Corydoras Fry growing slowly

[Rycraft]

First try raising corydoras fry. I only grabbed around 20 eggs because I wasn't sure how it would go. Had a pretty good hatch rate back in late January 2024. I had 6 that made it to the juvenile size after 90 days or so and that were "tank safe", so I sold them to my LFS as I don't have room for all of them.  The LFS said they were a great size and looked really healthy for reference.

 

I kept the rest that were much smaller as the ones I would keep for myself. A couple have since died and now I only have 3 left. It's now almost four months in and these three are still quite small. Is that normal?  Should I expect this process to take upwards of six months or more?

 

These are Corydoras Aeneus. Being kept in a 10 gallon only 3/4 full so they have easier surface access for air if needed. Had them with a cycled sponge filter from the beginning. There's also some healthy bunches of java fern and some ramshorn snails as a clean up crew. I do water changes twice a week as there are not many in there now and I don't believe water quality has ever been the issue. The ones that died never moved around well and generally didn't look as healthy as the others. 

I'm feeding four times a day. Switching between frozen BBS and rotifers and also adding in crushed up bug bites and flake food to keep variety. 

 

Attached are pics and you can see the one next to an alder cone for some sense of scale. 

[jwcarlson]

I'd guess that it might have been water quality at least at some point.  My understanding is that nitrite poisoning can appear fine in the near term, but have long lasting effects.  

That's a current picture of a 90 day old fry?  

Do you have pictures of them near the ones that you sold to the LFS?

Edited May 16 by jwcarlson

[Rycraft]

On 5/16/2024 at 3:09 PM, jwcarlson said:

I'd guess that it might have been water quality at least at some point.  My understanding is that nitrite poisoning can appear fine in the near term, but have long lasting effects.  

That's a current picture of a 90 day old fry?  

Do you have pictures of them near the ones that you sold to the LFS?

I would be shocked if it was water quality. When they first hatched I was doing water changes every day at first and every other day around the 45 day period onward. Here is a pick of the larger ones that were sold. This is at about 60 days and you can see this one is clearly much larger than the one in the background.  I originally had them in a 6 gallon cube that was bare bottom before moving them to the 10 gallon with sand at around 70 days or so because I felt the 6 gallon was too small with the larger ones getting so much bigger than the others. 

 

Should these smaller ones that are left eventually start growing?  They seem quite healthy and active. They're always scooting around the tank and sifting through the sand. 

[AllFishNoBrakes]

I’ve raised a few Cory species, but nothing in big numbers. I’ve also done livebearers, Bristlenose, and TONS of Angels. 
 

In my experience, regardless of species, you’ll always have the ones that dominate the food and grow faster. And then you have the runts. 
 

When I do Angels, I take the biggest 15 at a time to the LFS. Then I continue to grow out the rest. Another 15 to the store, continue to grow out. Then another 15 to the store. Rinse and repeat. 
 

I gotta say it’s pretty shocking that the first picture is of fish hatched in January. I also gotta say that the ones you sold are smaller than any Cory I’ve ever seen in a fish store. In 6 months I would expect them to be bigger, for sure. 
 

In general, does it take at least 6 months, in my experience, yes. Especially Cory’s in my experience. They’re much slower than say, my Angels that are pretty quick. 
 

I focus less on time and more on health. I just keep feeding them well, keep them in a stable environment, and when they’re ready I hit up the LFS and see if they’re ready for more, and typically they are. It’s a good cycle for both of us. 

[Rycraft]

@AllFishNoBrakes thank you for reaffirming.  That was very helpful.  Figured they might just be the runts/slow growers. The larger ones that I brought to the local fish store were definitely gobbling up all the food when they were still in there together. And to clarify the second pic of the larger one was still 4-5 weeks before I brought them in to the LFS.  

The ones left over are definitely very active and are eager eaters as soon as the food enters the tank so it looks like I just get to enjoy them in baby form for a bit longer. 

[jwcarlson]

I have only raised mine in trays in a fry "system" like Dean's.  With a 37 gallon aquarium as the base for the trays.  Had as many as 60+ corys in the trays with a tray of CPDs.  Was changing like 90% of water every day or every other.  Water can foul pretty darn easily.  What was their first food?  What are you feeding them now?

I've never had that big of size difference unless I felt there was some other problem (deformity, swim bladder issue, or something like that).  If they haven't grown much since getting rid of the bigger ones, they're probably not going to reach their potential.  Kind of strange situation.  I'd think they would take off if they were going to.

[Rycraft]

@jwcarlsonfirst food was frozen rotifers 3-4x a day. I also had them in there with some catappa leaves so there were some microorganisms to eat as the leaves broke down.  As they got bigger I started introducing frozen BBS and crushed up bug bites and flakes.  The 3 guys left seem to be growing some it's just VERY slowly. The largest of the three appears to be the size the original big boys hit at around day 60 or so.  

 

Also since it's just the three left I've started doing more targeted feedings and putting the food in the same spots which they have seemed to figure out.

[tike]

I have raised tons of cory fry. Mainly duplicareaus and eques. In my experience you will find you have some runts. I am a huge fan of feeding live bbs it makes their growth increase substantially. I also feed three times a day , the bottom will be covered in live bbs. After a few hours i will siphon all that is still left. The bellies of the babies will be noticeably pink. I do 80% water changes daily for the first 2 weeks. I hope that helps.  

[sumplkrum]

Sometimes you just get some bad ones. They should be young but fully formed by now - not still looking like a tadpole.
Could be genetic or developmental defects.