5. A few eels in some places are fed upon mud, and any kind of food which may be cast into the water, but generally they live upon fresh water, and those who rear eels take care that the water which flows off and on upon the shallows in which they live may be clear, where they make the eel preserves. For they are soon suffocated if the water is not clean, their gills being very small. For this reason those who seek for them disturb the water. In the Strymon they are taken about the time of the rising of the Pleiades. For the water is disturbed at this season by the mud which is stirred up by contrary winds, otherwise it is useless to attempt to obtain them. When dead, eels do not rise and float on the surface, like other fishes, for their stomach is small; a few of them are fat, but this is not usually the case. 6. When taken out of the water, they will live five or six days; if the wind is in the north they will live longer than if it is in the south. If they are removed from the ponds to the eel preserves during the summer they perish, but not if removed in the winter; neither will they bear violent changes, for if they are taken and plunged into cold water, they often perish in great numbers. They are suffocated also if kept in a small quantity of water. This takes place also in other fish, which are suffocated if kept in a small quantity of water which is never changed, like animals which breathe air when enclosed in a small quantity of air. Some eels live seven or eight years. Fresh-water fish make use of food, and devour each other, as well as plants and roots, or anything else that they can find in the mud; they generally feed in the night, and during the day dwell in deep holes. This is the nature of the food of fish. CHAPTER V. 1. All birds with crooked claws are carnivorous, nor are they able to eat corn even when put in their mouths. All the eagles belong to this class and the kites, and both the hawks, the pigeon hawk namely, and the sparrow hawk. These differ in size from each other, and so does the triorches. This bird is as large as the kite, and is visible at all seasons of the year; the osprey and vulture also belong to this class. The osprey is as large as the eagle, and ash-coloured. There are two kinds of vultures, one small and whitish, the other large and cinereous. 2. Some of the night birds also have crooked claws, as the nycticorax, owl, and bryas. The bryas resembles an owl in appearance, but it is as large as an eagle; the eleos, ægolius, and scops also belong to this class. The eleos is larger than a domestic fowl, the ægolius is about the size of that bird, they both hunt the jay. The scops is less than the owl; all three of these are similar in form, and carnivorous. Some that have not crooked claws are carnivorous, as the swallow.