C. Panda. Have Stopped Spawning

[Biffa]

Hi everyone, I've searched and searched the internet for a sensible answer to my question, but can't seem to find one. Found this site amongst my interwebby travels, so thought I'd register and ask for help/advice and whatnot. Apologies if this is a daft question.

So, a very simple question, does anyone have any sort of idea why my C. Pandas have stopped spawning?
It's been more than a year.
I currently have a school of 26 (I think).

Thanks if anyone can help. I'm very busy with work at the moment (heading out now actually) but will obviously pop back in, in a day or so to see if anyone has any ideas.

A quick back history.
Being a complete and total novice and numbskull, four or so years ago, I bought my first and current aquarium. Having absolutely no idea whatsoever about Cycling a tank (I know!) I went out and bought 9 C. Panda along with the food they told me to buy. I took them home and duly added to the tank.
Then, that afternoon I decided to research the species and to find out what I needed to do. Ignorant I know, but I genuinely thought you put fish in water and fed them and changed the water once a week. What a learning curve I hit!
So, what followed was more water changes and more money spent on aquasafe than I care (or want) to remember. Carrying buckets of water before work, after work, before bed and on a few occasions in the middle of the night! I thought the wife was gonna file for divorce at one point! My entire life seemed to revolve around API testing and carrying water. Luckily, thankfully, more by luck than judgement, I cycled the tank without a single loss. I actually felt a great sense of achievement but even now I hope none of the wee lads and lasses suffered due to my ignorance.
Scared of triggering another mini cycle, I left the gang as they were. Long story short, those 9 are now 26. I've never once 'assisted' by removing eggs. Only fish I've ever bought since the original 9 are the Otto's. (Tank is Panda and Otto only) After every Panda spawning, I let nature take its course.
Eggs used to pop up everywhere. Of course many would get eaten, but obviously some survived.
Approximately 18 months ago, the spawning dwindled and just over a year ago they eventually ceased completely.
Nothing has changed within the tank with regards to temperature, or any water chemistry. I haven't rearranged bogwood/plants etc. The substrate is the same since day 1. Water flow, aeration, all the same as it's always been. I must have been very lucky when I chose the sand originally as there's no discernable barbell damage I can see. My maintenance routines are the same as they've always been. I'm stumped as to why the spawning has stopped. Feeding is exactly the same as always, as varied as possible. I just don't understand.
Is it something obvious? Is it normal?
Everything else seems completely fine.
Thanks for reading and I hope it's not a stupid question. I'm not concerned on my behalf that the gang have become celebate, I'm concerned about the gang in case I'm doing something wrong. I'm very much the novice! I think I always will be with the cheeky bunch.

All the best

Bif.

ps. I've filled in the health question thingy, but it's not really (I hope not) a health problem.

1. Water parameters
a) Temperature range 22.5
b) pH 6.8
c) GH 8
d) KH 7.2
e) Ammonia 0, Nitrite 0, Nitrate never higher than 15.
f) Water change frequency 25%, 3 times a week.

2. Tank set up
a) Size 300L
b) Substrate, Sand (can't remember the brand, approx 1 inch deep)
c) Filtration, x2 Fluval U3 internals, one each end of tank.
d) Furnishings, lots of Bogwood, lots of Anubias and Moss. Few small rocks, big pebbles etc amongst bogwood to provide hideyholes.
e) Other tank mates.
x6 Ottocinclus
f) How long has it been set-up?
4+ Years
3. Symptoms / Problem description
Lack of Spawning
4. Action taken (if any)
N/A
5. Medications used (if any)
N/A

[Corycory]

It was a good read. Well done with the pandas.
It's hard to tell what caused them to stop breeding. It sounds as if you are taking very good care of them and there is no obvious reason.
Some corys tend to be seasonal spawning wise. Mine tend to go nuts around this time of the year each year even if they slowed down over the winter.

If the fish are healthy otherwise and not acting shy and more spooked than usual, I wouldn't do any drastic changes at all.
What I would try, is a complete water refresh. Which means, do back to back water changes daily for a week or two to exchange all water gradually. Older tanks tend to change their chemistry despite what the tests show you and that's because there are no tests available to show you the full picture.
And although you are doing enough with 3x25% a week to keep healthy fish, each water change doesn't exchange much of the water at a time, meaning the tank chemistry has slowly but surely altered over the years.
It will take a couple of months at that rate to exchange all water and by then the chemistry still works against you, so imagine what 4 years can do.
So I'd gradually increase the amount of water changes each time to reach a 50% water change at a time, and do that daily or every 2nd day for two weeks at least which will totally get the tank water back to your tap water chemistry.

If that works for spawning, I'd incorporate a large water change each week alongside the 25% ones long term, especially if you are doing it via a python system as its as easy changing 25% as is 50%.

Someone else might have better ideas but mine won't hurt the fish. Corys love large water changes.

[bekateen]

Hi Biffa,

I hope someone else can comment on this, but are pandas known to eat their own eggs? I know some other Corys do.

My thought is that even though your tank is big enough, is it possible that by going from 9 pandas to 26, you've just got such a big group that they eat all the eggs now?

Alternatively, could it be that they don't like the social setting? I know some people take Cory groups and break them up to get certain male:female ratios and numbers. The right choice may vary from species to species.

Good luck, Eric

[rmc]

Hi Biffa,
I agree with Eric here in that you may have a large enough group now that eggs are getting eaten. I've had tanks of Corys where they breed once a week for a very long time, but if I leave fry in the tank while the adults don't eat the eggs the fry do. The adults may not consider the eggs a food source, but fish more fish in the tank there is less food to go around, the fry who are typically even a little hungrier than the adults may have started eating eggs after one of the spawns, and now they look at eggs as a food source, and are for lack of better words - "good at finding and eating eggs."

That being said I've seen groups of Corys including C.weitzmani which is morphologically similar to C.panda be voracious egg eaters, and fish that won't touch the eggs even spawn to spawn. One spawn I'll actually witness the Corys gobbling down eggs as they are laid, the next spawn I'll find 50 eggs untouched hours after they were laid. A good rule of thumb for any fish including Corys is "if it fits in the mouth it may be eaten" and unfortunately in most cases Cory eggs do fit in Cory mouths.

If you want to start spawning them again you can try introducing floating or sunken spawning mops, so that when the eggs are laid they are better hidden, or better yet get a smaller aquarium (even a 30L tank would be just fine) and move 2 of the larger females and 4 males into that tank with some java moss, a spawning mop, etc. They will have less competition for food, it will be easier for them to find and eat the food you put in, and it should get into the spawning mood much more easily, with good 50% weekly water changes of course. If you do it this way and want to remove the eggs and hatch them out, you should be able to produce many, many more fry. I've been breeding my panda group since last December and I'm sure I easily have 60 fry. If I collected the eggs every time they laid I'd have hundreds.

Cheers,

Rob

[PabloG]

Hi Biffa,
I agree with Corycory on water changes and I agree with rmc on spawning mops
I have about 20 panda in the same tank.
I have only one spawning mop, but its tail goes up to the middle on the water column, so the pandas must go hi only to spawn and are on the bottom the other time. I have some anubias where they go to lay eggs too (tail anubias).
I make 25% twice weekly, and a 50% to 70% once a month to try a complete water refresh as Corycory said.
At the moment of 50% change, the water in the tanks is at ph6.5. I use rainy water collected in a swimming pool with lots of floating plants, with a Ph lower than 6.5, so I correct with sodium bicarbonate on a dose of 1/4 teaspoon for 5 galon aprox to get ph7.5 on the new water. The new water is 5 to 10 celsius degrees lower, so the resulting exchange lowers 3 to 4 celsius degrees the total aquarium water with PH7.0. On the 25% changes I don't modify the PH, so it goes down to 6.5 in the aquarium with all the 25% changes again.
It is not done intentionally to spawn, but if the big change occurs 1 or 2 days previously to a rainy day, they spawn.