This question is a perpetual thread, recycled over and over again on this forum.
THE URBAN LEGEND: Various versions of this - You can tell by the shape of its head or jaw. You can tell by how thick or how long the body is. You can tell by some aspect of the white stripe. You can tell by the dorsal fin. You can tell by the tail. When asked, people point to a forum post from another site where someone with no scientific credentials describes a questionable set up from an unknown and unpublished source. Also involved in the legend is that BGK are bred in captivity, and you can do it too if you get your hands on a male and a female.
THE FACTS: None of these assertions are true. BGK have no obvious external sexual dimorphic characteristics that a casual fishkeeper can observe in home aquaria. I have read many scientific publications about BGK and all come to the same conclusion. To be absolutely certain, I have corresponded with a university professor who has a PhD and studies knife fish EXCLUSIVELY. He has a lab full of tanks that are full of knife fish. I have personally read 6 articles that he published regarding studies on Apteronotus species, and many of those studies were directly related to sexual characteristics, specifically differences in electrical discharge between males and females of the species.
This is what he said - I am paraphrasing - some species, like BROWN ghost knife fish, are very sexually dimorphic and the sexes are easy to tell apart by external characteristics such as body size, snout shape, and the shape of the urogenital papilla. This is NOT the case with BLACK ghost knife fish. Even the shape of the urogential papilla is not enough to confirm whether the fish is male or female, because it varies among populations. When the researchers in this lab determine the sex of a BGK, they do a laparotomy (surgery), because that is the reliable way to say for certain if the fish is male or female. The other way, which is a bit less reliable, is to measure plasma levels of 11-ketotestosterone and estradiol.
Furthermore, again according to the professor, BROWN ghost knife fish have been successfully bred in captivity by a few individuals, but there is no published account of ANY successful BGK breeding. They have many sexually mature BGK together in the lab tanks and there has never been any spawning.
I do not want to publicly post the name of this contact or the exact copy of the correspondence, as I did not ask for permission, but I would be happy to provide it to a moderator for verification. I have been researching this exact topic for quite some time now, and I have gone to great lengths to be sure all the information was correct before sharing it.
I don't think it is helpful to the forum members for blatant disinformation to be spread about and taken as truth, as is the case of the multiple threads about "How to Sex (Breed) Your BGK." Someone has gone as far as to "lift" other people's pictures off other websites and label them as 'male' or 'female', which is not only untruthful but a copyright violation as well.
I am not blaming the people who received this bad information and believed it. I even let them try to determine the sex of my BGK. (As I recall, it was about 50% male and 50% female, but better pictures were needed.) I just think it's important for everyone to know that you can NOT determine the sex of a BGK by these methods, as I read that people are attempting to do so in the hopes of breeding them in their home aquaria, which would of course be a waste of time, money, and effort, and could end up with the owner arranging a "marriage" that will end in disaster for one or both fish.
Any internet claims of BGK breeding in captivity should be looked upon with the very highest degree of suspicion. Even the most well-known claim of breeding in Australia is totally unverified and at this point must be treated as a rumor at best. As the primary fish species that I keep are native to Australia and New Guinea, I know that Australia has extraordinarily strict laws regarding the export of fish, so I doubt very seriously that an Australian breeder of BGK would hide his or her methods in the hopes of making a profit.
At my house, because I have kids and therefore everything must have a gender and a name, we "determined" the sex of our BGK today with an old-fashioned coin flip. It's a boy! I hope that hearing these facts will allow us to get back to enjoying our BGK without chasing around these silly "fish tales" about sexing and breeding them.
Thanks for reading,
Deana
THE URBAN LEGEND: Various versions of this - You can tell by the shape of its head or jaw. You can tell by how thick or how long the body is. You can tell by some aspect of the white stripe. You can tell by the dorsal fin. You can tell by the tail. When asked, people point to a forum post from another site where someone with no scientific credentials describes a questionable set up from an unknown and unpublished source. Also involved in the legend is that BGK are bred in captivity, and you can do it too if you get your hands on a male and a female.
THE FACTS: None of these assertions are true. BGK have no obvious external sexual dimorphic characteristics that a casual fishkeeper can observe in home aquaria. I have read many scientific publications about BGK and all come to the same conclusion. To be absolutely certain, I have corresponded with a university professor who has a PhD and studies knife fish EXCLUSIVELY. He has a lab full of tanks that are full of knife fish. I have personally read 6 articles that he published regarding studies on Apteronotus species, and many of those studies were directly related to sexual characteristics, specifically differences in electrical discharge between males and females of the species.
This is what he said - I am paraphrasing - some species, like BROWN ghost knife fish, are very sexually dimorphic and the sexes are easy to tell apart by external characteristics such as body size, snout shape, and the shape of the urogenital papilla. This is NOT the case with BLACK ghost knife fish. Even the shape of the urogential papilla is not enough to confirm whether the fish is male or female, because it varies among populations. When the researchers in this lab determine the sex of a BGK, they do a laparotomy (surgery), because that is the reliable way to say for certain if the fish is male or female. The other way, which is a bit less reliable, is to measure plasma levels of 11-ketotestosterone and estradiol.
Furthermore, again according to the professor, BROWN ghost knife fish have been successfully bred in captivity by a few individuals, but there is no published account of ANY successful BGK breeding. They have many sexually mature BGK together in the lab tanks and there has never been any spawning.
I do not want to publicly post the name of this contact or the exact copy of the correspondence, as I did not ask for permission, but I would be happy to provide it to a moderator for verification. I have been researching this exact topic for quite some time now, and I have gone to great lengths to be sure all the information was correct before sharing it.
I don't think it is helpful to the forum members for blatant disinformation to be spread about and taken as truth, as is the case of the multiple threads about "How to Sex (Breed) Your BGK." Someone has gone as far as to "lift" other people's pictures off other websites and label them as 'male' or 'female', which is not only untruthful but a copyright violation as well.
I am not blaming the people who received this bad information and believed it. I even let them try to determine the sex of my BGK. (As I recall, it was about 50% male and 50% female, but better pictures were needed.) I just think it's important for everyone to know that you can NOT determine the sex of a BGK by these methods, as I read that people are attempting to do so in the hopes of breeding them in their home aquaria, which would of course be a waste of time, money, and effort, and could end up with the owner arranging a "marriage" that will end in disaster for one or both fish.
Any internet claims of BGK breeding in captivity should be looked upon with the very highest degree of suspicion. Even the most well-known claim of breeding in Australia is totally unverified and at this point must be treated as a rumor at best. As the primary fish species that I keep are native to Australia and New Guinea, I know that Australia has extraordinarily strict laws regarding the export of fish, so I doubt very seriously that an Australian breeder of BGK would hide his or her methods in the hopes of making a profit.
At my house, because I have kids and therefore everything must have a gender and a name, we "determined" the sex of our BGK today with an old-fashioned coin flip. It's a boy! I hope that hearing these facts will allow us to get back to enjoying our BGK without chasing around these silly "fish tales" about sexing and breeding them.
Thanks for reading,
Deana
) knows what will induce black ghost knife fish to spawn.
