Following observations of my own fish seemingly changing from a female appearance to a male appearance, I have done some brief web searches. Searching for "tetra sex change" - even without mentioning the exact species in the search - has brought up a number of anecdotal accounts of black phantoms (Hyphessobrycon megalopterus)changing from female to male appearance and vice versa.
As far as I am aware, there are no definitive studies showing any characins to be capable of changing gender. However, that doesn't mean it doesn't happen.
There are alternatives - the anecdotal accounts (including my own) only observe the secondary sexual characteristics of the fish, i.e. colouring of fins and the shape of the dorsal fin. So there are several possibilities:
1. The fish do actually change sex
2. The fish do not change sex, but are capable of displaying colouration of either sex under conditions and circumstances unknown.
3. The identification of females as red finned and males as black finned is simply wrong and there is no particular sexual dimorphism, instead the dimorphism is based on other factors (for example, dominance in the heirarchy etc.)
Although point 3 seems rather unlikely, this sort of mistake has happened before, even in mammalian biology (such as the male and female coati being identified as two seperate species).
Without slicing my fish open to observe their reproductive organs, which I am reluctant to do for obvious reasons, even if it's for the advancement of science, it is not possible for me to verify or disprove point 1. Personally I believe point 2 to be the most likely. More data is needed, ideally from people who have kept this species for longer than I have, and in a setting where they are able to definitively identify every fish in the shoal (with only a small number of fish this is easy, but if you have a shoal of 20 it would be nigh on impossible).
As far as I am aware, there are no definitive studies showing any characins to be capable of changing gender. However, that doesn't mean it doesn't happen.
There are alternatives - the anecdotal accounts (including my own) only observe the secondary sexual characteristics of the fish, i.e. colouring of fins and the shape of the dorsal fin. So there are several possibilities:
1. The fish do actually change sex
2. The fish do not change sex, but are capable of displaying colouration of either sex under conditions and circumstances unknown.
3. The identification of females as red finned and males as black finned is simply wrong and there is no particular sexual dimorphism, instead the dimorphism is based on other factors (for example, dominance in the heirarchy etc.)
Although point 3 seems rather unlikely, this sort of mistake has happened before, even in mammalian biology (such as the male and female coati being identified as two seperate species).
Without slicing my fish open to observe their reproductive organs, which I am reluctant to do for obvious reasons, even if it's for the advancement of science, it is not possible for me to verify or disprove point 1. Personally I believe point 2 to be the most likely. More data is needed, ideally from people who have kept this species for longer than I have, and in a setting where they are able to definitively identify every fish in the shoal (with only a small number of fish this is easy, but if you have a shoal of 20 it would be nigh on impossible).
