Except that is not really true:
One commonly cited reason is that of health, based on findings that red meat is detrimental to health in many cases due to non-lean red meats containing high amounts of saturated fats, choline and carnitine. Eating certain kinds of fish raises HDL levels, and some fish are a convenient source of omega-3 fatty acids, and have numerous health benefits in one food variety. A 1999 meta-analysis of five studies comparing vegetarian and non-vegetarian mortality rates in Western countries found that in comparison with regular meat-eaters, mortality from ischemic heart disease was 34% lower in pescetarians, 34% lower in ovo-lacto vegetarians, 26% lower in vegans and 20% lower in occasional meat-eaters.
Source:
https://en.wikipedia.org/wiki/Pescetarianism