My breeding trio of bristlenose that regularily spawn have had one big spawn (80 or so fry) in the new tank system I designed and then I moved the male to tank by himself so I could fatten the adults up. the babies have all worked there way into the fry tank and seem to be going strong. Now this is the first time ive only had one spawn of fry and been able to watch the results over a month. There is a considerable size difference between the fry with some being fat and large and others being slim and scrawny, does this just attribute to desire to pig out? Also proberly finding on average 2-6 dead fry a week which appear to be the scrawny ones with the fat and middle sized ones seeming to go strong. With these differences in size and mortality rates do you think it would indicate that my trio might be related somehow and causing bad genetics in the fry? Until ive observed fry size ive always just asumed the larger ones where older but these ones are all the same age.

Did you buy your trio at the same LFS or breeder, if so they could well be related.

Different growth rates are not unusual, I've found moving the slower growing ones to another tank has a good effect on their growth rate.

It may be that they are being outcompeted for food.

Survival of the fittest. In the wild the smaller ones get picked off by predators

there are lots of reasons why fry may die. The size they die can often be a key indicator. A bit more detail on the fry migth help