Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.24): Carpo or carpera, as he says [i.e. Liber rerum], is said to have its name from this: for one can say carpera as if 'a carp gives birth' [carpens parit, an obscure reference]. It is a fish of broad ponds or rivers, with golden scales. This fish, with her eggs in her belly suitable for spawning as nature dictates, goes to the male fish and gives a light pulse with her mouth to encourage spawning. Then the male, understanding that movement, emits milk instead of seed. The female, receiving the ejaculate with her mouth, immediately lays eggs for offspring. For a female cannot lay eggs unless she has first received the seed with her mouth. Receiving the seed seems to help not so much for childbirth, but for the conception and formation of the eggs, from which offspring are hoped for in the coming year. Sometimes in the first year after its birth a black worm is born near the ear, and this often after August; and by this corruption it dies; its remedy is fresh and river water. It produces offspring in few waters. The opinion of the common people is that if a small pit nine or ten cubits in length is newly made, and they are placed in each pit individually with their equals, that is, a male and a female, their offspring will come forth. And it should be noted that they are not to be picked to put into the pits until immediately before the birth. But after they have given birth, they are taken out. But the young, when they are three or four months old, are cast out and stored in the pit, where they have to grow up until they are perfect. The brain of the carp is said to wax and wane according to the waxing or waning of the Moon; and although this is the case with all fish, yet more so with carps, as some have said of the wolf and the dog among the quadrupeds. The carp fish has many tricks to avoid being caught in the net. For when it has entered the net, it looks for the opening; and if it does not find it, it tries to jump into the free air above the net, so as to fall outside. But if it cannot, it looks for a way under the net; and being frustrated in this, it holds onto the grass with its mouth at the bottom of the water, so that the net comes up empty. If it does at any time succeed, as the last attempt does this: coming from above with a rush into the mud it lowers its head more strongly below the net, so that, of course, passing below the net through the mud with the force of its tail, it escapes by a trick. There are five ways, then, in which the cunning fish tries to escape. This signifies the fivefold cunning of malicious men, by which they certainly look to subterfuge, lest they should be caught in the nets of the divine word. We leave the exposition of these to the learned reader. - [Badke translation/paraphrase]

Vincent de Beauvais [circa 1190-1264 CE] (Speculum naturale, Book 17.24): The carp is a fish with golden scales in lakes or rivers, so called, as if it were carpens [Latin "plucking"], for when it has eggs in its belly, as nature dictates, suitable for spawning, it approaches its male and signals with a light stroke of its mouth to help the spawning, then he emits milk instead of semen, which she receives with her mouth; she immediately lays eggs that will benefit the offspring. For it cannot lay eggs unless it has first received semen in its mouth. But when semen has been received, it seems to help not only with the birth, but also with the conception and formation of eggs, from which offspring are expected in the coming year. The seeds sometimes produce a black worm in the first year of birth, but after its own growth it grows and this often dies of disease after the eighth month and dies of disease. The remedy is fresh and river water, whose offspring are produced in a few waters, if in each of the ten-cubit-wide newly made ditches they are placed individually with their peers just before birth. The popular opinion is that their offspring are produced in this way. But after they have given birth they are taken out. The offspring, too, after three or four months have strengthened, are thrown back into the ditches and placed back where they have time to grow with the perfect ones. This fish has many tricks to avoid being caught in the net, for when it enters the net, it goes around looking for an opening, which if it does not find, it tries to jump into the free air above the net, so that it falls out. Sometimes it seeks refuge under the net. Sometimes it holds a piece of grass in its mouth at the bottom of the water, so that the net is swallowed up when it comes over. Sometimes, too, coming from above, it fastens its head more strongly in the mud with an attack, so that the net passing through its tail may be frustrated by its capture. Its brain is said to increase or decrease according to the increase and decrease of the moon. And although this is the case in every fish, yet in this one it is more so, as among quadrupeds, in the wolf and the dog. - [Badke translation/paraphrase]