1. The pond and river fish begin to reproduce usually when five months old. They all produce their ova at the beginning of summer. Like the marine fish, the females of these kinds never emit all their ova, nor the males all their semen, at once; but both sexes are always found to contain a portion of the reproductive substance; they produce their ova at the proper season. The cyprinus five or six times a-year, and especially under the influence of the stars. The chalcis reproduces three times, all the rest but once a-year.
2. They deposit their ova in the stagnant parts of rivers and ponds among the reeds, as the phoxinus and perca. The glanis and the perca produce their ova in strings, like the frog. That which the perca produces is so involved that, on account of its breadth, the fishermen collect it together from among the reeds in ponds. The larger individuals of the glanis produce their ova in deep water, some where it is a fathom deep; but the smaller ones in shallow water, and especially at the root of the willow or some other tree, and among the reeds and mosses.
3. The fish fold themselves together, sometimes a large one with a small one, and approximate the passages, which some call their navel, from which they eject their respective seminal matter, the females their ova, and the males their spermatic fluid. Those ova with which the semen of the male has been mixed immediately or in the course of a day become whiter and larger, and in a short time the eyes of the fish make their appearance; for in all fish, as in other animals, this part is most conspicuous, and appears the largest. But, if the seminal fluid does not touch any of the ova, as in the case of sea-fish, these become useless and barren.
4. From the fertile ova, as the fish increase in size, something like a shell is separated; this is the membrane which envelopes the ovum and the embryo fish. As soon as the seminal fluid is mixed with the ova a glutinous matter is formed, which fastens them to the roots or other substance on which they are deposited. The male watches over the place where the greatest number of ova are deposited, and the female departs as soon as she has spawned. The development of the ovum of the glanis proceeds the most slowly, for the male remains by them for forty or fifty days, in order that they may not be devoured by fish chancing to come that way.