was not about the length or the height. I felt sorry for it and sadly, I had to give it away.” That experience has made me write this article for all beginners or hobbyists looking to purchase these magnificent monsters for home aquaria. Truly, ‘size matters’ when deciding which species of fish to bring home and why?

It’s easy to be excited when an individual step into an aquarium shop. Some shopkeepers have good collections of monster fish. What most of them don’t tell you is the maintenance part of these species and most importantly the growth pattern of these aquarium fish.  Let’s look at the fish which a beginner ‘aquarium pet owner’ should avoid for lack of space.


Yes, you heard it right. Avoid this fish if you cannot give it a minimum space of 5 ft length × 20 in-depth × 2 ft height. Asian Arowana (Silver Arowana), grows in length very fast. It requires good feed to maintain healthy scales, fins and body.

In wild, they eat anything from fish, insects to birds accidentally dropping into the water from their nests. Good filtration is a must for this species. Arowana is a carnivorous fish. The fish when stressed has got a tendency to jump out of the tank. So, be careful not to have an open tank. Also, while cleaning the tank proper procedure needs to be followed, so as not to stress the fish.

The tank should be properly closed from the top. The growth of an Arowana is anything between 6 ft and 12 ft long. It is a difficult fish to start within a residential aquarium. Arowana are very sensitive to nitrites. 40% to 50% weekly water change is necessary to keep the nitrites low. Water temperature should be between 22°C and 28°C.

Oscar fish: The sheer beauty of the Oscar’s can compel any beginner to go for this fish. These fish come in various colours from copper, albino with beautiful orange marked on them to Tiger Oscar, etc. They are omnivorous and belong to monster category. Many hobbyists do not understand the possibility of the growth pattern of this fish. This fish is not for a tank having an aquarium length below 4 ft. The tank needs to be at least a height of 2 ft. They look cute when they are small in a size of 2 in. But the problem starts when they start growing very fast. Most of the patterns on the body fade away. They are ferocious eaters. Malnourishment as well as obesity is also a problem with Oscar. They cannot be housed with other fish which do not fall into monster fish category. I know of people who have parrot fish into their tanks with Oscars and complain of incompatibility. The fish can outgrow an aquarium very fast. It is natural for an Oscar to be aggressive and behave erratically towards other species sometimes to its own kind, as it becomes very territorial due to the lack of space. They like to dominate their own kind. Old ones will give their dominant position to young Oscar. Oscars grow up to 12 in. The temperature of the water is between 24°C and 28°C. In short, every addition of Oscar needs roughly 110 litres. Give them good filtration and a good diet. Even if they are omnivorous they prefer more live fish, worms and insects.

Iridescent shark catfish: Beginner fish hobbyist fall for this fish very easily. They are very cute and fast movers in the tank. They don’t remain cute any longer as they start to outgrow the 3 ft tank within 8–10 month. It normally grows to around 50 in. I have personally kept these fish and found them very aggressive eaters and grow very fast. These fish are also edible. Meaning they are also eaten by human beings. So, why buy these fish for an aquarium. Gullible hobbyist who don’t research well before buying this fish regret later for adding it to their tank. They are peaceful in temperament, but require lots of space. They like to swim around very fast and may hurt themselves and get stressed in a small aquarium. The minimum space should be 5 ft tanks in length × 18 in depth × 2 ft height. They are omnivorous when young, but when they become adults they turn out to be herbivorous. As a caretaker, you will need to change their diet. They will eat anything that fits in their mouth. It’s best to avoid this fish as you will regret later giving or putting them into a pond or a well. They are hardy fish and can tolerate harsh water conditions. Water temperature should be 22°C to 27°C.

Redtail catfish: This fish is not for beginners and meant only for the experts. This fish will outgrow any fish tank in less time. This fish is omnivorous, anything and everything is eaten by this tank. They can nibble on driftwoods, gravel and eat other fish too. They are confident fish and do not need any place to hide. It is recommended to feed them cut up meat, insects, shrimps and worms. This fish can grow to 3–4 ft in captivity and up to 5 ft in length in wild. This fish looks very attractive due to caudal red tail. It can be very aggressive. You cannot blame them due to their predatory nature. To house this fish, you will require minimum 5 ft tank. Even that might not be enough as it can grow much bigger. You don’t want the fish to be unhappy in a cramped small tank. Avoid this fish for lack of space and dietary requirements. Water temperature should be around 22°C to 27°C.

Giant Gourami:

A gentle giant that can grow up to 20 in long. So, a tank of around 5 ft in length with a depth of 2 ft and a height of 3 ft will do well for this species.

The height of the tank is very important for this species as they come up to breathe quite often. Having a lid on top of the tank is vital. As a juvenile, these fish are aggressive towards their own kind as they like to be dominant. As adults, maturity and calmness sink into their behaviour.

Try to avoid two male adults as they can become very territorial. Unless you can provide them with bigger tanks, avoid these gentle creatures as they also have a tendency to jump out of the tank. They are herbivorous fish and also have a personality of their own.

They recognise their owners’ bond with them very well. They prefer some live food to maintain a balanced diet. Regular water change is necessary for this fish. It is prone to common aquarium diseases. The bigger the tank the better it is for the fish to grow without stress. Water temperature of 22°C to 30°C is needed by this fish to grow well.

Common Plecos:

These are the fish commonly called “Suckers” as they are seen sticking themselves on the internal side glass of an aquarium. These fish can grow very long up to 1 foot to 2 feet.

These are sold in the shop as 2 in, but outgrow the tank in a few years. House them, if you can give them a bigger space to live in around 4 ft tank with 1.5 ft depth and at least 2 ft in height. They are good algae eaters, but may mess up as they grow into a bigger size eventually. 

There are other better algae eaters like bristle nose Plecos which normally grow to around 5–6 in in length. Looking after the Pleco is a life-time commitment. There are various Plecos in the trade nowadays. Do well your research before you house them. And always provide them with driftwood, as it provides them with the fibre requirement.

Provide them with premium Algae wafers as their main diet in an aquarium for their healthy growth. Feed them at night when the main lights in the room are put off that is the time when they are most active.


These are meant for ponds, not an aquarium. These can grow very big.  Some species grow in their tank environment. They will never grow to their full potential in a fish tank. Don’t be cruel to them. Even if you want to keep them at least 250-gallon tank is needed. More of horizontal space having a depth of 1.5 ft. They grow well within the temperature of 20°C to 26°C.

There are other schooling fish which need at least 1,000 litres. Tinfoil barbs (can grow up to 1 foot), Silver dollar, Bala sharks which can grow up to 1 foot. These are all schooling fish and should be kept in a minimum of 6-in a tank. That becomes challenging in a small tank as the fish grows. Also, check their compatibility with your existing fish in the aquarium.

We are all familiar with the phrase “Small is Cute” and “Good things come in small packages”. Is this true? Ask yourself when you step into an aquarium shop. Am I making a good decision to buy the cutie fish? Am I providing them with good space to grow? Or am I bringing a monster only to get rid off later. Be prepared when you step into an aquarium shop. Don’t fall prey to what the seller is doing. Do your own research on fish with tank space requirement in mind. And remember “Aquafishcare” has just warned you not to get a monster.

Warning: At Aquafishcare, we strongly believe that fish should be kept in a tank and not in a bowl, not even a Goldfish.

By Sunil Dcosta
Sunil Dcosta is a Proprietor. Visit www.aquafishcare.com or reach him by phone +91 9821798612.

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