Annual killifish eggs: the storage box temperature decides on diapause
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
When a killifish keeper stores a peat box in a cupboard, they set, without thinking about it, the parameter that will decide the fate of the embryos. Podrabsky, Garrett and Kohl showed in 2010, in the Journal of Experimental Biology, that incubation temperature steers annual killifish eggs onto two very different developmental paths (see the study). Our setup benchmarks sit in the fish bedding and habitat section.
Contents · 5 sections
Three programmed pauses in development
Annual killifish live in temporary pools that dry out every year. Their eggs survive buried in the substrate thanks to an ability rare among vertebrates: suspending their own development. Wourms described it back in 1972 in the Journal of Experimental Zoology, identifying three successive pauses — diapauses I, II and III — of variable duration (see the study). That framework explains why a single spawning can hatch on widely spaced dates. The species concerned are introduced on our dedicated killifish profile.
Twenty-five or thirty degrees: two distinct paths
The team worked on Austrofundulus limnaeus, a South American annual killifish. Incubated at 25 °C, the majority of embryos entered diapause II. Shifting from 25 to 30 °C, by contrast, made every embryo escape diapause and develop straight through. The two paths diverge as early as the segmentation period, with development running ahead in the embryos that escape diapause.
The study also flags a maternal factor: young females produce a higher proportion of diapause-escaping embryos than older females. The same pair, a year apart, will not necessarily behave the same way.
What this changes inside an incubation box
In practice, the temperature of the room where the box sleeps often weighs more than the incubation time on the label. A few benchmarks:
- First establish whether the species is annual: non-annual killifish such as Aphyosemion or Fundulopanchax have no obligatory diapause.
- Record the storage room temperature, not just the tank temperature: that is what the eggs actually experience.
- Be wary of a warm cupboard in summer as much as a cool cellar in winter: those swings are enough to switch scenarios from one spawning to the next.
- Write the collection date and temperature on every box: an incubation that seems “too long” is often a diapause, not dead eggs.
Once hatching happens, everything hinges on the first few days: our guide to hatching brine shrimp at home covers the logistics of that first live food.
What the study does not demonstrate
These results concern a single South American species. The 30 °C threshold does not transfer as is to African Nothobranchius, nor to non-annual killifish. The study measures neither hatching rate, nor fry survival, nor the effect of rewetting: it describes a developmental orientation, not a breeding yield, and says nothing about photoperiod. It explains why two identical boxes behave differently, without supplying a turnkey recipe.
Frequently asked questions
Is a peat box that has not hatched after several months a lost cause?
Not necessarily. In an annual species, a long wait often corresponds to a diapause, whose duration is variable by nature.
Should the incubation box be warmed to speed things up?
The study shows warmer incubation steers embryos out of diapause in the species tested, but without measuring hatching or survival: nothing supports inferring a breeding gain.
Does this result apply to all killifish?
No: it concerns a South American annual killifish. Non-annual species have no obligatory diapause and the thresholds do not transfer from one genus to another. Find all our guides on the fish hub.
See it in the Planète Pets shop: Hang-on isolation and breeding box for aquariums (€28.90) · the whole shop
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.
