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Its really a jugment call the longer you have fish in a tank, or choose to breed fish the more knowledge you will aquire in being able to determine to some degree how old a fish, or school of fish might be,if a fish looks old it probaly is, length and width will get you somewhat close combined with a good close once over visual. If you have any fish books you can find what type of fish you have in the book and the book will tell you every thing you need to know how long the fish will get when it gets to a mature age. Some fish live a long time.

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19y ago

What else can I help you with?