To Cull Or Not To Cull

[smmetz]

About a year ago I took a pregnant platy and put her in her own 10 gallon tank, then removed her after she had her batch of fry. I got about 60 fry from her. The first dozen or so that got big I put in my other tanks. As more of them got bigger, I started bringing them to my lfs. Finally, I kept the last 20 or so "runts" Eventually I moved them into my 29 gallon tank. Being the first time I bred any fish, I just had the "want to save them all" mentality.

In case anyone else decides not to cull the runts, I just want to let you know how that has worked out for me. The runts never did get the size of a normal adult platy. Most stayed around 1 inch long (some smaller). It seems like at least once per month one of the runts dies for no apparent reason. Luckily these sick fish have not yet caused an outbreak of disease in the tank. Because of the frequent deaths, I am not comfortable adding new fish to that tank. I am also limited if I want to re-organize my tanks, swap fish around. I just don't want to spread any diseases to other tanks.

Interestingly, most of the "runts" are males in my case. Female platy are larger than males on average, so I guess it makes sense that the smallest fish in the batch were mostly male. I took out the couple remaining females a few months ago. They were a bit smaller than the other females, but at least now I know the runts of the litter wont be breeding.

Anyway, I just wanted to post my experience in case anyone was not sure if they want to cull some of their fry. You might think that they just need more time to get bigger and healthier, but that is not true.

 

[Miss Wiggle]

good topic, would be nice to get a few other people's experiences then maybe pin it in the livebearers section where you get a lot of people with zillions of fry.

 

[Darkstar]

I cull any 'runts' I have immediately.

 

[smmetz]

yes, and that is what is recommended. However, I think many people dismiss that recommendation, especially when it is the first time they have fry. I just wanted to let those people know what to expect if they do not follow that advice.

 

[CFC]

Culling is an essential part of any breeding program, not only to dispose of runts but also to keep numbers down to ammounts that you can sensibly raise. Some fish species spawn hundreds and sometimes even thousands of offspring, to raise that number of fish to sizes that are suitable for sale requires a set up of commercial proportions. The answer is to work out just how many you can honestly grow on and then give yourself a 10-20% margin for premature deaths, so if you only have a couple of 20 gallon tanks for raising the fry in then you can probably only raise about 20 fish per tank so taking the best 50 of the fry and culling the rest gives you the best chance of raising healthy fish.

 

[Tolak]

I tried seperating the runts from an angel spawn long ago, with the same results, slow growth, occasional deaths, and never reaching maximum size. Runts go into the oscar tank.

 

[PRW1988]

I usually just cull the runts as soon as I see signs of sturgling...