Nearly 300 tilapia are growing in rooftop tanks at a Brooklyn business that hopes to someday sell the fish to retailers.

VertiCulture Farms has been operating since 2012, but has been at the old Pfizer building at 630 Flushing Ave. for about a year.

The company recently began fish farming and hopes to be the largest commercial indoor aquaponics farm in the city. The founders say they are practicing a form of sustainable farming in which the fish help fertilize herbs, such as basil and mint, that they also grow.

The fish that are currently growing will take at least five months before they are considered big enough to be sold to retailers.

The fish farmers picked tilapia because the species is resilient. They say they are open to trying others.

VertiCulture says it may seek out new locations as it grows.