With over 32,000 species in the world, fish can be found in the deep, dark depths of the ocean to the highest mountain rivers. After a recent visit to the largest aquarium in the world, The Georgia Aquarium in Atlanta, GA, I became fascinated by the many different species inhabiting our surrounding environment.
Among the many patterns, colour and appearances, one thing in this group of vertebrates I noticed was their eyesight. None of them appeared to have eyelids; I wanted to find out more.
Can fish sleep?
A question often asked by children (most likely owing to the apparent absence of the ability of the fish to close its eyes), I often wondered just how fish could sleep. I knew they had to, but how?
With the lack of eyelids, fish have a protective film over their eyes which stops them from having a constant force of water pushing against their cornea. Whilst asleep, most goldfish will delicately balance, perfectly still in the water, whilst other types of fish may rest in coral or balance between plants.
Most fish have colour vision, too, meaning they are able to see differences in pattern and appearance. However, most fish have a semi-blind spot right in front of their eyes, and the position of their eyes – on the side of their head – is really important. They also have really bad depth perception, so that explains why they will sometimes bump into the side of the tank or bowl!
Fish have a 3-second memory
This is a total myth; fish do have brains and within it memories which last a lot longer than 3 seconds. They will come to recognise your face and movements, and sometimes (depending on the species), even your voice!
Fish will only grow to the size of their tank
This is untrue, and so many people overstock their tank to allow for many different types of fish. The myth is that your fish will only grow as your tank allows; but this is untrue. Larger types of fish – and common goldfish in particular – will often need a whole pond, or at least a large tank, in order to live a healthy life with no problems. Never overstock your fish, the general rule is 1cm of fully-frown fish = 1 gallon in your tank capacity.