Size matters in commercial fish production. Species such as tilapia are known to exhibit sexual dimorphism, or sex-specific differences in body size, with males outgrowing females. As can be expected, tilapia producers have long employed a variety of approaches to favor all-male production.
But what are the mechanisms controlling such sex-specific growth disparities? Recent work in the Laboratory of Fish Endocrinology and Environmental Physiology, part of the Dept. of Human Nutrition, Food, and Animal Sciences, may shed some light.
The investigators began by measuring several genes involved in the hormonal control of growth and reproduction in fish. They employed an experimental model that allows for observing the whole-body effects of growth hormone, a major driver of growth, and luteinizing hormone, which is key for the development of gonads.
By combining the injection of these two hormones, the investigators successfully restored the gonads to normal size after they had been experimentally regressed. The investigators also discovered that growth hormone, its receptor and insulin-like growth factors, which form a major part of the GH/IGF system, are differentially regulated between sexes – and this is consistent with the differences in growth rate between sexes in the tilapia species.
“We found that the expression of growth hormone receptor and IGF was more sensitive to growth hormone in muscle and liver of male tilapia,” says Andre. “In females, the combined actions of growth hormone and luteinizing hormone appeared to be key for ovarian development. Together, these findings provide insight into the hormonal basis of sexually dimorphic growth in fishes.”
Read more of Andre’s study, “Sex-specific responses to growth hormone and luteinizing hormone in a model teleost, the Mozambique tilapia,” in the latest General and Comparative Endocrinology.
Photo: Male tilapia on left and females on right of the same age.