hi, I think 漁民 and 漁夫 is very similar. even I can tall you that there is no difference. and yes, 漁民 and 漁夫 means who do it professionally. is a job, and also a kind identity. like 醫生 (docter)、老師 (teacher). and 捕魚者, actually. we seldom use this word.It is just the other way of saying a word for 漁民 and 漁夫. I can give you more explaination. 捕 is verb. is an action. means catch. 魚 is noun. means fish. 者 is noun. means the person who does the thing. Like the "er" in worker in English.

What do you call a person who fishes as a hobby every weekend then? 钓鱼爱好者，喜欢钓鱼的人。fish as a hobby 主要就是钓鱼吧。 他是个钓鱼爱好者，他是个喜欢钓鱼的人，他喜欢钓鱼，这三句话意思是一样的。 渔民、渔夫，靠捕鱼为生的人，也可以指职业。 “捕鱼者”就是“捕鱼的人”，渔民、渔夫和钓鱼爱好者（如果把鱼带回家的话）都可以称为“捕鱼者”，例如：在保护区内，警察抓到了几个非法捕鱼者。

We often use 渔民 to describe fishermen.捕鱼者 is to formal and it maybe long time ago when we used it.