Tilapia have a period of accelerated growth that begins at hatching and lasts for roughly 240 days, or 34 weeks. After this period, the growth rate flattens out for the remainder of the tilapia’s life, eventually gaining only a few ounces per year. This is important to the tilapia farmer because during this period, the feed to growth ratio is optimal. In other words, during the first 240 days, a pound of food yields a pound of fish. After this period, the farmer will rapidly get less weight gain for every pound of feed given. To answer your question with a number, it takes 240 days, or 34 weeks for food grade tilapia to reach a 16 to 20 ounce harvest size. Food grade tilapia are simply those tilapia that exhibit the fastest rates of growth.
It’s important to remember that a big chunk of that 240 days is spent in the hatchery, not in the grow-out. Hatcheries like Lakeway Tilapia offer commercial farmers services such as holding fingerlings until they are 30 grams each. By doing this, the amount of time that the tilapia farmer has until harvest is reduced to less than six months, or two harvests per year from the same pond.