they take about a year those are left from last year i picked them up from the bottom of the canals here where i live every winter when they drain the canals so each barrel has the bottom full of clams along with the pond u see there with the shrimp and self cloning crays they range in size from 1/4 to those that u see 4inches but the small one i leave in the barrels and like i said about a year later they grew to there max size but not the giant clams thy take a bit longer but they breed in there also i fined there babies in the filters all the time about 1/8inch in size