Fish seem to be a very important component of the most healthful human diets, AFAIK, likely/mostly grounded in various aspects of evolution - some more on the side of actual 'selection pressure', some more on the side of chance and 'doesn't break things in a way that really matters' (i.e., successful enough reproduction / survival until ages required for reproduction).

That said, and in light of the comment from https://news.ycombinator.com/user?id=AlecSchueler, in particular - many of the most essential nutrients / 'micronutrients' that are obtained from eating fish are actually not made by fish themselves. Rather, fish 'concentrate' these substances as they go about their own business of survival. For example, vitamin D3, DHA, EPA, etc. Consequently, there are much more readily available 'vegan' sources of these substances, derived directly from the fundamental source(s) - microalgae and the like.

FYI (to all).

Overfishing IS a serious problem. Our activities, in general, are at a scale, and grounded in processes, these days, that produce significant impacts on the environment. Frankly, in the 'great scheme' of things, it doesn't matter a whit. Humans, and even this planet, are not even a droplet in the ocean of the universe, as far as we / I can even get any sort of a solid handle on that concept, now. But, that doesn't absolve us of any responsibility for trying not to absolutely annihilate OUR home.

It's disgusting to be GIVEN so much (none of us had much hand in almost anything that exists now, even what we've 'built' - we can't create atoms, we don't choose when, where, or to whom we are born, many of the opportunities we are afforded in a 'given life', etc.), and treat it as casually as so many do - to be so entitled as many seem to be.

But then, the universe (/ God / gods / whatever concept you prefer) will always have the final say. It'd just be nice to not F things up for everyone else, IMO.

EDIT: I hope the latter bits, above, don't come off as too moralizing - not my intention ... it's difficult to avoid some frustration with some of what the news inundates us with every day, I find.

More importantly - vitamin D3 is also readily produced in our own bodies with enough of the right kind of sunlight (dependent also on skin tone, age, kidney & liver function [etc.], and, ultimately, 'height of the sun in the sky' - i.e., enough ~290-300nm UV rays penetrating the atmosphere at the angle of inclination / solar zenith angle / whichever concept/quantification you prefer). And, this is actually not much at all. While skin cancer is, itself, a risk - this should, of course, be weighed against the importance of vitamin D3 itself. This comment is already REALLY long, but basically, for latitudes close enough to the 'Tropics', typically only 10 - 20 minutes of sun around noon in summer would be necessary. Winter is trickier. Here are a few links that may be useful for more info (in general, Pubmed - searching for review articles, etc. - is usually a good place to start, IMO - depending on how comfortable you are with reading these types of articles, otherwise, backtracing to those that cite them, especially, the efforts at more 'popular press' descriptions of research now produced by journals like Science etc.):

https://pubmed.ncbi.nlm.nih.gov/32918212/

https://pubmed.ncbi.nlm.nih.gov/28516265/

https://academic.oup.com/ajcn/article/110/1/150/5487983

... The 'Linus Pauling Institute' also seems to have, in my past experience, quite good information on 'micronutrients', in particular (with good citations, etc.), for all of Pauling's actual more tenuous beliefs (himself, in later life) about vitamin C:

https://lpi.oregonstate.edu/mic/vitamins/vitamin-D