slowed egg development

[CT_]

I collected some medaka eggs starting 20 days ago.  they're in methylene blue 3ppm.  last time they hatched under the same conditions in 10 days.  this time none of hatched.  They are eyed up and under the microscope the few I've picked out have heart beats and will wiggle like normal occasionally.

I know cold can delay medaka by quite some time but the room they're in is always 20C-25C.  Its in my office so sometimes the room gets up to 27-28C if my computer is working hard.

 

Does anyone know conditions that would slow development other than temperature?

[modified lung]

I've noticed my medaka eggs getting full sun in the window have about 10 day incubation periods and high hatch rates. Partial sun still have high hatch but take 14+ days. No sun seem to get very low hatch rates.

I haven't done anything like structured trials though so I can't say for certain.

[CT_]

Hmmm.  last time was summer and it was by the window.  They do get very bright lamp light whenever I'm around, but its not consistent.  Last time was 100% hatch rate (excluding the unfertilized ones i removed early)

[Minanora]

I was going to mention light as well. It's amazing what that can do to growth/hatch rates.

[CT_]

an update: one hatched out Tuesday night (odd just one) and then another 4 this afternoon.  so strange it took them this long but I'm happy to see they eventually did hatch.