Corydora Breeding Difficulties

[Ninebreaker]

Hey everyone, I have been having some difficulties breeding corydoras and would like some tips / advice.  

I have a decent sized group of Black Venezuelan Corydoras (~8) in a 20H as seen below.  I do cool water changes of >50% 1x a week and haven't been getting so much of a "corydora dance" out of them, let alone random eggs.  

As you can see, the setup has a sponge filter and a HOB filter (sorry, the coop pre-filter sponge is on there, but just fell off!).  I recently (~2 wks ago) also switched from gravel to sand since I know that helps.  About 1wk ago I added the java moss as well.  

Tankmates: 

Shrimp, a few snails, a few (3x) "lonely" tetras, and a few swordtails (probably like 5 or so). 

 

Diet: 

I feed the following foods 1x a day in general, "randomly" (no fixed schedule):

Repashy gel (they don't really like it, so I've been laying off) of soylent green / spawn n grow mix

Freeze Dried Tubifex 

Shrimp Pellets 

Red Wigglers (cut up)

Live baby brine shrimp (more for the swords / tetras, but weird, but they seem to react to the live food, even though they can't really get to the shrimp??)

Frozen mysis 

Frozen bloodworms

I probably feed mostly the frozen bloodworms probably 3-4 days a week and the shrimp pellets 1x a week, followed by one of the remaining foods. 

Water Parameters: 

My water is pretty hard, out of the tap it's something like 290-300TDS.  

The KH is pretty low (doesn't register on my liquid kit) and the pH is around 6.6.  Temp is around 70F. I keep the nitrates in the tank to about 20ppm with 1x a week water change of >50%. 

 

Any breeding advice would be helpful!

 

[FrozenFins]

I don't know much about corydora breeding, but I know that somefish won't breed when there are others in the tank. Also how many corys do you have? Maybe you dont have a female or male in the group

[Ninebreaker]

I have about 8 corys.  I'd find it hard to believe that there's not 1 female (or conversely 1 male). Not impossible, but improbable. 

I will say that there are a variety of sizes (from a few giant ones to smaller ones).  Since sexual dimorphism exists for corys to an extent, I believe there's at least a mix. 

Edited November 27, 2020 by Ninebreaker

[Andy's Fish Den]

How old are the fish? The cooler water changes should be a trigger, sometimes you may not see them do the dance and lay eggs because they do it after the lights are out. And with the other fish in the tank, they are probably eating the eggs before the lights come on. I would suggest moving them to their own tank, give them a week or two to settle in then do a nice cooler water change. You should then find eggs on the glass and or plants in the tank. 

[Ninebreaker]

10 hours ago, Andy's Fish Den said:

How old are the fish? The cooler water changes should be a trigger, sometimes you may not see them do the dance and lay eggs because they do it after the lights are out. And with the other fish in the tank, they are probably eating the eggs before the lights come on. I would suggest moving them to their own tank, give them a week or two to settle in then do a nice cooler water change. You should then find eggs on the glass and or plants in the tank. 

They're older. Someone before me bred the group, so I know they can breed.  They had been in their own tank for QT. But that was a few months back. 

I'll consider moving some of the swordtails out, but I do check at all hours of the night (like we're talking 2AM) and I really don't see any activity that's indicative that they would be laying eggs. 

Edited November 27, 2020 by Ninebreaker

[Coryndory]

Just throwing out some ideas since I’ve not kept these specific Corydoras.  How much food is actually making to the Corys?  Considering the tetras and swordtails, which can be aggressive feeders, make sure the Corys are getting good access to the food.  Sometimes it can take a good amount of food over a course of time to get them conditioned and ready.  I feel this is more important than the cool water changes.  With females of that age they should appear quite full/round when conditioned.

Yes, Corys will devour some baby brine.  Works great for raising the fry as well.  I’ve found mixed results with the repashy community blend.  Some of my groups really like it, others don’t show a ton of interest.  But it can be an easy way to put on weight as it stays stable in the water for a long time.  Don’t over feed with dried tubifex though as it can foul the water very easily.  Frozen bloodworms work great.  Also hikari vibra bites work good too.

70 degrees seems toward the cooler end to me.   Hopefully someone that has worked with these will be able to speak to that.  If the tank is 70, how cool is the water you are changing 65? cooler?  Are you changing 50% a week to control nitrates or just to induce spawning?  Have you tried maintaining a stable temp for weeks and not changing so much water at once?

For me, first thing in the morning is when I notice most spawning activity.  May be way before your tank lights come on if there is a window nearby or some other light source.  Some species of Corys themselves can be real aggressive at eating their eggs as well.  If they are, sometimes you will spot half eaten eggs or the outline of where an egg used to be on the glass.  They will also lay on rocks, wood, plants and in the sand so check there too.  
 

 

 

 

[Ninebreaker]

4 minutes ago, Coryndory said:

Just throwing out some ideas since I’ve not kept these specific Corydoras.  How much food is actually making to the Corys?  Considering the tetras and swordtails, which can be aggressive feeders, make sure the Corys are getting good access to the food.  Sometimes it can take a good amount of food over a course of time to get them conditioned and ready.  I feel this is more important than the cool water changes.  With females of that age they should appear quite full/round when conditioned.

Yes, Corys will devour some baby brine.  Works great for raising the fry as well.  I’ve found mixed results with the repashy community blend.  Some of my groups really like it, others don’t show a ton of interest.  But it can be an easy way to put on weight as it stays stable in the water for a long time.  Don’t over feed with dried tubifex though as it can foul the water very easily.  Frozen bloodworms work great.  Also hikari vibra bites work good too.

70 degrees seems toward the cooler end to me.   Hopefully someone that has worked with these will be able to speak to that.  If the tank is 70, how cool is the water you are changing 65? cooler?  Are you changing 50% a week to control nitrates or just to induce spawning?  Have you tried maintaining a stable temp for weeks and not changing so much water at once?

For me, first thing in the morning is when I notice most spawning activity.  May be way before your tank lights come on if there is a window nearby or some other light source.  Some species of Corys themselves can be real aggressive at eating their eggs as well.  If they are, sometimes you will spot half eaten eggs or the outline of where an egg used to be on the glass.  They will also lay on rocks, wood, plants and in the sand so check there too.  
 

 

 

 

Thanks for the suggestions.  

Usually, I feed quite a bit of food, so I know it's making to the Corydoras.  Yes, the swordtails do pick stuff from the bottom, but the problem is the nitrates getting too high if I feed way too much, which is part of the reason I change water at so high a %, but I also heard it was good for spawning. It kind of is serving double duty. I'll be honest and say the swordtails that are in there look like little balloons they're so fat.  Probably overfeeding the swordtails, but it's only to get to the corydoras. 

The guy before who bred them keeps at room temp.  Generally "room temp" in New England means around 68-70F for us by his reckoning.   I have a feeling breeding was too inconsistent for him, which is why he gave up on it. 

As far as how cold the water is when I change, it's pretty cold.  I'm not sure of the temp exactly, but a quick temp check of my water shows it's 60F.  

I've not tried the lower % water change, but maybe multiple times a week with lower % water changes would help. Now that you do mention it, my other corys seemed to do better (as in, they bred also in a tank with swords) when I "did nothing" (I got super busy and didn't change water for a month or so...). Maybe I should try more frequent, smaller percent water changes and see how that goes. 

I would say that the swords likely aren't eating the eggs only because I have another tank with corys in there and they seem to leave the eggs (when they do appear) alone. I've not seen any eggs at all, which is weird (to me).  I do have an idea of what the "sticky spot" looks like when an egg gets eaten. 

 

[Coryndory]

I would maybe try smaller more frequent water changes with less temp fluctuation for a period and see how that goes and then hit them with the cooler 50% if need be.  Sometimes we try too hard and change things too much.  I know I'm guilty of this.

Other options:

Mixing your water with RO to cut the TDS when doing a water change.  Could be worth a try, but watch ph as you already have no buffering.  Can also tag team this with a large pressure swing due to incoming storm.
 

Since you have another tank with Corys, you could try pulling water from that tank when they are spawning and changing it into this tank.  This is a trick used by some breeders as it is believed chemical compounds are released in the water that can trigger spawning in other groups.

I wish you luck!

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[Ninebreaker]

Thanks! I will try not fluctuating the temp for awhile and smaller WCs.  Then do a larger change. I'll try 3 weeks of it. Seems like a good start. 

I'll stick to 2x a week maybe 10 to 25%.  Less volume should mean less fluctuating temps regardless. 

I don't have RODI, but I'll try this for a bit before buying a unit. 

I haven't seen their buddies spawn in a few months, but if they start doing it, I'll hit them with the WC water. 

[ChefConfit]

Corys like stable water parameters and large water changes mean large swings in water chemistry. I'd try to extend the time between changes and/or lower the % you change. Mine started breeding for me after I added crushed corral which raised my kh and switched to biweekly water changes. If you have a problem with nitrates getting too high you can try adding some really fast growing plants to soak it up. Right now other than your floaters your plants look to be all slow growing. 

Fish also are more likely to make babies when there is food around for said babies. Try feeding smaller amounts more often so that there is food around all the time not just for a little bit each day. The fry will need to eat a few times a day anyway so you might as well get used to it now. 

Also with 8 corys there's a 22.333% chance that they are all the same gender. It's unlikely but it's better than a 1in5 chance that they're all the same gender. But your comment about them having varying body sizes would suggest you have a mix. 

[Ninebreaker]

1 minute ago, ChefConfit said:

Corys like stable water parameters and large water changes mean large swings in water chemistry. I'd try to extend the time between changes and/or lower the % you change. Mine started breeding for me after I added crushed corral which raised my kh and switched to biweekly water changes. If you have a problem with nitrates getting too high you can try adding some really fast growing plants to soak it up. Right now other than your floaters your plants look to be all slow growing. 

Fish also are more likely to make babies when there is food around for said babies. Try feeding smaller amounts more often so that there is food around all the time not just for a little bit each day. The fry will need to eat a few times a day anyway so you might as well get used to it now. 

Also with 8 corys there's a 22.333% chance that they are all the same gender. It's unlikely but it's better than a 1in5 chance that they're all the same gender. But your comment about them having varying body sizes would suggest you have a mix. 

I have a bag of aragonite. Would that work? 

I have put it in my filter, but it seems like the hardness gets "sucked out" quickly.  I did (for kicks) put a few pieces of aragonite into tank water to try my kit and it seems to work.  So Idk why it's not going into the water with the flow.

[ChefConfit]

By sucked out quickly do you mean you see a rise in kh but then it drops back down again? If that's the case I'd be inclined to say your large water changes are to blame and we're back to finding a way to slow the buildup of nitrates so you can change less water and keep the parameters stable. 

[Ninebreaker]

Just now, ChefConfit said:

By sucked out quickly do you mean you see a rise in kh but then it drops back down again? If that's the case I'd be inclined to say your large water changes are to blame and we're back to finding a way to slow the buildup of nitrates so you can change less water and keep the parameters stable. 

Well... I see a rise in kH locally (water locally right out of the filter seems to change kH slightly), but for some reason the rest of the tank doesn't seem to get the effect.  My thought is that the plants may be sucking some minerals because there's so few minerals in the water.

I suspect something is off because there's almost no snails in that tank... 

I do have hornwart in the tank, so I thought that should be fast growing.  Seems like not much grows quickly.  I do use root tabs and ferts, but never have been able to get a ton to grow in that tank. 

You're probably right that the large water changes that keeps the kH knocked down. I could probably try some wonder shells or crushed coral to help buffer if argonite isn't helping/working.

Just on a side note, I cannot for the life of me grow green water in any tank I have, so that might be useful info. 

[FrostiesFishes]

In my experience Cory’s species are typically harder to spawn then most others. And I’ve had limited experience with the species I’ve bred breeding on a regular schedule. And a lot of them require soft/ low ph to trigger spawning. I’ve got a group of orange laser cw10 that I know I have both sexes. I’ve had for over two years in a species only tank. And I’ve never had spawning activity. But I don’t use Ro water, I’m just to busy with other stuff. But a lot of people will also say water level, seasonal lighting and other factors can effect spawning behavior. 

[Fish Folk]

We had a terrible time trying to spawn a group of Corydoras Aeneus (Bronze Corys) until very recently. If you've ever seen any eggs at all, then they are likely being eaten by the swordtails or the tetras. A powerhead may help, as they do like flow in the tank. Getting good food through them is probably more important than cold water changes. Your feeding variety looks great! Perhaps try changing water when barometric pressure drops in your area. Also . . . this is a little crazy . . . timing water changes to a week when there's a full moon sometimes helps. Ours spawned right after we added a bunch of crypt parva. We also added oak leaf litter, some alder cones, and a few catapa leaves. When they're comfortable, they do spawn!

Edited November 29, 2020 by Fish Folk

[Coryndory]

Between the large water changes and plants the effects of the aragonite are prob minimal.  

If trying to reduce nitrates to extend water changes, what ferts are you dosing?  Does it have nitrates in it?  With the bio load in the tank, wouldn’t think you would need the additional nitrogen. Hornwort should consume a good amount of nitrates, as would any other floating plant if there is a good amount of it.  Ultimately, the easiest way to reduce nitrates would be to reduce bioload.

I agree that stable conditions are important.  For reference, my water is soft, avgs 6.2-6.4 ph, and has pretty much zero kh.  I change water to maintain nitrates and try to keep the water I am changing pretty close in temp to what is in the tank.  In a ten gallon with 10+ Corys this for me is 40-50% a week, in my 20s I only change 20-30% every week or even every other week in my 29.  Despite the difference in amount of water changes I am spawning Corys in all of these tanks with 2 spawns a week in the same tank being not uncommon, albeit they aren’t species which are known to be difficult to spawn like a weiztmani or eques.  I live in GA and in the summer my water comes out of the tap warmer than some of my tanks by 5+ degrees and I don’t cool it yet the Corys will still spawn, this is why I don’t think the cool water change is a necessity.

FWIW I tried running hard water in one of my tanks for a while by dosing Equilibrium and it did slow the Corys spawning in there.  You can also get RO at most grocery stores at those jug filling machines if you wanted to go down that route at some point.
 

 

[hamlet10]

On 11/27/2020 at 10:02 PM, ChefConfit said:

Also with 8 corys there's a 22.333% chance that they are all the same gender. It's unlikely but it's better than a 1in5 chance that they're all the same gender. But your comment about them having varying body sizes would suggest you have a mix. 

How did you come up with that number?  

By my math, assuming that each fish has a 50% of being either gender, the odds of them all being one gender is less than one percent.  Two would be 50% chance, three would be 25%, four would be 12.5%, etc.

Now that is assuming that they are all random genders, and sometimes weird things can happen in the environment or the fish selection process that give unbalanced ratios.

[ChefConfit]

@hamlet10 with 8 fish there are 9 possible gender distributions ranging from 0 males to 8 males. Of those 9 possible distributions 7 contain at least 1 of each gender. 7(number of favorable distributions)/9(number of possible distribution) multiplied by 100 gives us a 77.777repeating% chance of a favorable distribution which gives us a 22.222repeating% chance of an unfavorable distribution. I subtracted repeating decimals wrong at the very end in my original answer and it was 0.111repeating off. 

[hamlet10]

7 hours ago, ChefConfit said:

@hamlet10 with 8 fish there are 9 possible gender distributions ranging from 0 males to 8 males. Of those 9 possible distributions 7 contain at least 1 of each gender. 7(number of favorable distributions)/9(number of possible distribution) multiplied by 100 gives us a 77.777repeating% chance of a favorable distribution which gives us a 22.222repeating% chance of an unfavorable distribution. I subtracted repeating decimals wrong at the very end in my original answer and it was 0.111repeating off. 

That doesn’t work because the gender distributions aren’t equally likely.  It’s like rolling two dice - you can get 2 through 12, but rolling a 2 or 12 is only a 1/36 chance, while rolling a 7 is a 1/6 chance.  There are more combinations that make 7, while only one that makes either 2 or 12.
 

The chance of eight fish all randomly being the same gender is the same as flipping a coin and having it come up heads or tails 8 times in a row.  1/128, or less than 1%.

 

[ChefConfit]

@hamlet10yea it's been a long time since I took statistics. Your math seems better. I remember a coop video giving a number in the teens to give a 90% chance of getting a pair which lined up with my math so I assumed mine was right. 

[Tonik]

My Panda Corys show spawning behavior all the time, but I have only had one fry grow up, probably because they are in a community tank with sword tails and tetras.  One thing I do, which may help, is to use a pipette to put the bloodworms into the sand so they can burrow around and get them.  That way they are not mostly eaten by everyone else.  I also have a heavily planted tank and they seem to like dropping eggs in a patch of java/Christmas moss which is about 2 1/2 inches tall.  This means I can't get to the eggs but in a species specific tank, it might help?

Good luck!

[Joshua14]

Personally I would remove any other fish. Let them run the tank. Don't stress so much on the cool water changes, and find yourself a alder cone or catappa leafs to toss in there. Feed them like you think it might kill them. 🤪

Edited November 30, 2020 by Joshua14

[Ninebreaker]

On 11/28/2020 at 11:52 PM, Coryndory said:

Between the large water changes and plants the effects of the aragonite are prob minimal.  

If trying to reduce nitrates to extend water changes, what ferts are you dosing?  Does it have nitrates in it?  With the bio load in the tank, wouldn’t think you would need the additional nitrogen. Hornwort should consume a good amount of nitrates, as would any other floating plant if there is a good amount of it.  Ultimately, the easiest way to reduce nitrates would be to reduce bioload.

I agree that stable conditions are important.  For reference, my water is soft, avgs 6.2-6.4 ph, and has pretty much zero kh.  I change water to maintain nitrates and try to keep the water I am changing pretty close in temp to what is in the tank.  In a ten gallon with 10+ Corys this for me is 40-50% a week, in my 20s I only change 20-30% every week or even every other week in my 29.  Despite the difference in amount of water changes I am spawning Corys in all of these tanks with 2 spawns a week in the same tank being not uncommon, albeit they aren’t species which are known to be difficult to spawn like a weiztmani or eques.  I live in GA and in the summer my water comes out of the tap warmer than some of my tanks by 5+ degrees and I don’t cool it yet the Corys will still spawn, this is why I don’t think the cool water change is a necessity.

FWIW I tried running hard water in one of my tanks for a while by dosing Equilibrium and it did slow the Corys spawning in there.  You can also get RO at most grocery stores at those jug filling machines if you wanted to go down that route at some point.
 

 

Yeah, I honestly have super soft water, but I'm dosing my own ferts.  The ferts do not have any nitrates in it. Long story short, I used to use NilocG ThriveC, but found out that my tanks have nitrates, but literally nothing else in it, hah.  It's super soft. Basically, I can't get much to grow unless I use root tabs and ferts.  I should probably do less water changing as my fish are probably knocked around a bit. 

Initially I thought I had hard water because the TDS was like 300, but got a KH / GH test kit and wondered wtf was going on with a high TDS, but 0KH.  

I mean, technically black Venezuelan corydoras are just Schulztei with a different coloration.  The guy I bought them from spawned them locally before he moved.  

 

[Ninebreaker]

15 hours ago, Joshua14 said:

Personally I would remove any other fish. Let them run the tank. Don't stress so much on the cool water changes, and find yourself a alder cone or catappa leafs to toss in there. Feed them like you think it might kill them. 🤪

Oh yeah, I put in the leaves already.  I feed the fish so much that I might kill the swordtails first, hah.  

Seriously, there's so much food just sitting there, the swordtails ignore it.  Swordtails ignoring food is like my dog ignoring food.  Something has to be wrong with it or they're bloated, lol. 

I EVEN found blackworms GROWING in the tank itself (which I discovered after removing the substrate) and they were like.. MEH... I mean... Corys are supposed to root around and find that stuff.... 

I used to have the corys in a tank by themselves and they were so frightened of everything, which is why I moved them in the first place and figured they could use the "dithers" up above.  They seemed to come out after that.  I have some rice fish I could put in there, but I just got them in, so they need QT time.  

I might end up pulling the swordtails though after a few weeks of no water changes.  I don't want to stress everyone out at the moment.  I'm sure you know stress + corydoras = death and since I would be doing small water changes, stress + small water change = potential harm from toxins. 

[Ninebreaker]

On 11/28/2020 at 11:12 PM, FrostiesFishes said:

In my experience Cory’s species are typically harder to spawn then most others. And I’ve had limited experience with the species I’ve bred breeding on a regular schedule. And a lot of them require soft/ low ph to trigger spawning. I’ve got a group of orange laser cw10 that I know I have both sexes. I’ve had for over two years in a species only tank. And I’ve never had spawning activity. But I don’t use Ro water, I’m just to busy with other stuff. But a lot of people will also say water level, seasonal lighting and other factors can effect spawning behavior. 

Yeah, I have CW010s too... mine spawned in my swordtail tank several times once I got them (about 1.5 yr ago) and then just never really did again.  I think in October, I start getting busy with work and "ignoring" the tanks, which may have had something to do with it.  

I had mine spawn again in about September / October last year too.  It's super seasonal and I presume it has something to do with temp + light because my old house had a huge temp swing and the tank was next to a window.  My new one has less of a swing and almost no natural light.  Same plants and everything.