What to do with runts?

How big are the runts? Are we talking the size of an endler or a guppy? larger?
I have a guppy, endler, shrimp tank that will eventually be overrun (started with 5 guppies and 2 endlers. I have a boat load of fry in there living in the plants. I expected that though).
Depending on your location the temperament and size of the Platys I might be able to take them if needed. I only worry about them eating the adult and baby shrimp like crazy, I figure if they are extremely small then they wouldn't be a problem. I doubt they would breed as most fish that are really small for their type are unable to breed or don't produce living offspring.

It could be a crowding thing, I had molly fry that would stay small (8 months old) and as soon as they got moved out into something bigger they shot up to full size. That is what my friend I gave them to said happened anyway. I should note that food was not an issue for them, I made sure that all my fish were getting fed and fry got twice a day or more for feeding. It was only a few fry that did that, never quite figured out why.

I am willing to bet that they will live perfectly healthy happy lives, maybe a little shorter than normal but not too bad. My runts never seemed to have issues other than no offspring (had a 1-1.5yr old female runt molly never had fry or showed any signs of it).

I'm ashamed I never considered the overcrowding. I did keep 20 in each ten gallon.

And before anyone judges me, these tanks are phenomenal, granted overcrowding is overcrowding but they are heavily planted and the resulting co2 produced is maintaining demanding plants without co2 injection. I maintained the tanks appropriately. I sold about two dozen as soon as they were big enough so they now have much more room, about ten in both tanks. I believe that in my circumstances, for the short time, it was fine, they were healthy and happy. (Knock on wood, I've NEVER experienced fish disease or anything as long as I've had tanks. amazing)

Come to think of it, I THINK I noticed a slight increase in growth since I sold those other fish, the overcrowding may have hindered the already stunted growth!

The small one is maybe like a tetra? The tail is rather large for his body, I can get a better picture tomorrow before I leave for "vacation."



Even the runts are nippy, I'd imagine they would murder shrimp if small enough


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Nordic said:

Always keep separating the young by size. There is a belief that the larger fish produce hormones or something similar that stops the smaller fish from growing.
Also, filters need to be kept really clean to keep nitrate levels down, as this is also a major obstacle to growth. Fish from this family can actually catch up a bit of growth when put in optimal environment.

I use 12 gallon tanks for smaller juveniles, and you really hit a glass wall at about 16 young fish in that volume.

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Thank you for your input! I'm kind of starting to feel bad that I ignored these issues. I thought I was doing everything I could maintenance wise and I thought I was doing phenomenally under the circumstances, and because of my extra attention, I thought my only issue was physical overcrowding. I believe I've kept the tanks rather clean with almost weekly (very gentle) filter cleanings, along with 2-4 gallon water changes, twice a week, or a larger one once a week) during my busy weeks at school. I even occasionally vacuumed the sand tank and the gravel tank, something I don't normally do often or very extensively. I just felt that these extra steps would at least alleviate some of these issues as a short term solution. I think both of you may have nailed the main problems, as I've said I noticed a growth spurt since I sold the other fish.

1.) What would be a fair nitrate level for young growing platys? My nitrates were unbelievably around 10 per API. Should it be closer to null? And everything stayed rather consistent(though I have doubts about my API kit sometimes,) throughout this whole ordeal.

I did do my best to keep the bigger in one tank, and smaller in the other ( for my own OCD) , but boy do they vary in size and difficult to catch in heavily planted tanks.
I will probably give/sell even more tomorrow! There are 10,11 maybe 15? In the tank with the larger ones. Out of chance, the tank with the runts have 9 in it so maybe that's good, I can get it to maybe 7 or 8 per tank tomorrow. Many of them, even the healthy growing ones are still borderline too small to sell.

Thanks again.


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Nitrate is the enemy of a fish grower. Having high nitrates is more detrimental to growth than feeding shortcomings.
Part of why I do not really like gravel tanks is that they are huge nitrate sinks. All the empty space between grains being taken up by mulm over time.
It's ok with a few large fish and some plants, but not ideal for fry. (personal opinion).

What I use for some of my juvenile tanks are those square plastic breeding mats. It provides lots of surface area for biofilm to grow on and the fish just seem healthier for it, also the water stays clear longer (hazy water normally indicates elevated ammonia).
You stick a rock on it to keep it on the floor and just let it float around while you suck out the poop underneath it.

If you are serious about the breeding part, I'd keep something like an oscar that will feed on runts. That way you breed the fast growers. (Don't do this with swordtails, the fast growers never reach the size of the normal ones, it is just a reproductive strategy).

You can just mark them as juveniles or runts in a locals add, lots of people have a predisposition towards things like that.

Well I kept it at 10 or less with frequent ~25% WC's I guess I needed to shoot for zero. All in all, most of them were healthy, and the few runts "seemed" perfectly healthy...well besides the stunted growth.
I'm aware water changes were key, and although I probably could have done more, I think I did relatively well in the water quality area. I did wish that I knew I needed zero nitrates, I feel so dumb, that's probably common sense/common knowledge.

At this point, I want to focus on their continued development. I am particularly worried about the mental health of them, especially the tiny guy, who is rather...'slow.' He is clearly not very intelligent, though he knows when I'm going to feed, and he gets his fair share of food, etc. he isn't as social as the other fish are, he looks like the guy who tries so hard to fit in, but just gets ignoredHaha. He is definitely not one of the guys and I know that can have dampening effects. (Also, note: the males show no obvious aggression yet)

I think I can get nitrates down to zero in both tanks. The gravel tank believe it or not, has always had pristine water. It's always done so much better than my other tanks. Of course that's my auxiliary tank .The ones in the gravel tank seem to be of healthy size assuming they are not from the original batches of fry of course. I will dwindle their numbers today via rehoming. Unfortunately I'll be gone over the holiday, so I'll do as big of a water change as I feel comfortable with, maybe 40%? I'll keep the few runts by themselves (maybe 5 or 6?) and hopefully that will help some. I probably won't get the nitrates down until I'm back home. Any suggestions there?


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Nordic said:

Doing water changes much smaller than 50% is not worth the work...

There is a post somewhere on the site where someone ran the numbers.

Click to expand...

I will have to respectfully disagree there. For now. Haha. I'll search for the thread but I'm terrible with forums so I'll probably have no luck. I'm very interested in these "numbers" as I'm very skeptical of this claim. 25% changes 2 or 3 times a week (for my purposes,) seems rather practical and effective, and a good approach for the frequent water change people. (I understand how doing frequent changes removes less "stuff" due to dilution, adding clean water and then the next change will remove less "stuff," to put it simply, I get that, but if you do enough consistently, then I feel it would be just as good depending on the circumstances, it also prevents larger swings in water parameters.). I guess it's just worth the extra work FOR ME. Can you elaborate on anything else regarding this claim? Or is this based on the post you speak of?
I don't mean to be rude, I know you have a lot of valuable experience and knowledge (more than me! Haha) and I have a lot of respect for you, I feel you're a valuable member of the forum. Thanks again.


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