"Fishes" can sometimes be used for the plural of "fish".
No, that's not how "gli" is used.
This link should help explain when to use what article. Bear in mind, though, that the rules for
gli are similar to the rules for the English "a/an" -- it's the very next word that matters. So while it would be "l'ape" and "gli aerei", it would be "la mia ape" and "i miei aerei".
In linguistics, holding a sound for extra time is called "gemination" (or in the case of stop consonants that can't actually be continued like that, "delayed release"). It's not actually being pronounced twice.
If anyone is interested, I can explain why Italian has geminate consonants. :)
I would love to read your explanation. Italian will be my third latin language, but the first one to have gemination. And as another person already noted, in English we are taught that doubling consonants is only a spelling issue. (At least that is what I was taught as a child 5 years ago in California).
In English, writing double letters usually indicates a difference in the pronunciation of the previous vowel. Later vs latter. Biter vs bitter.
Syllables can have an onset, a nucleus, and/or a coda. For example, the syllable "can" has all three, the syllable "ma" has just an onset and a nucleus, and the syllable "if" has just a nucleus and a coda. Some syllables have consonant clusters, which give them extra weight: "its" for example has a nucleus and a complex coda. (As a side note, the nucleus does not have to be a vowel. It just has to be the sonorant peak of the syllable. But that's beyond the scope of this discussion.)
To see where Italian gemination comes from, we need to look at how Latin evolved into Italian. But since this is not a dissertation, we'll just look at one illustrative example.
The Latin word for "eight" is "octo". It's where we get our prefix from: octopus, octagon, etc. The Italian word for "eight" is "otto".
As Italian grew out of Latin, the phonotactics became such that certain consonant clusters stopped being clusters. When one sound changes to become like another sound, that's called assimilation.
But the phonotactics wanted the syllables to keep the same moraic weight. And this is why we say that assimilation happened and not outright dropping. And that is the quick and simple explanation of gemination in Italian.
(il) gatto is a mas. noun. it covers all male cats and all cats of unknown sex. (la) gatta is a feminization when you know the cat is female. le gatte is a feminization for a group of cats known to ALL be female. i gatti is for a group of cats of unknown sex or a group with a ANY male.
This should explain the definite articles in Italian:
Nouns are always their own gender, regardless of anything else. It's the articles and other adjectives that describe it that must modify to agree.
La donna (feminine, singular) ha i gatti (masculine, plural).
Gli uomini (masculine, plural) hanno la gatta (feminine, singular).
Don't think of it as man vs woman. The labels are "masculine" and "feminine". And 99.99% of the time, grammatical gender has absolutely nothing to do with biological sex. It's why linguists prefer to call them noun classes. Some languages have systems where the labels are not "masculine/feminine" at all.
Italian is fairly regular when it comes to how word forms reflect noun class. With very few exceptions, if a noun ends in:
-o then it's singular masculine
-i then it's plural masculine
-a then it's singular feminine
-e then it's plural feminine
The rules for what definite article to use are regular, although slightly complicated. This link should explain it: http://www.oneworlditaliano.com/english/italian-grammar/italian-definite-articles.htm
I'm guessing that you're asking about grammatical gender? "This" is pretty vague.
Only common farm animals and pets get individual masculine-feminine distinction. All other animals have one grammatical gender for the species, regardless of the biological sex of the individual.