Mosquito Fish Breeding against the odds. Seriously. Bizarre!

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Aquarium Advice Addict
May 1, 2011
Tacoma, WA
For starters, I know the odds are usually FOR livebearers breeding prolifically. However, in this case, it's actually quite stunning.
I had two leftover Mosquito Fish (Gambusia Affinis) after placing some in a customer's pond for bug control. One male, one female. The female died giving birth to a single fry. A male.
This left me with two males. There goes my breeding program, right?
Watched this little guy grow up, develop his gonopodium, and wander the heavy growth of plants in the tank. I intended to buy more fish later, but the $35 minimum order from livequaria irked me.
So I left the two male fish alone with a crayfish and some American Flagfish. And then the other day, looked closer......
One of the male moquito fish has lost his gonopodium in favor of a triangular anal fin and a gravid spot.
I have not been able to find any information about Gambusia spontaneously switching genders. Anyone else seen this?
This is very normal, any fish when they do not sense the presence of a female or a male for that matter have the ability to change their sex in order to reproduce. It is not the most common event, but definitely not unheard of.
Not all fish possess that ability. In fact, as I understand it, very few species (in the grand scheme of things) do.
But, fun fish facts!
There is a type of Molly native to South America that is 100% female. There are no males. They mate with a male of another species, but do not use any genetic material. The mating process simply activates their gestation process. Essentially, they need to get laid to take care of business themselves.
I actually did quite a bit of research on Gambusia fish before posting this, including reading a few papers about their sex chromosomes. Nowhere was there any mention of an ability to change gender. This ability is rare in animals with prominent secondary sex traits (like the gonopodium).
This isn't just seen in a few species, any fish no matter what species can in fact change gender when there is a lack of the opposite sex in the presence, I'm not saying that each individual fish can do this, but each individual species can.
Just to clarify, by fish I mean the stereotypical fish, not like whales or things like that.
Yeah... whales aren't fish at all. So I don't know what you mean by stereotypical fish... except perhaps... "fish"?
And no, not all fish species can change gender. Clownfish, some wrasses, a few other reef fish... not very common in freshwater fish.
Sorry to be nitpicky, but I'm kind of a word nazi. "All" means zero exceptions. As in, every single species of fish, up to and including sharks.
This isn't just seen in a few species, any fish no matter what species can in fact change gender when there is a lack of the opposite sex in the presence, I'm not saying that each individual fish can do this, but each individual species can.
Do you have some documentation that proves this? I've heard anecdotal evidence for it but have never seen any real data.

@ the OP, are you certain that another fish didn't get in there somehow? How large is this pond? I've heard of isolated bodies of water getting fish transferred by birds, storms, floods, or even random people deciding to be charitable.
From Wikipedia (Yes, I know it's not 100% reliable, but you can always check their own sources)
Protandrous hermaphrodites refer to organisms that are born male and at some point in their lifespan change sex to female. Protandrous animals include clownfish.
......... (then on down to Protogynous, or female to male) .............
In the following fish families: Serranidae (groupers),[10][11][12] Sparidae (porgies), Synbranchidae (swamp eels),[13] Labridae (wrasses), Scaridae (parrotfishes), Pomacanthidae (angelfishes), Gobiidae (gobies), Lethrinidae (emperors), and possibly others.[14]

Seems like a lot, until you consider the thousands of species of fish.
And Jetajockey, it is a twenty gallon aquarium in my bedroom. But you're right about fish being introduced in strange ways! I had another customer return from a weekend trip to find 100 (not kidding, I counted when removing them) goldfish in their pond.
Oh okay, I was under the impression that they were still in the pond. That's really interesting, it'd be nice to get some more information on it for sure, as this isn't the only time I've heard of it happening.

As far as the list of hermaphrodites goes, I'm aware of most of those, I was asking about BuckSh0t's claim that any fish species can do this.
By all I did not mean literally all, by stereotypical I meant freshwater mainly, and in my own fish tank I had a guppy change gender it isn't that rare of an event, I've had experience and I've done research, of coarse not every single species of fish can do this but most can, mainly freshwater fish are known for it though
I may not have phrased it clearly in the original post. I bought about 13, gave 11 to the customer, kept 2 (1 male, one female). Female died giving birth to a single male fry, which grew up, lived there for about 4 months.. then spontaneously changed gender.
I was aware that a few fish could do it, though I didn't realize how many until recently. I posted the list of fish families primarily for anyone who is reading the thread who doesn't know much about the topic.
I've been scouring the net for any information on livebearers changing gender, and I've found extremely little on the topic, and nothing specifically about Mosquito Fish.
Thanks for telling me about your guppy! They're pretty closely related. From what I've been reading, it actually is very rare, so you got to witness something very unique! Did it go female to male, or male to female?

I think it's actually more common in saltwater fish than freshwater, at least from what I've been reading. If you know of any good papers on the topic, I'd be interested!
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