My guppy gave birth 4 times previously and each time I recorded the number of fry. The numbers of fry were: 13, 20, 8, 14.

I actually witnessed the birth of the fry this time and noticed a lot of dead fry. There were 3 fry that survived, much lower than previous times, and approximately 8-10 fry that were born dead.

I am not sure how many fry were born dead previous times but as I did not witness these but I'm assuming it was much lower due to the number that survived.

Is there a reason for this decline in fry / increase in fry mortality?

The only changes since previous times is that I have added a small amount of fertiliser for the plants, added a betta fish (although he doesn't seem too aggressive towards the guppy), and the first lot of fry are now at the stage where they try and impregnate the guppy in question (their mother) even though she is already pregnant.

Also, I am based in the UK and the last week or two we have had a lot of hot weather which raised the temperature in my tanks to approximately 31C (87.9F) which may be a little high for guppies however all my other guppies seem to be fine.

  • Of many batches of guppies, swords, platies, mollies , never saw dead at birth; Although mollies will release fry too soon that are unable to swim. Likely a problem with the water ; the first thing I would check is pH. Temperature ? Aeration ? Commented Jul 26, 2021 at 14:21
  • @blacksmith37 ah the temperature has been quite high in the UK recently - I will add that into my question.
    – Jsk
    Commented Jul 26, 2021 at 14:24
  • 2
    The high temperature by itself is not that bad, but it lowers the dissolved oxygen to very low levels. That could be the problem so aeration would help. I have an aquarium on the deck that reaches 32C but the only fish in it are paradise fish which can breath air. Otherwise my pond reaches 31 C , no problem for Koi and giant danios ( from eggs to big adults) with aeration. In previous years the pond has had swordtails and mollies. Commented Jul 26, 2021 at 20:20


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