As a boy keen on fishing, our favourite locations were along the Thames.

We caught many fish but rarely anything large. However, to us, size was not everything.

One fish we did tempt to our maggot baited hooks was the sprightly bright silver bleak, a rather unfortunate name for such a lively species that rarely exceeds six inches in length and swims mainly in shoals near the surface although it sometimes descends deeper.

Every so often when watching our floats our sensitive young ears would detect a strange low-pitched 'thrumming' sensation and we always knew what was about to happen.

Sure enough, about three seconds later a bleak would fling itself high out of the water in front of us.

The 'thrumming' sound was caused by pressure waves transferring from water to air created by the little fish as it swam at great speed vertically up from the depths, probably pursued by predatory perch or pike.

The fragile bright iridescent silver scales are covered in crystals of a substance called guanine.

In France, the fish were at one time exploited commercially, millions being caught.

Their scales were then washed to extract the guanine which was used to manufacture pearl essence to coastrings of artificial pearls for the fashion industry, a process invented way back in 1608 by a French chaplet.

It took about 5,000 fish to yield 100 grams of essence. The rest of the bleak was then mashed into pig fodder.

In view of this, perhaps for most of the little fish their outlook was indeed bleak.