Nannostomus mortenthaleri sexing

[TCMontium]

Hello,

I have read a few/lot of websites and book pages about Nannostomus mortenthaleri sexing and have seen some “male and female” photos too. Unfortunately, the information isn’t consistent. On Seriouslyfish website they say males should have white coloration on the dorsal fin, but no other source I could find say this and even the photo of a “pair” on their website shows a “female” with white coloration (not very bright, but still, it is there) and in Mergus Aquarien Atlas Vol. 6 it is said that the white coloration on the fins is not a way of identifying the sex of tis species.
Other sources mostly say that females don’t have much intense red coloration and that the females tend to have a less rounded, more pointy/sharp edged/tipped anal fin, just like N. marginatus and beckfordi, but much less obvious. The problem with those is, that they don’t show any actual proof with photos and when they do show “female” photos, they could just be non-dominant males.

In Mergus Aquarien Atlas Vol. 6, it is said that the females have a truly black main/middle lateral line, while males have a blue-glow on the main/middle lateral line. Again, their “female” photos contradict with that statement. The photo of the second “female” example has a very intense blue glow to “her” main/middle lateral line. Also both photos of “females” in this book has very intense red coloration to them and their anal fins are perfectly round. Does that mean females can be intensly red colored and can have rounded anal fins? Or are they just all males?

I have found this website. It shows that the male N. marginatus and N. rubrocaudatus have much wider anal fin rays than the females do. Maybe N. mortenthaleri also has this difference between males and females? Does anyone know if they do?

http://aquaria2.ru/node/5938

I have seen N. mortenthaleri fry and egg photos and even a member in this forum said that they bred the species and shared fry photos! Did you ever see or hear about sexing from such breeders? Or have seen photos of “actual females that lay eggs”?

 

[Mike Wise]

I prefer to buy pencilfish in lots of 6 - 12 specimens. This might be unrealistic or the more expensive species like N. mortenthaleri. In this case I'd go with color (deeper in males), body shape (heavier in females) and shape of the anal fin (triangular in females and a rounded tip on males of most species).

 

[TCMontium]

I prefer to buy pencilfish in lots of 6 - 12 specimens. This might be unrealistic or the more expensive species like N. mortenthaleri. In this case I'd go with color (deeper in males), body shape (heavier in females) and shape of the anal fin (triangular in females and a rounded tip on males of most species).

I would do so if the species did not have any sexual dimorphism or the fish wasn’t old enough to sex, but with mortenthaleri the real problem is not the money, but the absurd sex ratio of the sold fish. Almost all specimens sold in stores seem to be males and breeding reports are presumable therefore very very rare in hobby.
I think if I buy 10 fish, the possibility of all of them being male is more than 50%, I would guess maybe 80%. A forum member (I think it was the same one that shared fry photos) mentioned most females dying on the way from being caught to coming to the local fish seller, or even before they reach to the local fish sellers. Mostly males survive the journey, so mostly males are sold in stores. (of course, I do not know if this information is true)

 

[TCMontium]

Also, body shape seems to be uniform in all fish. Anal fin shape seems to also vary in males, I see very intensely colored fish with nearly sharp/pointy anal fins, not perfectly round like some other specimens. Coloration also does not seem to help, since some specimens I have seen with perfectly round anal fins have barely any red coloration.
I do not know if the 10 specimens I have seen live with my own eyes (and a magnifying glass!), or the specimens on the internet and books are all males or if there are some females or if there are MANY females. So I can’t say that these fish are “males with female characteristics”, but I am trying to say that all these info contradicts. There are non-round anal fins with intense red coloration, dull colored fish with round anals, deep bodied fish with intense coloration and round anals etc.

 

[Mike Wise]

I don't think that the females die in transit more than males. It more likely collectors select the more colorful specimens out of the net, thinking they're more valued. Tanks of mortenthaleri and rubrocaudata that I've seen in exporters in Iquitos do have more males but it's more like 2:1. If the fish are young/small then they aren't fully mature and sexing specimens isn't easy. I am usually able to sex them by the anal fin - if at a reasonable size and have 8+ specimens for comparison. Then again, my thesis advisor said I had a 'taxonomist's eye'.

 

[TCMontium]

I don't think that the females die in transit more than males. It more likely collectors select the more colorful specimens out of the net, thinking they're more valued. Tanks of mortenthaleri and rubrocaudata that I've seen in exporters in Iquitos do have more males but it's more like 2:1. If the fish are young/small then they aren't fully mature and sexing specimens isn't easy. I am usually able to sex them by the anal fin - if at a reasonable size and have 8+ specimens for comparison. Then again, my thesis advisor said I had a 'taxonomist's eye'.

The 10 fish I can buy here are seven 4 cm fish and three 3-3,5 cm fish. So, they are adults and sub-adults. None of them are as intensely colored as most pictures on the internet, but some have darker and bigger red colored areas. Are you suggesting that even if all the fish are of similar coloration and body shape, I should look at the roundness of the anal fin as the main sexing method? If that is the case, there might be 5-6 females out of 10 fish I can buy here.
Would you be able to sex fish with anal fin close-up shots and whole body shots Mike? I can take “proper” pictures.

 

[TCMontium]

https://www.aqualog.de/blog/geschlechtsunterschiede-bei-nannostomus-mortenthaleri/

The photos of “young females” in this site shows fish with thin anal fin rays and a more sharp/pointy anal fins, while the “males” show widened anal fin rays and more rounded anal fins. But the photos of “female in male coloration” and “two females” confuse me. In those photos, the male-like females have more rounded anal fins, sadly in both photos the anal fin rays of the male-like females are not in focus to see if they are really thin like in the other “female” photos.
Also the “fully grown female” seems to have somewhat wider anal fin rays than the “young females”, so does that mean the anal fin rays can widen with age, or that “fully grown female” is actually a male? (actually, “her“ anal fin is pointy/sharp too, so I guess the rays do widen, or it just seems wider to me but they are actually realatively thin?..)
Also this website too says, and somewhat proves with photos, that the females lack the white coloration on the dorsal fin that the males very visibly possess. Is Mergus Aquarien Atlas Vol. 6 wrong about this “white fin“ method being false? Do all mortenthaleri females lack white coloration on the dorsal fin or are there maybe some localities/morphs with females that do in fact have white coloration on the dorsal fin?

 

[TCMontium]

As most of the time, I should have searched for videos too. This helps a lot, at least for a locality/morph of the species (if there are any to begin with). The females seem to have easily distinguishable non-round anal fins and little to no white coloration on the dorsal fin. I guess anything with more white on the dorsal fin or rounder anal fin is a male, even if its' general coloration isn't as intense as the established/alpha males, since colors can apparently vary A LOT independent of the sex of the fish. Body shape/round belly also seems to be of no help, even with the females I saw in this and in another video, both were females ready to spawn and yet, the males had deeper bodies than the females or both sexes have exactly the same proportions. At least it looks like that's the case in the videos.

I will still take some pictures and share here just in case I happen to have all adult and young-adult males. I don't trust myself or the consistency of these sexual differences in this species at all, for now.

 

[Bart Hazes]

You can find lots of pictures with indicated sexes here: https://www.aqualog.de/blog/geschlechtsunterschiede-bei-nannostomus-mortenthaleri/
For these images the dorsal fin colouration, white anterior margin, seems to be most indicative.

 

[TCMontium]

You can find lots of pictures with indicated sexes here: https://www.aqualog.de/blog/geschlechtsunterschiede-bei-nannostomus-mortenthaleri/
For these images the dorsal fin colouration, white anterior margin, seems to be most indicative.

Thanks. I linked and talked about this site in a previous post, but I appriciate it.

 

[TCMontium]

Out of the 10 mortenthaleri I have seen here, only 1 fish had no visible white coloration on the dorsal fin. I also looked at the anal fin rays and they seemed quite thin for the brief time period I could observe them with the magnifying glass. The fish looks just like the one labeled as "female in male coloration" in Aquablog's blog entry.
I bought the fish and put "her" in an aquarium with a (presumably) male mortenthaleri and 5 marginatus. Both of the mortenthaleri I have do stretch their fins next to the marginatus sometimes, but not to each other. I don't know if this means both are actually males, but I guess it does.
The other fish at the store are all males, I am pretty sure. They all have white colored dorsal fins and all but 2 smaller ones do stretch their fins to each other. All of their anal fins seem to be the same shape too. Even the 2 smaller fish that act less aggressive didn't have thin anal fin rays or particularly differently shaped anal fins.

If I am not wrong about "If it acts like a competitive male against marginatus, then it is not a female mortenthaleri!", then my mortenthaleri sighting score is: 12 males - 0 females.

 

[TCMontium]

The aforementioned fish that looked like a "female in male coloration" to me, but acted unlike a female, as far as my expectations for a female behavior goes:

 

[TCMontium]

After I think, observe, research and post so much one after another (and probably annoy people with this thread popping up multiple times a day), I found this article, in which not just N. rubrocaudatus is described, but also many important information about other Nannostomus species is given, mainly N. mortenthaleri and N. (cf.?) marginatus.
Apparently when I said "N. marginatus males have much wider anal fin rays than the females do", I was wrong, it is said that not all N. marginatus populations (or possibly subspecies) possess widened anal fin rays. In fact, only males of a Rio Negro population of N. marginatus is stated and showed to possess widened anal fin rays. The article suggests that the males without widened anal fin rays are most likely the males from the Guyana form.
Anyway, the most important information I found in the article is: Males of most known Nannostomus species possess widened anal fin rays, N. mortenthaleri included. This was the information I was looking for. But, a new question came to my mind after learning this: at what age, size or environmental conditions do the anal fin rays of the males start to widen? If the rays widen before they reach 2-3 cm of lenght or before they start to be competitive or before they start to color up, then I must have a female fish. If the rays do widen at a later time, at full body size or at the achievement of dominant social status, than I might just have a male with not-yet-widened anal fin rays.

http://aquadico.com/up/Nannostomus_rubrocaudatus.pdf

Sorry for writing so much and discussing here to myself instead of just thinking for a few days on my own. I acted too early to ask questions without researching properly on my own (well, actually I found this article by chance when I tried to find the x-ray photos again, not really by doing more research, but anyway).