“Stunted fish” is a condition whereby it is used to describe a fish which has stopped growing and the size it achieves is actually below the normal average size of a typical adult specimen. Usually stunting can happen when you malnourish your pet, stuff it in a tight living condition (small mini tank) with poor water quality or the condition can also happen due to genetic disorder as seen with defective strain.One of the most typical examples which I’ve seen occur when a fish become stunted is on Amazon discus. Normally an adult fish which are well cared for can easily grow to attain a size of one foot and above with the best living condition provided at all times. Usually one of the main culprits leading to an undersized adult discus fish is basically related to the diet whereby natural discus in the wild would normally get all the live feeds with high protein which it can find comprising mostly worms. In home aquariums whereby aquarists will usually refrain from using live feeds to avoid fouling the water and substituting with dried pellets, this will usually lead to the fish not getting a well balanced diet.
Confined space limitation as what you typically see happening in home aquariums, will also subject the fish and exposing them to the risk of becoming stunted or not growing at all. Usually overcrowding is major problem because aquarists always have the tendency to think that whatever space in the tank not filled should have gone wasted. But this is not the case because if your pet doesn’t get the room to swim freely and flex its muscles, it will never grow to attain the right size. When this happens, I would suggest you remove some of your fish to another tank or give them away for adoption or else, you risk causing the whole batch of fish getting poisoned due to heavy waste concentration in the water or as described above, they will also ended up becoming stunted.
Stunted growth also has negative implications towards the health of the fish. There are reports that claim that despite the overall size of the fish not getting bigger, the organs will actually still continue to grow and enlarge. Personally, I’m not sure how true this statement is because basically some of the discus fish which I had that become stunted actually still remains fertile to produce the next generation of fry that can grow normally to an adult size. Strange, but this is true based on my observation. However, in certain species like the guppy, stunted fish often do not live long and as an enthusiast, it will be very depressing having a pet which did not grow to a large adult size and it will soon suppress your interest towards the hobby.
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