Fish Myths And Weird Facts

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RobRocksFishTank

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RobRocksFishTank said:
 
Male swords can be problematic...  sometimes a male won't develop a tail if there's a more dominant male around.  That is why some people believe that they can change gender... that's just not what happens with them.
 
 
I've seen it happen with a tank full of females. There are even saltwater species that do it. If I remember correctly, some gobies and clown fish are capable of the change. Mother Nature has a way of keeping things going that will baffle the mind.
 
 
 
Byron said:
There are reports of swordtails changing their sex, but to the best of my knowledge there is absolutely no scientific evidence of any actual gender change (in swordtails I mean). If anyone has reliable references to the contrary, please post and I will take a look.  In some cases this may simply be a slower development, but some adult females have been known to develop male characteristics that might be due to infertility.
 
As for distinguishing male/female, the only reliable way is the presence of the gonopodium on males.  This will be more obvious even before the "sword" extension appears or the males begin to get their colouration.
 
Byron.

 
 
 
Rather than hi-jacking a thread, I thought I'd continue this in a new one.
 
I can not provide any good evidence nor do I plan on doing a study to prove that it can happen with swordtails, but I have seen it. Having worked in one of the largest fish departments in the state for many years. I got to see a lot of stuff and hear a lot of stories. I was very aware of the gonopodium and males sometimes not developing swords and females sometimes developing small swords. We had sold the last male of a batch, which happened quite often. I personally checked each female for the presence of a gonopodium but there were nothing but full delta shaped anal fins. A number of days later there was a male in the tank. Can I say with 100% certainty that it wasn't a male? Not really, but I am fairly certain.
 
I've also seen a feeder goldfish that was frozen in ice for an entire winter start swimming after the ice thawed. I would have said that was impossible but it was a good friends fish and I was over there on a regular basis.
 
This post by Rob got my curiosity up. A few google searches led me to an apparently scientific study by J M Essenberg in the 1920s where he/she claims females that had fry then changed to males and fathered additional fry. The scan of the old report is here. Looked fairly legit to me, but I'm no expert. It's a PDF around 14 pages.
 
http://biostor.org/cache/pdf/52/4a/29/524a297e0b3a3a4e25b70f5c93a7b481.pdf
 
That is indeed interesting (after a very cursory scan), thanks for posting the link.  I will delve into this later, as it will be interesting to see if there was any follow-up, the benefit of peer review of scientific papers.  Thanks again.
 
Byron.
 
Maybe this study from 1957 would help http://scholar.google.com/scholar?output=instlink&q=info:jZf8xHOrTN4J:scholar.google.com/&hl=en&as_sdt=0,33&scillfp=11774190582303516603&oi=lle
Here are the conclusions:
 
1. The normal sexual development and differentiation of Xiphophorus hellerii have been observed in the light of the adult sex ratio and the differentiation of the gonads from birth to maturity. The sexual  differentiation has been shown to follow a definite pattern in both sexes. The gonads of both sexes are homologous and indifferent at birth, but within a few days testes and ovaries can be distinguished
by the relative size, number and arrangement of the primordial germ cells. No atypical gonads were discovered in the course of this study which would indicate the possibility of sex-reversal.
2. Injections of testosterone propionate induced spermatogenesis in the ovaries, of immature females but had no comparable effect in mature specimens.
3. Injections of estradiol benzoate induced oogenesis in the testes of immature males but had no comparable effect in mature specimens.
4. Improper initial sex classification and hybrid origin of the fish used are suggested as possible explanations for some of the discrepancies between the results obtained in this study and those reported in earlier investigations.
5. The results of the study of the normal sexual development and the attempts to alter the differentiation pattern by experimental means indicate a stable sexual development and differentiation for this species.
 
And then you find this 1980 study which concluded the opposite, that swords can and do change sex from female to male;
Sex inversion in domesticated strains of the swordtail, Xiphophorus helleri Heckel (Pisces, Osteichthyes)
http://www.tandfonline.com/doi/pdf/10.1080/11250008009440315
 
From the present experiments and those of previous workers, it is possible to assume that in the swordtail, Xiphophoriis helleri, there are gonochoric populations with exceptional (functional and non-functional) sex inversions and populations with a high percentage of protogynous hermaphrodites.
 
Who knows who is right or not here? What I do know is there are not a lot of studies on sex changing in swordtails.
 
Isn't there a saying about experiments and animal behavior that goes something like this, "No matter how controlled the environmental conditions are, the animal is going to do as it damn well pleases."?
 
Thanks TTA for those links.  I read the second in detail, and there are some interesting observations from the author, Elso Lodi.  Assuming I am correctly understanding Dr. Lodi, the sex reversal can only occur in certain individual fish and is not something possible with any specimen.  In other words, certain factors lead to individual fish having the ability.  As with earlier studies, the hybridization of fish in this genus seems to be a key factor.  Wild fish may be less inclined to undergo this, though it is certainly not ruled out.  The excerpt TTA cited is pertinent, and I will continue the citation:
 
From the present experiments and those of previous workers, it is possible to assume that in the swordtail, Xiphophoriis helleri, there are gonochoric populations with exceptional (functional and non-functional) sex inversions and populations with a high percentage of protogynous hermaphrodites. Particularly in the latter the polyfactorial sex determination would cause a wide variability of sexual genotypes (and phenotypes) with different sexual strengths, and thus lead to different balances between the male and the female factors present in each genome. Thus large weak males, of late sexual differentiation, appear along with strong males and females which remain so throughout their life cycle. It may be supposed that some weak females give rise to hermaphrodites or to arrhenoid females; if the transformation of the primary and secondary sex characters occurs at an early stage, animals in functional male phase would arise; if the transformation is late, arrhenoid females would come forth with sterile gonads and atypical copulatory organs. Such problems are open to further investigation.
 
I did a browse of other related articles using Google Scholar, restricting my searches to the most recent works.  These have a benefit in that earlier works have been studied by the current author(s) which makes it easier to see supported or non-supported conclusions.  One study I found interesting solely from the abstract [the complete paper is not accessible for free] which contains this conclusion:
Strikingly, the sex determination region of the platyfish is very instable and frequently undergoes duplications, deletions, and transpositions. This instability might be linked to the high genetic variability affecting sex determination and other sex-linked traits in Xiphophorus. [Molecular Analysis of the Sex-Determining Region of the Platyfish Xiphophorus maculatus, Christina Schultheis, Qingchun Zhou, Alexander Froschauer, Indrajit Nanda, Yvonne Selz, Cornelia Schmidt, Sabine Matschl, Marina Wenning, Anne-Marie Veith, Mariam Naciri, Reinhold Hanel, Ingo Braasch, Agnès Dettai, Astrid Böhne, Catherine Ozouf-Costaz, Stefan Chilmonczyk, Béatrice Ségurens, Arnaud Couloux, Sylvie Bernard-Samain, Michael Schmid, Manfred Schartl, and Jean-Nicolas Volff. Zebrafish. Fall 2006, 3(3): 299-309. 
 
There seems little doubt from the results of the number of studies existing that gender reversal does occur when certain factors are present.  And clearly, we never stop learning, or at least, we must never think we can.  Thanks to those initiating this discussion and providing good sources.
 
Byron.
 
Thanks to whoever edited my post. I didn't realize there would be an issue with that. Where I'm from, that word is accepted by all but the ears of the extremely innocent. I'm truly sorry. It would be appropriate to note that it was moderated, though. I was quoting something and if I had changed the way I remembered it, I would have noted it.
 
Okay, back on to the topic. I think we've beaten the swordtail bit to death but I do appreciate the zealousy in which you guys did your research.
 
How about that frozen fish staying alive in frozen water? I actually saw it in the ice.
 
How about that frozen fish staying alive in frozen water? I actually saw it in the ice.
 
 
I remember asking this question of my science teacher in grade 8, during a science club trip out onto the frozen Lake Erie to observe ice fishing.  His answer was basically no, in the conditions we were at the time experiencing.  The ice was very thick--we were out more than half a mile from shore, and walked among parked cars and pick-up trucks on the frozen ice pack--so it was very cold.  And this seems to be part of the answer, namely, the extent of the "freezing."
 
 Here's an answer [if you can see it, the background seems to be permanent] from a website called A Moment of Science, link:
http://indianapublicmedia.org/amomentofscience/frozen-fish/
 
Can fish and other aquatic creatures really survive in a state of suspended animation until spring? The surprising answer is yes, sometimes. It is true that some fish can spend the winter frozen in ice and come out swimming once the ice melts. Not all fish get caught in the ice, of course. Ponds and lakes freeze from the top down, meaning that beneath the icy surface there is usually a layer of liquid water where fish swim.
But what about fish that are caught in the ice? It stands to reason that the extreme cold would damage the fish’s tissue, effectively killing it. Like all cells, fish cells contain saline, or salt water. Since salt water has a lower freezing point than pure water, even when encased in ice at thirty-two degrees Fahrenheit, cold-water fish are not technically frozen. Moreover, some fish contain a kind of antifreeze substance that allows them to survive very cold conditions.
Much like bears and other hibernating animals, some ice-bound fish are able to shut down basic bodily functions, slow their metabolism, and enter a dormant state. Cold but not frozen, these fish bide their time until spring, when the ice disappears.
 
As to the article, it should be noted that 32 degrees is the freezing point of water. I don't think that there is a limit to how cold ice can actually get, except for extreme temperatures. Maybe?
 
It is possible that what I saw did happen in temperatures mostly near freezing so the anti-freeze/hibernation theory is what I always thought it was. Also, that ice was frozen solid the entire winter. We are only talking about less than ten gallons. The initial freeze was quick. (BTW, I did berate my friend for being so cruel.)
 
I had a similar situation with a Tokay Gecko at a store I worked at. I had just cleaned the ornery little guys cage. As I put him back, he darted right into his water. It just so happens that we had been doing some major water changes and the cold tap water was very cold. As soon as he hit the water, he stopped moving. I freaked. I thought he was dead. I would have been in trouble if it was my fault, so I tried to rememdy the situation before alerting my manager. As I picked him up, I realized that the very cold water could be the cause and hoped that he would recover. It took quite a while and some very careful soaks in progressively warmer water, but he was none the worse for the wear afterwards.
 
RobRocksFishTank said:
Thanks to whoever edited my post. I didn't realize there would be an issue with that. Where I'm from, that word is accepted by all but the ears of the extremely innocent. I'm truly sorry. It would be appropriate to note that it was moderated, though. I was quoting something and if I had changed the way I remembered it, I would have noted it.
 
Okay, back on to the topic. I think we've beaten the swordtail bit to death but I do appreciate the zealousy in which you guys did your research.
 
How about that frozen fish staying alive in frozen water? I actually saw it in the ice.
 
 
Likely the edit you are referring to was completed by the swear filter.  Generally, if a mod needs to edit something for offensive language, then you would receive a PM.
 

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