My favourite fish [yes, I have a favourite fish] is superbly camouflaged against the pebbles and stones in mottled browns and flecks of grey.

As my eyes become accustomed to this underwater world, life shows itself. First a grey flick of a tail and a freshwater shrimp dashes into a patch of weed, disturbing a torpedo shaped aquatic beetle, which whizzed downstream past my leg. More subtle movements, almost imperceptible at first, but definite motion - the stones are moving.... These are the temporary homes, constructed by caddis fly larvae, whose fleshy bodies needs protection from predators; each grain of sand or miniscule pebble glued together by the incumbent, creating a tube-shaped tunnel to live in, before the larvae metamorphoses into an adult fly, out on the water's edge. 

My fish lay motionless on the stream bed stones, its diminutive size an advantage whilst trying to stay hidden. But there, no more than a wading foot in front of me was the bullhead. At no more than 10cm long, its large rounded head, accentuated on its slender flattened body gives rise to its name. The alternative name of 'miller's thumb' derives from the fact that in times gone by, the local miller was said to get a distorted and enlarged digit from years of rubbing the grain between the thumb and forefinger, resembling my little fish's head.

Small in size and a tasty morsel for many a predator, from kingfisher to otter, the bullhead has adapted to fight back. Spiny fins on its back and sides often make it a painful meal and its art of hiding in plain site also serve it well.

In springtime, eggs are stuck on the underside of large stones by the female, whilst the male guards over them, fanning the water to increase the oxygen, attentive until they hatch. Miniature versions of their parents, the young hide out, seeking refuge in the shallows and feeding on aquatic invertebrates like the freshwater shrimp encountered earlier in this watery world. My time in the stream now over, as I reacquaint myself with one of our smaller freshwater fish, I decide to retire to the bank, while life continues flowing by for the miller's thumb.