Black Neon Tetra Gender Differences?

[Marlintheshark]

I got fish yesterday and as they are my first fish and pets, i was thinking of naming them. I want to be able to know the differences between females and males. Anyone?

 

[Brianandrews1951]

Black neons are not the easiest fish in to tell males from females. (There is no difference in color or finnage - no quick solution here I'm afraid!) It is only possible to identify males from females as they mature sexually, in which case the female becomes larger and plumper than the male, while the male remains small and narrow (viewed from above). There is a fairly good chance that yours are still sexually immature, in which case it will be impossible to tell. It will also make things difficult if both or all of your fish are the same sex, but if they all get large (say 35 mm/1.4 in) and plump, they will all be females. That might take weeks to a few months, depending on their age. Alternatively, if they remain smaller and narrow, they will all be males. Depending to some extent on their life history (that is, living conditions, food etc) they can be expected to start to mature at about 25 to 30 mm (1 to 1.2 inches), though as I say, many things can influence this. Interestingly, the males of many tetras develop what are called Characin hooks in the anal fin (the long, single, hinder fin underneath). These tend to catch on nets, and one immediately knows the fish is a male. As far as I know, no one knows for certain what these hooks are for.
 
Black neons are wonderful, good-natured community fish. I hope yours do well! Good luck with them.

 

[Marlintheshark]

Black neons are not the easiest fish in to tell males from females. (There is no difference in color or finnage - no quick solution here I'm afraid!) It is only possible to identify males from females as they mature sexually, in which case the female becomes larger and plumper than the male, while the male remains small and narrow (viewed from above). There is a fairly good chance that yours are still sexually immature, in which case it will be impossible to tell. It will also make things difficult if both or all of your fish are the same sex, but if they all get large (say 35 mm/1.4 in) and plump, they will all be females. That might take weeks to a few months, depending on their age. Alternatively, if they remain smaller and narrow, they will all be males. Depending to some extent on their life history (that is, living conditions, food etc) they can be expected to start to mature at about 25 to 30 mm (1 to 1.2 inches), though as I say, many things can influence this. Interestingly, the males of many tetras develop what are called Characin hooks in the anal fin (the long, single, hinder fin underneath). These tend to catch on nets, and one immediately knows the fish is a male. As far as I know, no one knows for certain what these hooks are for.
 
Black neons are wonderful, good-natured community fish. I hope yours do well! Good luck with them.

Thanks,
I think I have 4 females and 1 male depending on how you described them. The females seem to have a large lump on the stomachs and the male just looks normal. Is tis right???

Unfortunately 3 of my neon tetras died yesterday (a few hours after their first feeding) and I'm worried about my black neon tetras.

Any help?

 

[Brianandrews1951]

If there is such a clear difference in the black neons, there is a good chance you are right with the sexes. Fortunately, regardless of the sexes they are very peaceful fish, and all will live happily together. By the way, the way to tell males from females in neon tetras is the same as for black neons, though neons do not grow quite as big.
 
I am really sorry to hear you lost 3 neons. It sounds as though your tank is newly set-up? There are factors - notably to do with this and water chemistry - that can cause trouble, but if the black neons are still behaving well, this is a good sign. Neons can be pretty delicate and stress easily. Even the stress of catching and bagging at the store, bringing them home and introducing them to the new tank can stress them a lot. All has to be done quite carefully, which I am sure you would have been aware of. Sometimes these things happen, no matter how careful we are. I would be surprised if the feeding caused the problem. Did you actually see them feeding?
 
It is especially good if the black neons have started feeding - shows they are settling in and comfortable. However, I would recommend feeding very lightly at first, and make sure the food is all eaten within a minute or two. I would not feed more than twice a day. You are probably aware of this, but uneaten food can easily cause trouble by producing ammonia, especially in a new tank. Ammonia is poisonous, but its production is perfectly natural and normal, and there are ways to deal with it. Have you done anything to prepare the water? By that I mean ageing it and encouraging the development of nitrifying bacteria. These bacteria convert the toxic ammonia, produced mainly by the fish and any uneaten food, to far safer nitrate. They live in all natural water with fish, and are the wonderful way in which nature purifies water and recycles nutrients. Plants feed on the nitrates. In aquariums the bacteria live in the biological filter as well as on other surfaces. (Are you able to test for ammonia? Very important, especially in the early days.) Note that I would certainly not expect ammonia to be the cause of your neons' death so soon after introduction if they were the first fish. 
 
It is safest to under-stock your tank with fish initially, say for a month, before putting a heavier load of fish into it. (I don't know the size of your tank and how many fish you have at present, so can't give guidelines. But it is safer to be cautious until the tank stabilizes and matures.) Hopefully things will settle down now.