In some Mediterranean fish, sex is not settled at birth. The gilthead sea bream begins its reproductive life as a male, while the dusky grouper starts out as a female. How does that work?
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The gilthead sea bream matures first as a male, then becomes a female from its second year of reproduction. This change happens only once rather than repeating from year to year, and it has been documented through genomic and genetic studies.
The dusky grouper follows the opposite path. All individuals begin their adult life as females, and some of them become males as they grow, generally at around 80 to 90 cm in total length. The age at which this happens varies between studies, from 7 to 17 years according to one review.
Researchers have also noted that intensive fishing seems to shorten the age and size at which the change occurs, though this remains a debated possibility. This endangered fish shows how fragile these life cycles can be.
