For example for 本名 it gives me ほんみょう as the pronunciation but also ほんめい。
Another example: for 魚 there is さかな but also うお given as pronunciations.
Well I guess the first pronunciation is the most commonly used but what’s the deal with the other ones? Are there like different dialects? Are there interchangable and you can use the pronunciation you “feel/like” more?
When would I for example say 海にたくさん魚（うお）がいます。instead of 海にたくさん魚（さかな）がいます。
4 comments
Unless it says “slang” or “archaic” or some other hint next to it, in my experience you kinda have to google when this happens for instance, your example of 本名
https://japanese.stackexchange.com/questions/21504/%E5%AE%9F%E5%90%8D-vs-%E6%9C%AC%E5%90%8D-connotation
Ok so this is yet another EDICT based dictionary, which is to say it doesn’t know. The vast majority of apps and websites aimed at learners use EDICT which is unfortunate as while it is very comphrensive, it is not laid out in a way designed for beginners.
Compare the entry in the Japanese-English dictionary on goo on the other hand:
https://dictionary.goo.ne.jp/word/en/%E9%AD%9A/#je-5141
For 本名 one way would be to see if it comes up in your IME but again, goo dictionaries either simply redirect ほんめい to ほんみょう or simply leave it out as an option entirely.
As for 本名, I’ve never seen or heard of that as ほんめい.
When I hear the sound ほんめい, my mind reminds me of Kanji 本命(ほんめい).
本命 can be used in a few ways but I mainly use it as the meaning of this :
俗に、その人にとっての第1候補。最も望んでいる対象。「本命の大学に合格する」「 本命チョコ vs 義理チョコ」
In common parlance, the first choice for the person. The most desired object. “Getting into the university of one’s first choice” , “Honmei choko/chocolate to give to someone one really likes vs. Giri-choko/chocolate to give to company or male friends regardless of love.”
As for 魚, when you want to say just fish, it’s always さかな.
うお is used in like 魚座(うおざ) as the meaning of Pisces as in 12 sign, 魚市場(うおいちば) as fish markets, 魚河岸(うおがし) and stuff.
When it comes to kanji compounds, 魚 tend to be read as うお.
However I think 魚屋さん is さかなやさん lol
Sometimes two different words can be written with the same kanji. If it helps, maybe imagine how “lead” and “lead” are two unrelated words with different pronunciations that happen to look exactly the same. Unlike this, though, at least in Japanese they’re usually related to each other. Sometimes there’s older or alternate/archaic pronunciations. Apparently 本名 can also be read ほんめい according to my dictionary, but I’ve never heard it before. うお is actually the original word for fish, but was mostly replaced by さかな, which actually comes from 酒菜 (ie a snack to accompany drinks). But うお is still part of certain phrases or names of certain fish like the flying fish. 飛び魚 (tobiuo).