Sources : Aphorus

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:40): The aphorus is a small fish that cannot be caught on a hook due to its smallness. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.13): Aphorus is a small fish, as Isidore says, which cannot be caught with a hook because of its smallness. Blessed, therefore, and truly blessed is lowly humility and small humility, which neither the inveterate malice of gluttony can deceive nor the enemies of the human race ensnare with their snares. For humility knows no chance. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.26): And ther be some fish so small, yt unneth they be taken with hooks, as Isi[dore] saith, li. 12. Asforus is a litle fish, & for litlenesse it may not be taken with hooks... - [Batman]