Even at this young stage, you'll see a large discrepancy in the size of the fry. The largest tend to be male and they also tend to become the alphas - those who are more aggressive or assertive when feeding and when mating. The smallest tend to be females, who will not get nearly as large as their male siblings.
Each batch by these parents tend to be half black marble and half white marble. They will go to the pet shop for sale when they are between 8-10 weeks old. At that time, they are completely weaned off brine shrimp and are eating fish flakes, and their bodies are around the size of a quarter. Anything smaller than a quarter-sized body often results in high fatalities, as each move to new water stresses the youngest fry.