Selecting the Right Fish In An Aquarium

Selecting the Right Fish In An Aquarium

How many times have we brought the wrong fish to the Aquarium? How many times did we face this disappointment of having the fish outgrown the tank? Lastly, the pain to bear 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 faced this situation as an aquarist then this article is for you. Also, request the readers to share this article with beginners to the fish hobby.

I get this query 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 feet 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 feet tank. I had the Aligator Ghar. When it was small it looked beautiful. Imagine, I had 6.2 feet in length tank with a depth of 1 foot and a height of 2 feet. (6.2ft x 1ftx2ft) but I had a problem with the alligator Ghar getting deformed. The mistake I had done was providing him 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 to bring home and why?

It’s easy to be excited when individual steps 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 fish.

Let’s look at the popular fish that a beginner should avoid for lack of space.

Stressed Arowana in small tank
Stressed Arowana in small tank

Silver Arowana: Minimum space of 5 ft length x 20 inches depth x 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, and insects to birds accidentally droppings from the nest. 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 feet to 12 feet long. It is a difficult fish to start within a residential aquarium. Arowana is very sensitive to nitrites. 40% to 50% Weekly Water changes are necessary to keep the nitrites low. Water temperature should bne between 22° celsius to 28° celsius.

Oscar fish: The sheer beauty of the Oscars can compel any beginner to go for this fish. These fish comes in various colors from copper, and albino with beautiful orange made on them to tiger Oscar, etc. They are omnivorous and belong to the 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 feet. The tank needs to be at least a height of 2 feet. They look cute when they are small at a size of 2 inches. But the problem starts when they start growing very fast. Most of the pattern on the body fades away. They are vicious eaters. Malnourishment as well as obesity is also a problem with Oscar. They cannot be housed with other fish which do not fall into the monster fish category. I know of people who have parrotfish in 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 kind, as it becomes very territorial due to lack of space. They like to dominate their kind. Old ones will give their dominant position to young Oscar. Oscars grow upto 12inches. The temperature of the water is between 24° celsius to 28° Celsius. In Short, every addition of Oscar needs roughly 110 liters. Give them good filtration and a good diet. Even if they are omnivorous they prefer live fish, worms, and insects.

Iridescent Shark catfish
Iridescent Shark catfish – Not recommended

Iridescent Shark catfish: Beginner fish hobbyists 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 3ft tank within 6-8 months. It normally grows to around 50 inches. 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? A gullible hobbyist who doesn’t research well before buying this fish regret later 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 feet tanks in length x 18inch depth x 2 feet in 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 giving it or putting them into a pond or a well. They are hardy fish and can tolerate harsh water conditions. The water temperature should be 22° celsius to 27° celsius.

Avoid this monstor fish – Redtail Catfish

Redtail catfish: This fish is not for beginners and is 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 driftwood, and 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 feet in captivity and up to 5ft in length in wild. This fish looks very attractive due to its caudal red tail. It can be very aggressive. You cannot blame them due to their predatory nature. To house this fish you will require a minimum 5ft 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° Celsius to 27° Celsius.

Giant Gourami - A Wrong fish for a small Aquarium
Giant Gourami – Do you really want it?

Giant Gourami: A gentle giant that can grow upto 20inches long. So a tank of around 5 feet with a depth of 2 feet and a height of 3ft 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 kind as they like to be dominant. As adults, maturity and calmness sink into their behavior. 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 tend to jump out. They are herbivorous fish and also have a personality of their own. They recognize their owner’s 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° Celsius to 30° Celsius is needed by this fish to grow well.

Common Pleco - Can grow huge.
Common Pleco – Can grow huge.

Common Pleco:- 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 to 2 feet. These are sold in the shop as 2 inches but outgrow the tank in a few years. House them if you can give them a bigger space to live in around 4 feet tank with 1.5 feet in depth and at least 2 feet 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 inches in length. Looking after the pleco is a lifetime commitment. There are various plecos in the trade nowadays. Do well your research and house them. And always provide them with driftwood as it provides them with fiber requirements. 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 they are most active.

Butterfly koi fish
Butterfly koi fish

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

Puffer fish with teeth
Puffer with Teeth. Keep only if you can provide Diet

Pufferfish:- They look very tempting to the eye. Many hobbyists make the mistake of getting it and having it in a community tank. Some species can grow large and they can eat the other small fish in the tank. If they find there are larger fish, the possibility is that they will bite their fins. They are carnivorous. They eat snails, shellfish, and other fish. This fish is strictly a big no in the community fish and is not meant for a beginner. Many fish species have teeth and do not stop growing. You need to give them hard shells to bite in doing so this trims their teeth. If not given their diet they may starve themselves eventually leading to death. It is challenging to feed puffer fish. Leftover food can cause nitrite and nitrate spikes in an Aquarium. Large puffers require around 350 liters tank. Small puffers require around 150 liters. Utmost care should be taken regarding their diet. They can be very messy too. The required Temperature is between 22°celsius to 28° Celsius.

Aligator Gar not meant for home
Aligator Gar – Fish for the experts

Aligator Gar :- Avoid this fish if you cannot provide a minimum 6-foot tank. This fish is carnivorous. It grows fast in length. This fish should never be kept at home. The fish can be deformed if the space becomes too small and it cannot turn. I had a friend who kept this fish and it became deformed as the depth of the tank was too less to swim properly. The minimum depth of the tank should be at least 3 feet. It requires ample space to swim. It diet consists of mainly live fish and also eats shrimps. The temperature requirement is 24-degree celsius – 28 degree celsius

Bala Shark
Bala Shark – The most active fish in an Aquarium

Schooling fish: Other schooling fish need at least 1000 liters. Tinfoil barbs and Bala sharks can grow up to 1 foot. They are swift swimmers and require large aquariums. Smaller aquariums can damage their fins. Even the silver dollar can grow large. These are all schooling fish and should be kept 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.

Some fish in Cichlid variety can grow big – African Cichlids, Flowerhorn, Oscars and parrot fish. These are not suitable for tanks below 3 feet. If possible and advisable is to go for a bigger tank size if the space permits.

What to do if your fish has overgrown your tank?:

  • Approach your aquarium shop and request them to take the fish in exchange for other fish. Sometimes, they do take the fish and help you out.

  • Approach, people who keep large fish in a large tank. But do check the compatibility of their existing fish.

We are familiar with the phrases “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? Will this cutie grow to be a monster? Am I providing them with good space to grow? Or am I bringing a monster only to get rid of later? Be prepared when you step into an Aquarium shop. Don’t fall prey to what the seller is doing. Do your research on fish with tank space in mind. And remember Aquafishcare has just warned you not to get a monster.


  • Fish should be kept in a tank and not in a bowl, not even a Goldfish.

  • Please do not release monsters or any type of fish in open water bodies – lakes, rivers, etc. Quite often they might attack the native species and be a threat to their existence.

  • Do research the fish growth pattern. Check the tank size for that species. Usually per fish is one gallon. But then it becomes debatable as the fish grow the 1 gallon rule changes considerably.

  • Do your homework. Its better to take precaution then to be sorry.

Watch the Video of the Monster Fish Tank

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