Fish, as you know if you read this article, breathe by taking in oxygen dissolved in water. Now, the two main ways that oxygen gets into the water are by diffusion from the air or by water turbulence. But both of these methods require a surface of liquid water. When winter comes and lakes and ponds freeze over, no more oxygen gets in. So, how do goldfish survive when there is a lack of oxygen? The answer is, they turn to alcohol!
Most animals – even fish – will quickly die if they can’t take in any oxygen but goldfish can potentially stay alive for months without it. When animals burn fuel without oxygen a substance called lactic acid is made. This is poisonous and will kill if it can’t be got rid of quickly. That’s why oxygen is essential. But goldfish have found a way around this problem. They have another way of burning fuel using a different set of proteins, unique to them. Instead of lactic acid this produces alcohol – ethanol to be exact.
Now, alcohol is a poison too so why doesn’t it kill the goldfish? Firstly, they only use this method as a last resort when there is no oxygen to burn. Secondly, it is produced in quite small quantities and so they can get it out of their system before it does too much damage. Bear in mind that the fish will spend the winter almost hibernating so they don’t need to produce much energy.
Though they don’t make very much alcohol, it would be enough to stop them driving a car. Tests have shown that they have more than 50 milligrams of alcohol in every 100 millilitres of blood – the same as the legal drink-drive limit in Scotland. So, never accept a lift from a goldfish – at least not in winter time!