ho - This information is usually found on food packaging, and can also be obtained from vendors at pet stores or from veterinarians. You can also google this information.

red8 - If you put in a little more effort and went a little further than this forum, you would have been able to google for a long time and find all the information you need. There are many useful articles on your request, for example, https://pawfectpawprint.com/how-long-can-betta-fish-go-without-food/ . Check it, I think this is what you are looking for.