suspect, on their chance of food. The limit of life and growth in
cold-blooded animals seems to depend very much on their amount of
food. The boa, alligator, shark, pike, and I suppose the trout also,
will live to a great age, and attain an enormous size, give them but
range enough; and the only cause why there are trout of ten pounds
and more in the Thames lashers, while one of four pounds is rare
here, is simply that the Thames fish has more to eat. Here, were the
fish not sufficiently thinned out every year by anglers, they would
soon become large-headed, brown, and flabby, and cease to grow. Many
a good stream has been spoilt in this way, when a squire has unwisely
preferred quantity to quality of fish.

And if it be not the quantity of feed, I know no clear reason why
chalk and limestone trout should be so much larger and better
flavoured than any others. The cause is not the greater swiftness of
the streams; for (paradoxical as it may seem to many) a trout likes
swift water no more than a pike does, except when spawning or
cleaning afterwards. At those times his blood seems to require a
very rapid oxygenation, and he goes to the 'sharps' to obtain it:
but when he is feeding and fattening, the water cannot be too still
for him. Streams which are rapid throughout never produce large
fish; and a hand-long trout transferred from his native torrent to a
still pond, will increase in size at a ten times faster rate. In
chalk streams the largest fish are found oftener in the mill-heads
than in the mill tails. It is a mistake, though a common one, to
fancy that the giant trout of the Thames lashers lie in swift water.
On the contrary, they lie in the very stillest spot of the whole
pool, which is just under the hatches. There the rush of the water
shoots over their heads, and they look up through it for every
eatable which may be swept down. At night they run down to the fan