Ultrasonographic imaging of the reproductive organs of the female bottlenose dolphin, Tursiops truncatus aduncas

Routine ultrasonographic examination of the reproductive tract was performed for periods of up to 10 years in ten female bottlenose dolphins (Tursiops truncatus aduncas) in Hong Kong. The ovaries could be reliably and repeatedly identified, lying close to the body surface, in the angle formed by the rectus abdominus and hypaxialis lumborum muscles, and were most easily located by scanning in the transverse plane from the proximal end of the genital slit towards the head. The ovaries are ovoid, with a relatively hypoechoic cortex around a central echogenic mesovarium. The echogenicity of the ovarian parenchyma appeared to increase with increasing age. This may be the result of age-related changes, such as increased fat deposition or fibrosis, or of ovarian 'scars' from multiple ovulations. Small antral follicles, developing follicles and corpora lutea can be identified within the ovarian cortex. Owing to its shape and lack of a definitive border, plus the close relationship to the intestines, the contents of which may obstruct the ultrasound beam, the non-pregnant uterus was not so easily visualized. The endometrium was poorly differentiated and difficult to see. To date, examination of the uterus using ultrasonography has provided little information about endometrial changes during the ovarian cycle in this group of dolphins. Real-time diagnostic ultrasonography provides a means to image the morphology of the reproductive organs in live female dolphins directly and provides a valuable means of assessing reproductive events in this species.

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