Sexual dimorphism

Adult Radiated Tortoises usually show a distinct sexual dimorphism. In captivity, sexual maturity usually sets in earlier than in the wild due to consistent, good conditions. Females become sexually mature at 15 years of age, a body size of at least 24-26 cm and a weight of at least 5 kg. Males do not mature until 20 years of age, a body size of 30 cm or more, and a weight of over 8 kg. Males seem to reach sexual maturity much later than females. Presumably, they cannot successfully reproduce until they reach a certain size and have gained experience. Females do not cycle under unfavorable conditions, e.g., absence of seasons, or lack of light. Hormonal release and reabsorption of egg follicles in the body of female ray turtles is possible.

  • Adult males have a concave plastron, a long, sickle-shaped tail, bulging, squat anal shields with a wide angle, and sometimes slightly more pronounced gular shields. Adult males are proportionally larger and heavier than females.

  • Adult females have a rather flat plastron, a short spindle-shaped tail, flat anal shields with a rather acute angle, and a less pronounced gular shield compared to the male. Heads of females are sometimes slightly narrower and proportionally females are smaller and lighter than males.

Sex determination

For many turtle keepers it is important to have an overview of the sex distribution in the population when assembling a breeding group. Since a clear expression of the sexual characteristics in Astrochelys radiata starts only late with sexual maturity, in captivity about 15 years, a sex determination of juvenile specimens on the basis of external characteristics is often very difficult and needs some experience and expertise to be able to make a reasonably safe prognosis about the sex. There are also specimens that show contradictory external sex characteristics. For example, there are females that have a concave plastron and males that have narrow anal shield angles and small tails.

Sometimes young females show clear beginnings of anal bulges around the cloaca early on. This sac-like and extremely stretchable tissue is more pronounced in females than in males. It probably serves to squeeze large eggs out of the cloaca more easily and without injury. Juvenile males can sometimes be stimulated to eject the penis from the cloaca by gently showering warm water over it. The tip of the penis is also sometimes briefly visible during relaxed bathing in warm water or urination. A bulged and erect penis of an adult male may be 2/3 of the total carapace length.

With young animals from a body weight of 300 gr, it is possible to determine the sex with the help of an endoscopic examination. The tortoise is anesthetized and an endoscope is inserted into the abdominal cavity through a small incision in the fold of the knee. The surgeon then carefully searches the abdominal cavity for testes or ovaries using the endoscopic camera and a monitor. Although the risk for this procedure is considered low, endoscopic examinations should only be performed by experienced professionals. Follow-up care consists of monitoring the animals in the following days and checking the endoscopy wound in the fold of the knee. In order to check the sex distribution in different brood schemes, we selectively use the possibilities of endoscopic early sex detection in selected young animals in our breeding station.

It is estimated that 2/3 of all captive Radiated Tortoises are males. Due to too low breeding tempeartures, however, males continue to be born more often. Females appear to be more sensitive and susceptible to stress in husbandry and care than males due to hormonal processes. Probably the mortality of females is also much higher than in males due to deficiency symptoms and husbandry errors.

FAQ on the topic of gender

FAQ "...May I send you a picture for sexing our Radiated Tortoise?".2022-04-12T12:24:07+02:00

Yes, you are welcome to send pictures of your Radiated Tortoise for sex determination. From experience we can usually make a relatively safe statements about the sex of larger animals. With small animals, however, a sex determination from the picture is a challenge even for us and usually not possible. Often only a tendency can be made out. In order to be able to determine the sex as precisely as possible, a good image quality with an optimal shooting angle is a prerequisite. Also crucial is the degree of relaxation of the intimate area of the pictured tortoise. For sex determination we need a clear image of the anal region and a view of the plastron. Especially the tail with the cloacal opening, relaxed and not attached to the body, should be clearly visible.

Please note that a sex determination from a picture always allows for misinterpretations and therefore we can not make any binding porognoses about the sex. If interested in a non-binding assessment, send the image material by e-mail to We will get back to you within a reasonable period of time.

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