I work in a facility that keeps ~2-3000 fish. I have tried setting my fish up for breeding (transgenic lines, and also wildtype lines) with the classic partitioned breeding tanks, and I do get eggs, but I have to wait and wait for the eggs (they usually will go through the spawning process mostly around noon to 2 pm).
Here's my basic protocol:
The day before set up breeding tanks with male and female separated by the divider, using system water. (I always feed a few minutes before setting them up so that they will get a meal before going into the tanks). I set up a minimum of 10 tanks, because they won't all spawn.
First thing in the morning the dividers are removed, and fish are supposed to get excited and go through the chasing/laying/fertilizing steps, but my fish are too lazy for that. More often I see the females chasing the males in the early morning. Fish get fed flake food at this point (usually they would get artemia but for cleanliness in the breeding tanks they get flakes). They love eating and dash all over the place feeding.
Then I leave them alone, frustrated that they aren't spawning, and hope a few tanks will figure out how to breed. If I go check them around 2-3 pm, I have eggs! I can get pretty typical yields, and the survival rates are normal. They are typically at the 8-16 cell stage when I collect them, indicating they are less than 2 hpf.
For just maintaing colonies this is fine, but if I want to make transgenic fish getting timed embryos will be a pain.
But, why are my fish doing this? It just doesn't make any sense, they breed well (as long you are willing to wait), they number of eggs, and number reaching adulthood are good, the fish in the system are lively, healthy looking fish, we have day/night cycle timers. I just don't understand why my fish are like this. And other people in the same facility aren't having this issue, it's just my fish.
Thanks in advance for insights,