71 % of our planet's surface is covered with water. Despite this, it is often said that we know more about outer space than we know about our oceans. There are over 25,000 species of fish described thus far, and there may be a great many more to be discovered. From the tiny gobies to the serene whale shark, fish are the most numerous form of vertebrates. Capable of living in salt or fresh water, fish are incredibly diverse, coming in all sorts of shapes and sizes. With over 40million being kept, fish are easily the most popular pet in the UK, and it would be very surprising if they ever lose this title. Fish also provide food to a large amount of creatures, including our own species.