I need to learn what?

If it's any consolation, the OED says of porgy that "Much vagueness appears to prevail in the use of the name." It then goes on to list a dozen or so different fishes sometimes called porgy.

I work on the assumption when reading that unless you really need to translate it into English, anything with a 鱼 or 草 radical will be some kind of fish or plant unknown to Western science and there's little point in looking it up.

Google and Wikipedia. Friends indeed.

http://en.wikipedia.org/wiki/Sparidae

http://www.fishbase.org/summary/speciessummary.php?id=445

Reminds me of trying to look up 趖 a few months ago. Try that one out and see if you get headaches. I saw it on a poster in a friend's Facebook picture as part of a phrase (閒趖晚日). Every definition I could find (only in Chinese) pretty much just quoted that passage, which turned out to be from a Five Dynasties-era poem by 歐陽炯 Ouyang Jiong. Other than that it's apparently used in Hokkien nowadays.

@roddy, good advice, along with 木 and 虫. In this case, however, it was in reference to those fish-shaped red-bean-paste-filled cakes one sees everywhere in Japan, and I just really wanted to know.

@OneEye, thanks! I gave up after that and didn't bother to check further. But I have heard of (and I think eaten) seabream, so now I think I have some vague idea of what they are.

In Japanese, those red-bean fish-shaped cakes are 鯛焼き, taiyaki, i.e. baked tai. I just think of the fish with their Japanese names (tai, toro, maguro, etc.). Don't really encounter the need to translate them - after all, restaurant reviewers often use the Japanese fish names too in English reviews.