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how does one sex cardinals/neons. i have a few of each and some are fat, where some are slimmer. i am guessing that the fatter ones are females and the thinner are males. also i have them in a 20Gal with some moss, will they breed sooner or later.

When the fish are mature, males will be shorter and slimmer than the females.

They aren't super easy fish to spawn, let alone breed. The eggs and fry are sensitive to light, and do best in darkened aquaria. If you are serious about breeding neon and cardinal tetras, it's best to give them their own breeding setup, condition them, then pick out the best pair of fish and try them out.

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And when he gets to Heaven, to Saint Peter he will tell: "One more Marine reporting, Sir! I've served my time in Hell."

I also recall that they can be sexed via the curvature of the striping, though I'm not sure if there is any truth to that.


Also, spawning is not too terribly hard of an undertaking. I unintentionally bred mine in a 2 wpg tank. Soft water, however, is a must (note that low pH is not mentioned).

Last edited by Cup_of_Lifenoodles at 23-May-2005 23:29

ok i figured they be eaier to breed since there are so many of them, no i am not trying to breed,but j.w since it would be cool if they did.

As is true of most of the smaller characins, the neon, and cardinal males can be distinguished buy the anal fin. A male will have a small hooked curve to the anal fin if you look closely that the female lacks. If size doesn't tell you that its male or female, the hook will.

Last edited by tanker at 27-May-2005 13:16

Neons and Cardinals will spawn fairly readily if the water conditions are correct - they need soft, slightly acidic water for this. I've had my Cardinals spawn once in the Panda Fun Palace™ after a water change. Fortunately my water is naturally soft and slightly acidic, which makes it easy for me to keep South American fishes or other fishes from other biotopes with similar parameters (e.g., certain Asian rainforests).

However, breeding these fishes is a much harder task. As has already been stated above, the eggs are photosensitive, and if breeding is to be attempted, this should be performed in a specially furnished aquarium that can be darkened after spawning. The aquarium should not be lit, and should be furnished with Java Moss (which fortunately will stand the lighting conditions wihtout wilting) to provide the parents with a spawning substrate. After spawning has been observed, the parents should be removed, and the aquarium placed in total darkness (covering with a large towel should do the trick) for 72 hours. Fry are tiny when free swimming, and need infusoria for a minimum of 7 days, possibly as many as 14 days, before they can be introduced to newly hatched Brine Shrimp.

Also, because the water has to be soft and acidic, keeping the fry nursery clean is a challenge. A box filter containing a small quantity of aquarium peat is recommended by some authorities. Set it up so that it is driven by a gentle air current from a small air pump, and leave the lid off to prevent the fry becoming trapped for the first 7 days. Afterwards, the lid can be replaced to improve the filter efficiency.

To bring a good sized clutch of Neons or Cardinals from fry to saleable size will be a serious challenge of the ability of even experienced aquarists. Expect the success rate to be very low at the first attempt, and if any fry do survive to 3 months of age, say, then this will be a considerable feather in one's cap.

I took a peek in my TFH back numbers, which dealt with the Glowlight Tetra, whose fry are difficult to raise because they need very low carbonate hardness for the first 14 days, and gradual introduction to increased KH levels. I suspect that a similar phenomenon may manifest itself among Neon and Cardinal fry. If your tap water is better suited to Rift Lake keeping than Neon/Cardinal breeding, you may have to resort to RO water. The fry requirements are likely to be that stringent.


Panda Catfish fan and keeper/breeder since Christmas 2002

I agree. RO is very important. In attempting to lull my ancistrus into the mood for romance, I did a fifty percent RO swap. This was what initiated the cardinal spawning--funny, as the ancistrus, have, as of now, yet to spawn.