Platy fry

[saiwong]

When you have a large batch of fry, you will always find a portion die for various reasons (e.g. birth defects etc...) which I was expecting.

I have been counting the Platy fry each day and noticed the number going down. Since the Platy fry share the same hatchery as Guppy fry, I initially through it might be the Guppy fry (who were just a few days older) eating the new Platy fry, so I relocated the guppy fry into another container. However, the count of fry kept going down ????

The odd thing is that I never saw any dead Platy fry bodies at the bottom of the hatchery. So what is happening ? Are the fry getting eaten by other fry ? Could the Platy fry be jumping out the hatchery into the main aquarium and getting eaten by the adults ?

[black ghost]

Nature is a wonderful thing. The bioload of a body of water will always level out to what that body of water can support. Someone did an experiment on this with guppies, adding different numbers to different tanks, from a pair to a hundred. The tanks were all the same size and maintained exactly the same, and every tank ended up with the same number of guppies (about 50).

If your fry are in one of those little plastic breeding boxes, they don’t support much of a bioload.

As for where they go, that’s a mystery. I’ve had cichlids breed and left the young with the parents till they’re 4-5”. From hundreds of fry to 30ish. Their numbers are reducing all the time as they grow, but you never see a body. They just seem to disappear.

[saiwong]

Regarding the breeding box, the one I ordered arrived in the post yesterday.
Was a little disappointed that when I opened it, it was about half the size that I expected.

However, I moved the Platy fry into the breeding box. Since it has clear sides (rather than being netted like the hatchery) I could clearly see the fry. All the Platy fry had full bellies (so that is good that I know they are all eating) apart from 1. This fry has crawling at the bottom. When it tried to swim up, it failed and fell back to the bottom. So I believe it sadly had a birth defect swim bladder issue and I don't think it will survive for long.

What surprised me is when the Platy fry were in their original hatchery, most of the time they were stationary and didn't move much. However, once they were moved into the smaller breeding box they became very active and moved around freely. I suspect that since the Platy fry were all close together, maybe safety in numbers gave them courage and confidence to feel safe and explore.

[saiwong]

Update:

I separated the platy fry into groups of 15+ into two breeding boxes. However, after several days the fry were getting bigger so I
decided to move them back to the large hatchery so they could continue to grow.

However, when I came downstairs this morning and examined the fry, there seemed to be much smaller number.
Also the adult fish were seem nibbling at the hatchery netting.

I moved the fry back to the breeding boxes and did some research.
Seems from several YouTube videos that adult fish could eat the fry via sucking them through the hatchery netting !!!
I didn't think that was possible. The fry were ok in the hatchery and the holes where too small for them to escape through on
their own. However, I do understand that it might be possible for adult fish to suck the fry through the netting if close enough.
What do you think, is this possible & the reason why I have less fry ?

[plankton]

I would have said exactly that if you hadn't found it out elsewhere.

[saiwong]

In general I've always found it much easier to raise Guppy fry. I hardly got any guppy fry deaths and they grow quickly.
However, its not the case for other types of fish. When I previously kept fish 40+ years ago I would have much more fry death of Molly & Platy fry.
They would live in the same fry tank as the guppy's. But the guppy fry would continue to live whilst Molly and Platy fry would randomly die for unknown reasons. All the fry were living in ....

the same tank, same water

so why do some fry survive and thrive whilst others die ?

With my current situation today I have some guppy fry and platy fry. Although the guppy fry were born about 7-10 days before the platy fry,
the guppy fry have grown well and are now 3-4 times LARGER than the Platy fry. The Platy fry have hardly grown at all. Why is this ?

[Vale!]

It's very possible that hormones are majorly involved in this.

I did try to learn about it (quite some time ago) but kind of gave up as it's so very complicated. You could do some research and report back?

Terms to use (that I can remember) : growth hormone ; growth limiting hormone ; growth inhibitory hormone ; somastatin (I think - I'm sure there's a better one beginning with 'soma' that I can't recall at the moment) ; growth exocrines (not endocrines) ; allelopathy. If you're researching in an academic source, use 'teleosts' rather than 'fish' ; and use the binomial (Latin) name for the species you're looking at

Hope that helps.

[black ghost]

I’ve never known any livebearer species to be prone to ‘fry failure’. Maybe the platies and mollies are much weaker these days (40 more years of inbreeding since I kept them). Or maybe the growth inhibitors from the guppies are strong. Are you giving them big water changes?

[saiwong]

Yes I do regular water changes. But if it is the water wouldn't the guppy fry also be affected ? Maybe you are correct that it may be inbreeding causing fry to have weaker immune system. Maybe as a test I will buy different male molly from another store to breed with female and see if they produce stronger fry.

[black ghost]

Yes I do regular water changes. But if it is the water wouldn't the guppy fry also be affected ?

Probably buy not necessarily. But I mentioned the guppy growth inhibitors as a possible explanation for the others not growing. But that also seems unlikely or it would be a known thing.
You’d need to buy a wild caught molly for it not to be inbred.