Trimma caudomaculatum, the blotch-tailed pygmygoby , is a species of goby from the Western Pacific. Like other members of the genus, they are usually found in large schools in the sloping or vertical drop-offs at coral reef edges. Similar to other species of Trimma this species consists of multiple cases of bidirectional sex change, meaning that if a group is lacking in a specific sex a partial amount of the group can change their undeveloped gonad structure of the opposite sex in order to accommodate. This sex change is made possible due to the females having a developed set of ovaries with female hormones that are developed, and a set of testis and male hormones that are underdeveloped; The males follow a similar set up in vice versa, so their testis and male hormones are developed, while the ovaries and female hormones are underdeveloped.

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