Yes, there is a difference:
if you can count it - one fish - "рыба", from two to four - "рыбы", five and more - "рыб". For example -fifteen fish - "пятнадцать рыб", give me three fish - дай мне три рыбы.
If a lot of fish, you may say - много рыбы (a lot of fish). If you want to say "many fish" (many types of fish) - много рыб.
But if you can't count the fish (or you don't want to count) - correctly to use in the singular. For example: Рыбаки пошли ловить рыбу сетями - the fishermen went to net fish.
So "The fish are on the table" would be the same as one fish - "Рыба на столе". Next time press report -> my answer should be accepted.
Ы is a specific Russian vowel. You can look it up on https://forvo.com/search/%D1%80%D1%8B%D0%B1%D0%B0/ to listen to pronunciations