It's not a simple yes or no answer. Many fish species exhibit complex reproductive strategies, meaning that their sex at birth isn't always a fixed characteristic.
The Variety of Sex Determination in Fish
Some fish species are born exclusively male or female, like many commonly kept aquarium species. However, a significant number of fish species are hermaphrodites, meaning they possess both male and female reproductive organs. There are two main types:
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Protogynous hermaphrodites: These fish are born female and can later change to male. Examples include the Indo-Pacific cleaner wrasse (as mentioned in the Berkeley Evolution website), and clownfish, which are all born male but can transition to female, as detailed in the Reddit post. The BBC Earth article further exemplifies this with the kobudai. This process is described by the phrase "female first" in the provided texts.
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Protandrous hermaphrodites: These fish are born male and can later transition to female. Snook, for example, are protandrous, with most males changing sex by age seven, as noted by the Florida Oceanographic Society.
Other fish species have a more straightforward gender determination, meaning they are born and remain a single sex throughout their lives. However, even within these species, environmental factors might influence sex ratios. One example of this complexity is provided by UF/IFAS One Health.
The statement from the reference about protogynous fish, "some fish will start out lives as male, some will switch from female to male at some point, and some will remain as females for the full duration of their lives", perfectly captures this diversity. It highlights that even within one type of hermaphrodite, individual variation exists.
Finally, it's crucial to remember that many times, observed sex changes are misidentifications of sex, as mentioned in a post from the Cichlid Forum. Accurate sex identification in fish can be challenging.
