Eileen here. Some myths and legends are universal. Almost every country has some version of a “bigfoot” legend. Nessie is one of Scotland’s biggest celebrities. People are abducted by aliens and UFO’s are spotted in the sky around the world. What does the aquarium hobby contribute to this list?
“Fish only grow to the size of their aquarium.”
Like most of those other stories, this one likely started because people saw some truth behind it. They saw their fish grow large in relation to their aquarium, stop growing, then die. But, just like we now know that the Earth is not flat and we will not fall off the edge of it if we sail too far, we now know that the size of an aquarium does not dictate the size of a healthy adult fish.
The most common victim of this theory is the comet goldfish, the fish often sold as very inexpensive feeder fish or won in carnival ping-pong ball toss games. People win the fish or buy them as inexpensive pets, not knowing that the tiny fish they took home should be able to become an 8-10 inch adult with a lifespan of 10 years or more if well cared for. “Goldfish bowls” are sold almost everywhere that carries fish supplies. Small aquariums – 10 gallons or under – are often sold with pictures of small fancy goldfish on the box so it is no wonder that people may be unaware of the problems they are walking into.
Keeping any animal, fish or otherwise, in a habitat that is too small for it causes a number of problems that might not be obvious at first. The fish people win at carnivals or purchase as small juveniles might be fine for a short time in a small aquarium, but as the fish grows, so does its requirements. Looking at the same situation in terms of a person instead of a fish, it becomes more obvious. An infant, for example, doesn’t require much space for his needs to be met. He can feed and exercise within the area of his nursery and regular cleanings can keep his nursery healthy. But, as the infant grows into a toddler, his needs also grow. He requires more space to exercise so his muscles develop properly. He is growing and needs more food and so produces more waste as a result that the same regular cleanings the infant received cannot control. As he grows through his life, that boy can certainly grow into a man if never let out of the nursery that he was kept in as an infant, but that man will not be as healthy as he could be. His hygiene and development will have suffered from being kept in a confined space and not allowed to flourish and develop properly and he will probably not live as long as a man whose environment has been allowed to grow with him.
The same happens when a fish is kept in a small tank. As the body of the fish grows, so does the amount of waste it produces and the food it needs. This can affect the water quality of the aquarium and lead to disease caused by high ammonia levels, high nitrite levels, low dissolved oxygen content, low pH and other incorrect parameters. Just as a person kept in a small space cannot grow properly, the fish would also physically not be able to grow to its full size. Its body and skeletal structure may be stunted by the lack of space and ability to exercise and swim as it should, but the internal organs often continue to grow at a normal rate. The internal damage this causes, in combination with water quality issues, will lead to a premature death.
While a small tank can certainly affect the size of the fish, it is not the way that we once believed. There is no internal sensor in a fish that can detect the size of its environment and adjust its growth accordingly. The fish we keep are just as dependent upon us as small children to give them the proper care needed to keep them healthy so it is up to us to be aware of what their needs are and to do our best to make sure those needs are met throughout the fish’s life.