Abstract
BackgroundIn this study, we report the first case of a male reef manta ray, Mobula alfredi, becoming sexually mature in captivity and present its reproductive characteristics.MethodsWe investigated changes in external morphology, behavior, and levels of steroid hormones in a male M. alfredi during its sexual maturation process.ResultsAt 2 years and 6 months of age, the male exceeded 300 cm in disc width. Then, at around 3 years of age, the male started to chase a female in the tank and exhibited androgen levels similar to that of another matured male, indicating that the study specimen had begun sexual maturation endocrinologically. Its first copulation event was observed at 5 years and 4 months and appeared behaviorally similar to field observations. Seven months after copulation, we performed a biopsy to collect its semen, including any motile sperm.ConclusionTaken together, these results indicate that the captive male M. alfredi individual shows signs of sexual maturation (size of disc width, testosterone levels, reproductive behavior) already with the age of 2.5 to 3 years. As a first copulation was observed with 5 years 4 months of age and the presence of sperm were confirmed at the age of 5 years 11 months of age, the studied animal reached its full sexual maturity at the latest at the age of around 5 years.
Highlights
In this study, we report the first case of a male reef manta ray, Mobula alfredi, becoming sexually mature in captivity and present its reproductive characteristics
Growth data of Disc width (DW) are shown in Fig. 1b: DW increased from the birth to 5 years and 6 months of age, after which it remained at ca. 345 cm until the end of the study
The testosterone level is already higher than in an immature animal, the animal did not show chasing or mating behavior at this time. These results suggest that age might be a more important factor than attaining sexual maturity size in M. alfredi
Summary
We report the first case of a male reef manta ray, Mobula alfredi, becoming sexually mature in captivity and present its reproductive characteristics. As fully-grown adults, they are among the largest ray species. Due to their tendency to aggregate predictably in relatively shallow waters around islands and along coastlines, they have become an attraction for recreational. The genus Manta was considered mono-specific, but was redescribed [3] in 2009 as comprising the reef manta ray, Manta alfredi (Krefft 1868) and the giant manta ray M. birostris (Walbaum 1792). In the present paper, the genus “Mobula” was adopted. Both species were listed as globally vulnerable on the IUCN Red List [5, 6]
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