It’s a mostly harmless lie both about the other fisherman.
The lies of omission are often accomplished by being less than completely forthcoming about what has occurred.
When you raise one finger (ides finger) to the questioning look from someone in a passing boat, you omit any specific information about what kind or how big that one was.
The occupant of the other boat, knowing that you are a great fisherman, will assume the best for you.
Just a borderline lie, really, hardly worth mentioning.
Lies about fish are by far the most common sort.
Adding a pound or two or a few inches to the fish is almost taken for granted, especially if the fish is already in filets and can no longer be measured accurately.
My fish is bigger than your fish is an important sort of claim, and if it must be bolstered with an incontestable fib, so be it.
As to why fishermen lie; that is a more difficult question. I have concluded, that at base, the cause is a form of envy.
The dictionary definition of envy doesn’t completely apply.
According to Webster, envy is, “resentful awareness of an advantage enjoyed by another, accompanied by a desire to possess the same advantage.
Fishermen are not generally resentful, but they most certainly desire to possess what the other fisherman has, even if he has lied about its magnitude.
Fisherman’s envy, then, is not the usual sort, and I would propose that it be given a slightly different sense.
I suppose we could just call it fisherman’s envy, but a psychological condition desires something more erudite using the Latin designation for fish we could call it piscatorial envy. Or if French might be preferred, it could be designated Poissonal envy.
Freud focused mostly on other human activities and did not comment on this specific sort of envy.
He did refer frequently to several related and similar sounding forms of the disorder.
I suspect that he knew about piscatorial envy and the web of small lies that it promotes, and I’m pretty sure he was not a fisherman.