The brain's pituitary is the undisputed champion of the endocrine system, credited with exerting more control over the growth of our body than any other structure. But a new contender has stepped into the ring—one that hits below the belt. Scientists have found for the first time that, at least in Mozambique tilapia (Oreochromis mossambicus), the gonads act as a "secondary pituitary," helping the fish reach their adult size. Without these sex organs—which produce sperm in males and eggs in females—the fish only grew to a fraction of their normal size, the team reports online this week in the Proceedings of the National Academy of Sciences. Transplanting gonads back into the tilapia—even into nonsense locations such as the fish's back—allowed the animals to grow again. The findings may apply to all vertebrates, including humans, the team reports. They could also be a boon to fisheries, which struggle to keep fish from breeding before they have reached the size at which they can be killed for food.
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