After about a year they've reached "adult size" Females are breedable at 50 or 55 grams and it's best to wait until they've reached that 1 year old mark. Leo's will continue to grow a little bit and put on weight after that point though.
The Tremper giant strain can reach weighs of over 100 grams.
However, I have an adult pair of leo's which are 74 grams at this time and they are not related to the tremper giants.
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