The fish you have purchased is a White sturgeon, reaching weights of over 1000lbs in the wild. these fish must also be fed nearly constantly (i feed mine 7 times a day) with a nutritious food such as a mysis and blackworm mix.
also, if you have not already, disconnect your heater as these fish can tolerate warmer water but should be kept at as cool as you can get it. these fish make himantura pups and african arowanas look easy as far as fragility and food consumption (respectively of course).
i wish you luck with this potentially huge monster. you are going to need it. very few of these fish survive past the 3 week mark in the average aquarists tank.