Sexual receptivity! is it all about hormones

[gwand]

As a retired neuroendocrinologist I was delighted to read this article. Could it be as simple as hormones? Probably not. But maybe!

https://phys.org/news/2026-01-neural-progesterone-receptors-link-ovulation.html

 

[Back in the fold]

This is straying into a funny little zone .

 

[GaryE]

When you breed killifish (Aphyosemions) for many generations, you see very set patterns for when they lay their eggs. It can vary within species (morning or evening), but not individuals. I have had mostly females that would only lay eggs early in the morning (discovered as I checked mops for eggs at various times of the day and realized they were predictable in tank one but not in tank two).

I've spent (and seemingly wasted) time trying to figure out if it was lighting, tank placement, etc, and found nothing influenced the time of egg production. Figuring that out matters, because most Aphyosemions produce a few eggs daily, and many eat their eggs if you don't catch on. You want to be able to remove the eggs for incubation apart, with some species. Other never eat their eggs.

This explains a lot - something suspected but not understood. My killies breed like Medakas, who used to be considered as killies by the hobby. A few eggs a day can be boredom snacks or another generation of beautiful fish. I like the latter to happen.

The article suggest I can't influence timing, and I just have to adapt to it, and observe more closely. That's fair. Hormones rule.

 

[Rusty_Shackleford]

The article suggest I can't influence timing, and I just have to adapt to it, and observe more closely. That's fair. Hormones rule.

But we can influence timing in this case.
In the paper the author stated that ovulation occurred around two hours before lights on and sexual activity occurred 1.5 to 1 hours before lights on. We do have control over lighting. While certainly this pattern doesn't hold true in all fish but maybe there are patterns in our fish we aren't seeing because we haven't been looking? It certainly highlights the benefits of a consistent photoperiod and having your lights on timers.

 

[gwand]

By stimulating the hypothalamic pituitary gonadal (HPG) axis or administrating progesterone at the right time and right dose you can take over the process. I use to do this with female rats. If I gave testosterone to a female pup they would display male copulatory behavior as an adult.

 

[GaryE]

This sounds like a Russian discus breeder I knew who thought I was an idiot because I wouldn't use a hypodermic to mass produce difficult dwarf Cichlids...

 

[gwand]

This sounds like a Russian discus breeder I knew who thought I was an idiot because I wouldn't use a hypodermic to mass produce difficult dwarf Cichlids...

These are natural hormones.