Its been a while since I last bred Danios of any sort, but this is an account of how I did it: (this is also the method I used for most Characins and other egg scatterers…i.e. red eye Tetras, Black widows, - mainly all non adhesive egg fish)
pH was not much of a focus area as Danios are reasonably flexible in ranges from 6.8 to around 7.4 and the temperature ranged between 25 & 28 deg C.
Ideally, 3 tanks (24x12x12) produces the best results for mass spawnings … one tank to condition the males, one tank to condition the females and one tank to spawn them in…. (I used 3 tanks because I had them available, but you can get away with using 1 tank with a partition (You can use a glass devider... I normally used an 8mm thick perspex sheet with hundreds of 8mm holes drilled through it to allow some water exchange between the various compartments) between the male and female sides which is removed when you want to spawn them)….I always used two more males than females i.e. 5 males to 3 females, 7 males to 5 females etc.)
At least a week before the spawning date, Id separate the males and females and condition them (mainly) on live Daphnia, Newly hatched brine shrimp and bloodworms.
The spawning media may vary from marbles covering the whole base area, to a cluster of thick plants (hornwort or Cabomba) bundled in the darkest corner & weighed down by a small stone. (Plastic spawning mats are also effective).
I find that the best positioning of your aeration is directly in the v of the back panel on the same side where you've clustered your targetted spawning area. A medium flow which visibly circulates the water in this area also seems to stimulate breeding to some extent
Two days before I intend to place males and females together, I would add 4 drops of Liquifry to the spawning tank, so that infusoria can start developing as first foods for the fry when they hatch.
On the evening before the planned spawning event, I would drain the water to around 4 depth, cover the tank (in darkness) if the light cannot be switched off, and set my alarm for sunrise the next morning.
When I remove the covers in the morning (or switch on the light), Id fill the tank to around 8 depth with water at a slightly lower temp than the water in the tank, and remove the partition between males & females, or if more tanks was used, transfer the males to the female tank. Spawning will start immediately and carry on for almost 4 hours.
Observe periodically as one or more fish may be spawned out long before the rest and then start egg hunting and eating them…. If you observe any such culprit, remove them immediately, as they will eat many, many eggs. (your intervention will not stop the spawning activity)
After some time, you will observe that most of them would have no further interest in spawning, (and all indulge in egg-eating) at which time you remove them all to their original quarters.
When all spawners have been removed, syphon water out from the top on the opposite side of your "targetted" spawn area to a depth of 4",- just making sure that none of your spawn receptical protrude above water level - (so that you can just top up 1" of water per day after the fry becomes free swimming and you do not have the risk of syphoning them out when doing water changes during the first week).
During the spawning and hatching process.... only an airstone is necessary in the position I have mentioned.... After freeswimming (which would be on the third day after spawning)... You refill the tank by 1" per day, (having started off at 4"... as stated)...On the 4th day you will then be at 8" and only then, you disconnect your airstone and connect your tubing to a sponge filter. (doing it earlier than that, ... your fry will be sucked up by the sponge filter (or any other filter).
And then…. Congratulations!!!... youve achieved your first spawning…. As easy as that. (the fish will be ready for their next spawning about 8 days later if the same procedure is applied.)
I've Re-editted the above to include some important points on filtration which I ommitted during the first attempt.... (as I said... it's been a long time since I last bred Danios & I may even recall some more issues for inclussion)
