In some darts the males start calling months before they're mature (practising so they have it right when the time comes?
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I had powder blues and azureus males calling by 8 months, but no way were they sexually mature at that age.
Some people do manage to get their male darts to mature by one year, usually it's the result of power feeding (not really a good idea). Like Double J, I've heard they mature around 18 months.