Pliny the Elder [1st century CE] (Natural History, Book 9, 32): It is also a fact of nature that different fishes hold the first rank in different places. ... the salpa in the neighborhood of Iviza, though elsewhere it is a disgusting fish, and everywhere it is unable to be cooked thoroughly unless it has been beaten with a rod... - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.79): Salpa, as Pliny says, is an repulsive and cheap fish. Contrary to nature is this wonder, that it can never be boiled unless it is first strongly beaten with a club or a rod. This fish signifies certain sinners and sordid lives, who can never be boiled by the fire of the Holy Spirit or of charity, so that they may be the chosen food of the divine will, unless they are first punished by some salutary scourge of infirmity or tribulation.. - [Badke translation/paraphrase]