I don't think I fully understand your question, but I'll explain some things regarding collective nouns: What you're describing Is a actually called "اسم الجنس الجمعى" (Collective Generic Noun), not "اسم الجمع" (Collective Noun), so, what's the difference ? A collective noun is a word that describes a plural that doesn't have a singular variation, for example, the word "نساء" means "women", you can't get a singular variation from this word, for a singular woman we use the word "امرأة" which is a completely different word, so the word "نساء" actually have no singular, same with "إبل" "camels", again, no singular form, a singular camel is "جمل". The Collective Generic Noun (CGN) is a word that describes a plural, which gets its singular variation by adding the letter "ة" at the end of it, like the examples you gave "تين - تينة" "سمك-سمكة" and so on. So now, what's the difference between a CGN and a normal plural ? Generic nouns don't describe multiple objects, they describe the "kind" of object, for example: سمكة - singular - a fish سمكات \ أسماك - plural - fishes (multiple) سمك - CGN - fish (in general) So the CGN is used when you mean the kind of thing, "I like fish أحب السمك" , but the normal plural is used when you mean a certain number or amount of the thing "I ate 4 fishes أكلت 4 سمكات", you can't describe a CGN with a numerical value ( unless you use a preposition like : I ate 4 OF the fish أكلت 4 من السمك ) . So, to recap with another example: "ورق" (CGN) means paper (in general), if I say "ورقات or أوراق" (normal plural) I mean (sheets of paper), the singular is: (CGN+ ة ) = ورقة (a sheet of paper). And finally, another difference between the two is that: All (non-human) plurals take singular feminine pronouns (ex:هذه سمكات) All CGNs take singular masculine pronouns (ex:هذا سمك) I hope I cleared up some of the confusion (or maybe I added even more ?), if you have a specific question about kinds of plural for example please post them in a separate question.

So to my understanding, collective nouns are of two patterns. Number 1) in languages there are words which are singular in form but denote a set of things. For example in English you have the words of classes e.g. class, herd, team, group, family, audience all which are considered collective nouns because they are composit beings in each they share the same identical units. As far as I know, this applies to Arabic but the usage in Arabic differs from in English in that we use certain forms of plurals with units and plural forms in English on the other they are unchanged but in Arabic they "can" change like مجموع السمك e.g a group of fish used with سمك and not with سمكة. However in AR. there are also those types of collective nouns which are unchanged and show homophony with their singular forms.TWe need to look them up to learn each separately. غَنَم: (اسم (singular same with collective ) الجمع : أَغنام ، و غُنُوم (plural) الغَنَمُ : القطيعُ من المَعْز والضأْن، ،مفرد شاة (collective same with the singular)، (the lamb is a flock of goats etc.) therefore قطيع من الغنم. Another one is a herd horses رعيل من خيل خَيل: (اسم) (singular same with collective) الجمع : أخيال ، و خُيُول الخَيْلُ : الكِبْر والعُجْبُ بالنفس (collective same with singular) الخَيْلُ :جماعة الأفراس (لا واحد له من لفظه) Where in both examples the words here that appear as غنمة and خلية are not attested as singular though they are same in form with singulars. Number 2 since the ة ending makes some words uncollective or their reduction making them collective, it remarkably equates to the sense of a count def. in English noun denoting a class of things. The cheetah is the fastest animal, the fish is the most interesting animal or the apple is the tastiest. All that what signifis here is a set of things from the same members hence سمك not سمكة the fish (class of animals) or تفاح and not تفاحة the apple (class of fruits). I hope that helps.

Unfortunately it has no rule at all 'cause أسماك also means Fishes I'll explain..... Food means "طعام" and it's plural (foods) is called "أطعمة" this is called "جمع تكسير" there are 3 types of collective nouns: 1:جمع مذكر سالم That ends with ون or ين 2:جمع مؤنث سالم This one is much easier as it ends with ات 3:جمع تكسير May God be with you By practicing you'll know them all, even you'll make rules yourself The older you get the more you understand. You must give it time, believe me this can't be done in a day and night P.S. Ask your teacher to clarify, I'm pretty sure you'll understand better by hearing

Don't bother yourself, Just focus on grammar. Good luck :D