Looking below the surface

A remarkable thing about the fish in our man-made canals is that they are there at all. They are a testament to nature's ability to find a way. Even in between bricks, mortar, metals and timbers where the protected bullhead may lurk. In the bad old days of polluted and neglected post-World War II waterways, some canals and rivers were virtually devoid of life and fish stocks declined. However, since then, our charity has helped canals become cleaner and greener, and they've made a remarkable recovery.

Today, fish are right at the heart of our canal ecosystems. They thrive wherever waterside vegetation gives them somewhere to feed, breed and shelter. They're also vital sources of food for many species higher up the food chain, like kingfishers, herons and otters.

Wherever you find fish, it shows the water quality is good. Not because they themselves improve the water but because the plant life fish depend on does the cleaning work. Healthy fish stocks simply show what a great job the vegetation is doing.

If you take a look into the water of your local canal, here are just some of the species you might find below the surface.

You'll find plenty of roach, rudd, gudgeon and perch (above) on our canals. Roach, a member of the carp family, and rudd are difficult to distinguish to anything other than the expert eye, as they are both silvery fish, with reddish-brown fins. Perch are easy to spot thanks to a very sharp and spikey dorsal fin and pointed gill covers. Take care if handling them. Gudgeon are hardy little fish. Many an angling career has been started or saved by the capture of one or two of these small but hard fighting fish.

Many different species of carp, not least the odd goldfish, a different species, find their way into our canals. They range in size enormously from tiddlers to anything between 20 and 45lb for the bigger specimens. As greedy guzzlers who will eat almost anything, the only limit on their size is age and how much food they can find. Common carp can grow up to almost a metre in length and live for between 25 and 50 years. They aren't actually native to the UK but were introduced in the early Middle Ages (circa 1300) as food for fasting Christians.

The predatory pike has razor-sharp teeth that it uses to prey on smaller fish, but their keen eyesight is the real key to their success. Although they are found in all of our canals, rivers and reservoirs, they prefer clear waters with good lines of sight and plenty of weeds to hide in.

Tiny sticklebacks are one of the most common fish found in our canals and are a wonderful find for any small child dipping their net into the water for the first time. A much rarer find is the nocturnal bullhead, which are often only uncovered lying in the bottom of our locks during renovations. They have extra legal protection. They like the lock environment as they lay their yellow eggs among small nests of stones and masonry that have fallen to the floor.

Critically endangered eels are a species we need to conserve on the canals of England and Wales, especially because they've taken three years to get here, swimming from their birth place in the Sargasso Sea, in the western Atlantic Ocean. They arrive as tiny transparent elvers before maturing in our darkest, siltiest and muddiest canals and rivers. But they are found in any body of water because, amazingly, they are reputed to crawl over flooded land to access pools, ponds or ditches. The most mature silver eels later head back to the Sargasso Sea to spawn.

A more sinister visitor from other shores is the zander. Introduced illegally, this is an invasive species that loves to hunt in murky water churned up by boats but devastates native fish numbers. In contrast to our native fish which have to be returned to the water, it is actually illegal to return zander to our canals and rivers.

One fish we hope you'll see more of in coming years is the twaite shad, a species we're trying to help through our Unlocking the Severn project. The species is so rare it's a European Protected Species. So, with your support, we're creating fish passes to help more twaite shad and other fish reach their former spawning grounds in Mid-Wales.

From small fry to big beasts, rare finds to the everyday, and native species to unwelcome invaders, there's a lot more going on under the surface than you might imagine.