Fishkeeping

[SueDonim]

From another thread where this was off-topic....

Oh_hunnihunni Wrote:
"You had me intrigued with the gender changing thing, but it seems more likely that apparent sex changes are in fact just late developers, though hermaphrodite fish are occasionally seen. They are usually sterile though, so I think I can just focus on the youngsters who start showing male colouration and separate them out till I can select the best one to go back with the females. "



There are a number of fish that routinely change sex as part of their normal life cycle, eg clown fish, spotties, etc. Here's a general article about it https://www.latrobe.edu.au/news/articles...change-sex.

For guppies, when you do a Google search you get lots of fishkeepers on forums asking the questions related to what they have observed and "experts" coming in saying guppies can't change sex/gender. And you will get an occasional person saying "no, that is wrong" but most of the links they provide are old and gone.

I think the explanation that I have always gone by came from the book Sex, Color, and Mate Choice in Guppies by Houde. I had interloaned the book through my library so don't have it at hand, and Google Books doesn't provide the preview of the right chapter. It was a long time ago (my notes show 2009) so I might be remembering the wrong book. Anyway, what I have always understood is that guppies have XX/XY genes like we do and that when there are no males present (eg in the wild they have been eaten by a predator – they are smaller and more prominently coloured than the females after all) the population can continue by male hormones being triggered in a female so that she can breed with the other females and produce babies. The babies are all XX (ie female) and any that function as male will be less colourful than XY males because many of the guppies' colours are Y-chromosome linked. But it's a temporary survival strategy that helps to prevent extinction until the all-female group gets a chance to meet up with a normal group with access to males again.

It's rarely seen in hobby fishkeepers because no one really keeps groups of females on their own. Usually a tank of sexually mature females will have male fry with them, or already be fertilised by a male from the past (one insemination can last for months worth of broods - the more common "population survival" strategy). So usually when people think they have observed an apparent sex change it is mistaken, but it is occasionally seen. Usually the gravid spot disappears as any developing embryos are reabsorbed, but if the change is late enough in their development a "male" can give birth. Somewhere along the way I have seen a photo of a fish with a gonopodium giving birth.

There are also all sorts of stories about the trade practices in Asia, where most of our imported fish come from, that include a few weeks of use of (reversible) synthetic testosterone to get females to show their genetic colours to facilitate line breeding, and also the practice of somehow manipulating XX-only fish so that the fish bought by the customer are sterile. I have no idea how true that is.

The great thing about your Endlers is that, unless they have been hybridised with guppies, they will be a "pure" population. I have no idea if they can change sex, but surmised that it might be possible because they are so closely related to guppies. Not a worry for you though. You can just sit back and enjoy them so long as you have a means of controlling the numbers, which is what you are doing. Have fun.

[Oh_hunnihunni]

Cryptofertility in Endler livebearers is absolutely fascinating. There was a project in Germany where the researchers put a trio or two in a pond and left them to get on with life undisturbed for two years before checking their genetics. They expected a lot of inbreeding, but found none. From there they went on to discover the females could select sperm packets from specific males to fertilse their eggs, by tagging the packets in a way that allowed the female to give preference to the males they chose over the many opportunistic partners they were forced to encounter. And often, it was not the flamboyant dominant male they chose - the researchers postulating that those males used more energy, and had shorter lives by way of being more attractive to both predation and environmental threats.

I chose Endlers this time round because they are unusual in several ways. They are a fairly recent addition to the international market, being discovered in the 30s and then forgotten until the 70s, and they are a family still being studied in various institutions outside of Venezuela. They are tiny fish, smaller than other guppy species, and different in other ways too, and as you say because they interbreed so readily with other poecilia their types are easily muddied and lost, and new lines created once the breeding stabilises. The tigers I have are probably one of those newer forms, but one of the other interesting things about them is they can throw back to the wild type on rare occasions, something I really hope happens in my tank. A wild form is exactly what I would really like to have, but my search indicates they are present in some South Island aquariums, but not so common in the north.

The gender change thing is fascinating, and some tropical fish definitely have that ability, an evolutionary adaptation to environments where populations can be trapped perhaps, by seasonal rainfall changes. Like the ability to breathe air, or to leap out of one puddle as it dries up, to find another, or to slow metabolism to such a point a fish can survive in the mud layer of a dried up pond, till water returns. But it is a major physical transformation, akin to a caterpillar becoming a butterfly, so I suspect hermaphroditism is more likely. Especially in guppies, which are often inbred in home aquaria, and the results are not always positive. The varieties of form among guppies are truly wondrous, I can see why they are one of the most popular fish.

But oh I so want a wild type Endler! Just one would do! I would give him his own tank and a harem of nubile brides...

[SueDonim]

That would be neat to have! I don't know about the harem of brides though unless they are also wild-type. Regarding guppies I see on iNaturalist that there are some near Reporoa. They might be wild-type but I wonder how they are surviving, unless that stream is warm. I know there are swordtails somewhere around Lake Taupo too, but they have a greater tolerance for cooler temperatures than guppies. Guppies really are tropical which is why I no longer have any - I'm sticking to what can go in the pond and just have White Cloud Mountain minnows with the goldfish. The minnows have no colour variation though, except for the gold version. But at least with the goldfish I have the pleasure of identifiable individuals.

You mention air breathers, of which the main freshwater ones are anabantids. I had thought of getting a paradise fish for the pond but you need the colour of a male, and he would likely eat the minnows - not for food, but out of aggression regarding another colourful fish. I did have some once, and when I put some guppies in it was was extraordinary how quickly the male paradise gulped one down. I won't make that mistake again.

[Oh_hunnihunni]

I do like my gold minnows. They are very active and still young. I suspect they will spawn next Spring. Meantime they are adjusting to the flashy little male Endler livebearers sharing their space, the silver White Clouds are much older and couldn't care less about who is in their water. Having produced a dozen fry I suppose they are well over these young things, lol.

You could try leopard fish, less likely to over run the available space, and a nice contrast to the minnows.

I believe mollies have been found near the hot springs by the motels. If so they arrived well after we left Taupo, I have spent many happy hours in a scooped dip down there and often fished out cooked fingerlings, but not mollies as far as I know!

[SueDonim]

Leopardfish are a good suggestion. Thanks for that. They would probably tolerate our winter cold, and it would be easy to put a few in a big jar over the winter to be sure. I used to do that with the minnows until I realised they are fine outside all year.

I checked for mollies on iNat and there is a recent sighting at Tokaanu. Then I also remembered danios, which are also a bit cold tolerant but not enough. I previously tried danios in the pond but lost them. And used to have fancy mollies in the tropical tank but our water is far too soft for them. It's even not great for guppies which is one reason why I moved from guppies to angels. Angels love our soft and slightly acidic water.