Sources : Tuna
Pliny the Elder [1st century CE] (Natural History, Book 9, 20): But no creature harmful to fish enters the Habusoj Black Sea besides seals and small dolphins. The tunny enter it by the right bank and go out of it by the left; this is believed to occur because they can see better with the right eye, being by nature dim of sight in both eyes. ... In winter they do not wander; wherever winter catches them, there they hibernate till the equinox. They are also frequently seen from the stern of vessels proceeding under sail, accompanying them in a remarkably charming manner for periods of several hours and for a distance of some miles, not being scared even by having a harpoon repeatedly thrown at them. Some people give the name of pilot-fish to the tunny that do this. ... The season for catching tunny is from the rise of the Pleiades to the setting of Arcturus; during the rest of the winter time they lurk at the bottom of the water unless tempted out by a mild spell or at full moon. They get fat even to the point of bursting. The tunny's longest life is two years. - [Rackham translation]
Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 12.13): There are many tuna in Pontus. They spawn the most there, for nowhere else do they grow to full size more quickly. This certainly is due to the sweet waters. The tuna come in springtime; they enter via the right-hand shore and leave by the left. It is believed this happens because the tuna see more acutely with their right eyes than with their left ones. - [Arwen Apps translation, 2011]
Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:14): The tuna [thynnus] has a Greek name. They come in the spring. They approach on the right and depart on the left; hence it is believed that they see more acutely with the right eye than with the left. - [Barney, Lewis, et. al. translation]
Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.49, 6.50): [Thomas describes the tuna under the names tygnus, tygnus pontho and tunnus.] [Marine monsters 6.49] Tygnus is a sea monster, as Solinus says. It has a tail two cubits wide. It grows in the sea and never elsewhere. It goes out to the land to graze. They enter on the right bank, they leave on the left; and this is supposed to happen because they see more with the right eye, but are dull with both eyes. When the wind is blowing from the north, they are more willing to leave. Pliny: They pursue ships out of curiosity to see the sails driven by the wind; and they are affected by this astonishment to such an extent that they are not moved by terror when tridents are thrown upon them. In the winter season they are hidden under the water. They grow fat enough to live a long life for three years. In Ethiopia there are wild beasts, which are of a brown color, and have twin udders on their breast, who suckle their young, as Solinus says. [Actually from Pliny the Elder, Book 8, 30: "Ethiopia produces lynxes [lyneas] in great numbers, and sphinxes [sphingas] with brown hair and a pair of udders on the breast, and many other monstrosities". Thomas appears to have included this sentence in error.] [Marine monsters 6.50] Tygnus of the Pontus, as Solinus says, does not give birth elsewhere, and this because of the sweeter waters. It enters the river on the right side, and exits on the left. This is believed to be because it sees more sharply with the right eye than with the left. [Marine monsters 6.51] Tunnus ia a sea fish. Dissolve its eyes or its lungs in a glass bottle with sea water, and whatever you write with it will shine like a flame in the night. - [Badke translation/paraphrase]