Blacksheep1 is correct; however, with growth hormones, it's not the actual "growth hormone" that stunts - instead, it's the GIH, or growth inhibiting hormone. Fish use this to suppress another fish's growth and can even suppress theirs if conditions are crowded enough.
Wonder why people talk about "stunted growth" in goldfish? They say it's water quality, bad food, overstocking, stress, and that stunted growth will kill fish...non of this is true. Carp (goldfish included) can live through an apocalypse. Not only that but they produce GIH in the wild too - even in giant lakes. One thing to note is that all of the oldest-living goldfish were stunted.
This may not sound relevant to the conversation, but it is. Although not much research is done for catfish relating to GIH and life expectancy, small animals often live longer than their counterparts. Think chihuahuas living 20 yrs while great danes only live around 6-8, or miniature horses living 40 yrs but the biggest horse breeds living only 20 at most. It's a similar situation with fish too.
For most fish, stunting is in fact good for the fish - a smaller size means more food and space is available, allowing fish to grow up healthier and often live longer. Unfortunately, I know all of this with many years of experience with goldfish, but I'm not so sure if this is the same with
corydoras
What I'm saying is, stunting can be good, but an overstocked tank full of sick, stressed fish isn't. So use all of this as you please. Do your frequent WCs if you choose, manually remove dead eggs, use
methylene blue or snails, or don't do any of it. It's all up to you on what you want to do. The most important thing with fry is having plentiful food and low
ammonia if you have high
pH (low pH produces ammonium only which is generally considered non-toxic.)
Nitrite isn't toxic for the most part, but it probably is for fry. High
nitrate isn't usually either, but may be for fry. Fry are a lot more sensitive than adult fish, so I suggest doing relatively frequent water changes; maybe every few days or so. Check
water parameters at least weekly and do water changes if anything looks off. I've done this for 12 years. If it works, it works!
As for food, this also depends on you. Many use
hikari first bites with great results but some say the ingredients are bad (which is somewhat true - despite the high price tag, hikari's not too good when it comes to
fish food ingredients.) Various worms like micro and vinegar eels are great but they're hard to find, can be expensive, and many times the colonies fail. Baby brine shrimp are a great source of protein and are fairly easy to find and hatch yourself. It may start to get expensive with hatching and feeding brine every 24 hrs but they'll grow up healthy. Another are
daphnia and moina - "water fleas" - basically the same thing. They're very easy to raise on plain algae and are healthier than most live foods (
bloodworms can cause bloating if fed too frequently, but daphnia and moina are a great way to treat this issue.)
So overall, one way to raise fry may not be the way you'd want to go, depending on your water. Catappa (indian almond) leaves are great and all but don't use them if you have low pH unless it's what you want.
Tannins,
CO2 from injection and high surface agitation, and high nitrogen caused by detritus can cause the pH to drop. Carbon will cause the pH to rise dangerously. I haven't used carbon in over 8 yrs. It's completely useless. My water from the tap has a pH of 6.8 - in a normal tank without high flow the pH buffers to 6.6, but in a tank with high flow the pH can be as low as 6.4 - too low for most fish besides anabantoids (labyrinth fish), and probably for cories too.
Anyway, sorry for the long reply, but I'm trying to cover everything in hopes that this'll help. Good luck
