Endocrine responses of Tilapia (Oreochromis mossambicus) females to male pheromone(s)

Rato, Ana

http://hdl.handle.net/10400.1/3602

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Authors

Rato, Ana

Advisor(s)

Canario, Adelino V. M.

Hubbard, Peter

Abstract(s)

Several lines of evidence suggest that male Mozambique tilapia (Oreochromis mossambicus) release a reproductive pheromone via their urine. A recently identified steroid glucuronide, present in male urine, is probably one of the active components that increase levels of a steroid hormone responsible for oocyte maturation, 17,20β-P, in females. The aims of this study were to identify which fraction(s) of male urine is responsible for this increase and whether the steroid glucuronide is sufficient, on its own, to cause a similar increase in 17,20β-P metabolism. Pooled male urine was passed through C18 extraction cartridges, thus obtaining the filtrate (aqueous/polar) and eluate (hydrophobic/non-polar) fractions. Females were exposed to urine, its respective fractions, and the steroid glucuronide (and in combination with each-other). One hour after exposure, water samples were collected and steroids extracted. The same experiment was conducted in males, using a urine pool from dominant males. Steroid levels (17,20β-P, cortisol, 11-ketotestosterone, and testosterone) were measured by radioimmunoassay. Exposure to male urine, its eluate, and the steroid glucuronide (and combinations containing the eluate or steroid) evoked a dramatic increase in release rates of 17,20β-P by females. The filtrate alone had no such effect. In males, release rates of 11-ketotestosterone, but not testosterone, increased after exposure to male urine. These results suggest that the pheromonal activity of the urine is contained wholly in the C18 eluate. Furthermore, the steroid glucuronide (originally isolated from the urine eluate) is sufficient, on its own, to cause an increase in levels of 17,20β-P metabolism. Thus, the steroid glucuronide is responsible for the pheromonal activity of male urine, at least in this endocrine effect in females. The endocrine response of males to this urinary pheromone requires further investigation.