" سمك " it's more than 2 fishes " سمكة " one fish " سمكاً " it's more than 2 fishes , it's the same as " سمك " but it's all about the grammar and it depends on the sentence for Example " أكلت سمكاً " here " سمكاً " is the object , so you added " اً " to it but in this "هناك سمك في البحر " you didn't add " اً " because " سمك " is the subject but it needs more and more study , because Arabic grammar is a little hard Good luck ^^

سمكة means fish for singular nouns in arabic if the noun is female we add (Haa ) and you pronounce it as Samakaah سمك for plural noun and this kind of nouns called in Arabic "Gam taksiir" to make it easier i'll give you an example; "Student-طالب " when you make it plural in Arabic you find 2 types for females we say "طالبات" and Gam Taksir"طلاب" Which includes the females and the males . ( So when you find a singular feminine noun and want to make it plural you do the Gaam Taksir way or you add (ات-) to the word . About the last part, it's not so different than Gaam Taksir all you do you add "اً" to the plural word in Gaam taksiir to make it fit the pronunciation . Hope This helps, Good luck

سمك means more than 2 fishes سمكة means 1 fish سمكا means more than 2 fishes سمكة means 1 fish Actually your 2nd question is tricky, you don't have to understand how, just be aware of it 'cause It's too difficult to explain by typing, you need to hear and write down what you concluded