Salt streams, like the Aji Su, are equally unproductive, and the fresh-water rivers of the plateau fall so low in summer that fish cannot become numerous in them.

Thus it is only in Zagros, in Azerbijan, and in the Elburz, that the streams furnish any considerable quantity.

The kinds most common are barbel, carp, dace, bleak, and gudgeon.

In a comparatively few streams, more especially those of Zagros, trout are found, which are handsome and of excellent quality.

The river of Isfahan produces a kind of crayfish, which is taken in the bushes along its banks, and is very delicate eating.
It is remarkable that fish are caught not only in the open streams of Media, but also in the _kanats_ or underground conduits, from which the light of day is very nearly excluded.