Sources : Astaraz

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.4): Astaraz is a fish, as Aristotle says, which is born in autumn and at the beginning of spring. For in the foam of the rain near the banks, when it has condensed, fish of this kind are seen to boil up, just as beetle worms boil up in horse dung in summer. But others said that it is generated from the silt of the earth and is nourished from the silt of the rain. When the weather is cold, they cannot be easily caught, since they are hidden in holes and hollows; and if the day is clear, they come up to the land on the banks to seek warmth. But the brightness of the sun is very contrary and harmful to them, and therefore they seek the shade of trees under which they can be protected from the sun. But when the year has had much rain and is hot, an abundance of this species is found. - [Badke translation/paraphrase]