# Protogynous hermaphroditism in Cardinal tertas (also other Tetras?).



## Nick_593 (15 Mar 2013)

Hello everyone,

Just made some observations with the fish I have in my tank. I have 8 Cardinal tetras in my tank, and there is always just one that is much larger than the others. A few weeks ago the largest one died, and within 4 to 8 days, one of the others grew to be much bigger than the rest, very rapidly(!). Then, just one remains far larger than the rest of the Cardinals. I have seen this happen a few times over the years, and this idea popped into my head looking at my tank today.

Protogynous hermaphroditism is an alternative mating strategy which allows individuals to pass on their genes more efficiency, when there is high competition to breed between males. So in fish, it is sometimes best to start off as female (pass on genes if you cant compete with the bigger males), then change to a male when you have a better chance to compete (by becoming male you pass on even more genes than females if your able to become the biggest male in the pecking order). So in the Cardinal tetra, I am wondering if the second most dominant individual in a harem changes sex from female, to male, to basically become 'top of the pecking order', as in nature males pass on more genes than females in many cases. This is process quite common in marine fish, and some freshwater. But wondering if this applies to any tetras.

I'm wondering if anyone has noticed similar observations to me with their tetras (i.e. has anyone noticed that one of their tetras is much larger than the others in the tank- a stack contrast?)? I'd say this applies to 10 or less fish (or thereabouts!), as I don't know how big a harem would be with these fish.

Would be interesting to know other peoples observations with their tetras?


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## Ed Seeley (15 Mar 2013)

In cardinals (and many other small tetras) in the wild they are effectively annuals living, growing and breeding in just one year before dying / getting eaten.  Unless the rate of death is different for each sex or they maintain harems (like Anthias) which tetras don't then there isn't much benefit for switching sex.  Also, in tetras, the largest specimens are female so while it could be dominance suppressing growth of females they aren't switching sex.

AFAIK the only freshwater species proven to have switched sex are a couple of rare South American cichlids and possibly swordtails/platies (but they seem to be non-reproductively functional females showing male characteristics).


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## Tim Harrison (15 Mar 2013)

Just fat then!


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## Nick_593 (15 Mar 2013)

Ed Seeley said:


> In cardinals (and many other small tetras) in the wild they are effectively annuals living, growing and breeding in just one year before dying / getting eaten. Unless the rate of death is different for each sex or they maintain harems (like Anthias) which tetras don't then there isn't much benefit for switching sex. Also, in tetras, the largest specimens are female so while it could be dominance suppressing growth of females they aren't switching sex.
> 
> AFAIK the only freshwater species proven to have switched sex are a couple of rare South American cichlids and possibly swordtails/platies (but they seem to be non-reproductively functional females showing male characteristics).


 

That's cleared up that observation then. Must be a greedy female, and some sort of dominance related growth/ feeding rate, as suggested.

I was just staring into my tank earlier and thought, could it be possible?.. guess not.

Cheers¬!


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## thelats1981 (15 Mar 2013)

put your ear next to the tank - if you hear "you spin me right round baby, right round" you could be on to something!


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## Nick_593 (16 Mar 2013)

Ed Seeley said:


> In cardinals (and many other small tetras) in the wild they are effectively annuals living, growing and breeding in just one year before dying / getting eaten. Unless the rate of death is different for each sex or they maintain harems (like Anthias) which tetras don't then there isn't much benefit for switching sex. Also, in tetras, the largest specimens are female so while it could be dominance suppressing growth of females they aren't switching sex.
> 
> AFAIK the only freshwater species proven to have switched sex are a couple of rare South American cichlids and possibly swordtails/platies (but they seem to be non-reproductively functional females showing male characteristics).


 

Hi Ed, thanks for clearing that up, and it seems you know quite a bit about this subject!.

Just wondering if you could clear this up also? I have five Ram Cichlids' in my tank, and there was supposed to be two males and three females, but sometimes they are a bit difficult to distinguish in the shop as their colours aren't too great (and it seems the grade in Rams has gone down over the past few years, maybe due to selling the not so good cross breeds?).

Anyway, now their in my tank, there are obviously two males and two females. But the fifth one wasn't certain in the shop because of its colour, and could have been a male or female (not sure!). Now it has developed even more of a neutral colouration.
Albeit this could be due to environmental factors from competition between the other inhabitants for food/ dominance, similar to the Tetras?

But my questions is, do you know whether subordinate male new world Cichlids' (in particular, Rams) mimic a female morph to adopt a 'sneaking tactic' to reproduce when larger males out compete them (as they do in Blue gilled sunfish- another version of alternative mating strategies)? With reference to this paper; Alternative male life histories in bluegill sunfish


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## Ed Seeley (18 Mar 2013)

Almost all subdominant male cichlids Will colour down and adopt female / juvenile colouration giving the clear signal that they aren't competing for territory. In a species that pairs up like rams an odd fish, male or female, possible.ur down so that the pairs ignore it as much as possible.

In apistogramma you do also get sneaker males that mimic females, however I've never heard of them in captivity as we don't keep such large groups so there isn't the same pressure on males to adopt different reproductive strategies.


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## sanj (19 Mar 2013)

Ed Seeley said:


> (but they seem to be non-reproductively functional females showing male characteristics).


 
Ah yes, reminds me of pre-op transexuals.

Hormones!


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## Tim Harrison (19 Mar 2013)

sanj said:


> Ah yes, reminds me of pre-op transexuals.
> 
> Hormones!


 
Wrong forum


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