Let us do a thought experiment. Suppose Jesus is not a fictional character or a religious leader who was made into a direct incarnation of God. According to Zarathustra, the first well-known monotheist, all sentient creatures are His children and because He loves His children it is forbidden to kill sentient creatures for such use of their body parts as food, leather, gelatin, enzymes use in the manufacture of most cheeses, etc. This makes sense because the Heisenberg indeterminacy proved that the laws of physics are only laws of probability (that resemble classical Newtonian mechanics at the scale much above that of individual electrons in atoms.) This means that the electron transitions in the neuro-chemical processes of consciousness are not perfectly determined; there is a measure of free will in every creature that has a conscious brain. This free will endows even fish with an intrinsic dignity that forbids killing them for food. We are assuming that Jesus was so connected to God that he would know this. That Jesus never studied quantum mechanics would be no excuse.
There is no such thing as a perfect scripture the author of which got some sort of free ride from God to guarantee that it is infallible, especially when language itself is so imperfect and if the missing details of Jesus life were filled in by assumptions about him that are not recorder, it is most likely that the authors just assumed that this perfect incarnation of God conformed to such practices as eating fish because the possibility that fish suffer never occurred to them