Andre Seale (Department of Human Nutrition, Food and Animal Sciences) and collaborators have published two new studies on aquacultured tilapia, a common and adaptable farmed fish in the Islands.
In “Sex, Salinity and Sampling Period Dependent Patterns of Growth Hormone mRNA Expression in Mozambique Tilapia,” published in Aquaculture, the authors point out that one reason tilapia are the second-most aquacultured finfish group in the world is their tolerance to a wide range of environmental conditions, as well as their sexually dimorphic nature, where males grow larger than females.
But what makes them grow? As in other vertebrates, growth in tilapia is regulated by the growth hormone/insulin-like growth factor (GH/IGF) system. Moreover, environmental salinity has been shown to directly modulate growth in tilapia. Less is known, however, about how salinity may modulate sexually dimorphicgrowth specifically.
Studying the Mozambique tilapia, Oreochromis mossambicus, the authors compared the expression of pituitary growth hormone of male and female adults reared in fresh water, seawater, and a tidal regime characterized by dynamically changing salinities between fresh and salt water every six hours, over a 24-hour period.
They found significant effects in terms of sex, salinity regime, and whether fish were sampled during daylight or dark. These results provide insight on the sex-specific modulation of growth hormone expression by environmental factors in Mozambique tilapia.
Andre’s other paper, “Early-Life Exposure to 17β-Estradiol and 4-Nonylphenol Impacts the Growth Hormone/Insulin-Like Growth-Factor System and Estrogen Receptors in Mozambique Tilapia, Oreochromis mossambicus,” was published in Aquatic Toxicology, a leading peer-reviewed journal.
It’s widely recognized that endocrine-disrupting chemicals (EDCs) released into the environment through anthropogenic activities can negatively affect aquatic organisms. These have short-term impacts on physiological and behavioral processes – and sustained or delayed long-term effects on development. Many studies have characterized the effects of EDCs on temperate fishes, but less is known about their effects on the growth and reproductive physiology of tropical species.
To determine the long-term effects of early-life exposure to common estrogenic chemicals, the authors exposed Mozambique tilapia yolk-sac fry to two EDCs and looked at the expression of genes involved in growth and reproduction in adults. They concluded that tilapia exposed to these two estrogenic chemicals at this early stage of development exhibit subsequent changes in the endocrine systems that control growth and reproduction during later life stages.