Breeding of Corydoras

[Theblobfishman]

When i came home from college i was surprised to see one of my bronze corydoras depositing eggs onto a sword plant. it came as a surprise because i had over the course of about 2 months to get them to spawn with water changes and what not. I am writing this to put out what caused them to spawn, yesterday i had recently gotten my package for KNO3 and dosed it, causing me believe that perhaps that the reason they had not spawned was due to a lack of nitrogen in the water.

Just my thoughts

[Karsten S.]

Hi,

I'm doubting pretty much that the reason for spawning was lack of nitrogen/nitrate in the water. Otherwise most corys would have died out in nature .
In most of the natural habitats you will not be able to measure relevant quantities of nitrogeneous compounds, usually it will be much less than we have in the tab water and our tanks.

I would rather assume that it was not due to that particular salt but the increase of the conductivity or osmotic pressure of the water.
Basically many Corydoras species start to spawn when they "detect" the start of the rainy season. Different species have developped diffent methods (changed temperature, increased water flow, changed water parameters, availability of special food, changed turbidity,...).
With Corydoras aeneus usually a big water change with cool water is enough if the females are gravid.

Cheers,

[Theblobfishman]

And while I belive most of what you are saying is accurate I hadn't done a water change in over 2 weeks, with a consistant feeding schedule that didn't change. The only thing that change was the amount of nitrogen in the water. Perhaps a coincidence but my brain figures that where corydoras aneus is naturally found you would find decomposing wood and plants in the water so their would be some nitrogen compounds in the water. My plants use all macros in the tank. All I'm saying it could be a coincidence but perhaps a small ppm of plant soulable nitrogen could influence their spawning.

[Theblobfishman]

Also don't really like doing large water changes I have done 1 in 4 years. Also should rule out other things like even the ratio of males to females. I have 1 male and 5 females, male is the youngest I've had him for 3 months ish, I worked at the pet supply store where I got him so I know he was healthy, he is over 4 months at the least. 3 of them were bought at a P fish store but 1 was bought 3 years before the other 2. 3 were bought in the course of 9 months at the store I worked at. Water is tea colored due to driftwood, densely planted, 20 tall, all healthy. Recently got a pair of juv skunk cories and an agassizi Cory that was with em.

[Lycosid]

Perhaps a coincidence but my brain figures that where corydoras aneus is naturally found you would find decomposing wood and plants in the water so their would be some nitrogen compounds in the water.

1) There's no need to guess, this is a water parameter people measure.
2) Decomposing plants have relatively little nitrogen in them compared to the scraps of animal protein that get lost in your tank when the fish don't eat all their food.

The only thing that change was the amount of nitrogen in the water.

And the level of potassium ions. KNO3 ionizes to K+ and NO3- in water. Potassium is biologically-active and needed in many body functions, so it is possible that your fish reacted to this, either because they had a potassium deficiency or because the addition of potassium caused something like a change in osmotic pressure that mimicked a rain.

Given what we do know about nitrogen I wouldn't rule out the potassium.

[Theblobfishman]

Some helpful info would be that I already have been dosing K2SO4 which has higher levels of potash than KNO3.

[Theblobfishman]

Also plants need soluable K it can't take direct K+ it needs potash K2O

[pleco_breeder]

As has already been stated, the more likely cause is a change in the environment. Nitrogen in any form is actually toxic at the levels we're able to test with aquarium kits. The guidelines generally given are based upon "acceptable" levels and are several orders of magnitude higher than anything that will be found in all but the most critical environments in nature.

Corydoras are riverine, so are not likely to be found in an enclosed environment where nutrients would accumulate to extreme conditions outside the dry season.

Having said all of that, I have seen instances in planted tanks which involved a change in nutrient uptake because of the addition of a limiting nutrient. In those instances, a sudden uptake of nutrients, because of growth, actually lowered the conductivity of the system relatively quickly. This has only been noted when a couple of conditions were met. The first is that it be a plant capable of rapid growth when optimum conditions are met. The second is that those conditions are met, or become adequate to spur rapid growth. The third is that there be a sufficient amount of living plants already surviving to create this change.

The good news is that your plants are likely doing a more efficient job of removing excess metabolites with the new fertilizer addition. The bad news is that the tank has likely been sitting on the razors edge of a crash for some time in order for it to have been able to make such a drastic difference.

Larry Vires

[Theblobfishman]

1) not all forms of nitrogen are toxic to corydoras, every time they go up for air they take in nitrogen.

2) the areas where they have collected wild corydoras aneus are stream like in fashion, if you never seen the difference streams are typically slower moving, their are areas where nutrients do collect

[dw1305]

Hi all,
I agree with the others,the only thing I would say is that, when nitrate isn't the g gun of earlier higher levels of ammonia and nitrite, it isn't particularly toxic. Aquascapers often use KNO3 as a plant fertiliser and add ~30ppm NO3 without any effects on fish health.

Also plants need soluble K it can't take direct K+ it needs potash K2O

It is the other way around, plants (including terrestrial ones) can only take up nutrients as ions (K+).

In the case of the alkali metals all their compounds are soluble, so whatever potassium compound you add it will go into solution as K+ ions. All K+ ions are the same, they don't "know" which compound they came from.

1) not all forms of nitrogen are toxic to corydoras, every time they go up for air they take in nitrogen.

That is different, the molecule N2 gas is pretty much inert, this is because there is a triple bond between the two nitrogen atoms, and it takes a lot of energy to split that bond (which is why explosive like TNT are nitrogen based). Nitrogen atoms on their own are highly reactive and form a range of biocompounds, we call this "fixed nitrogen (https://en.wikipedia.org/wiki/Nitrogen_fixation)" to differentiate it from the N2 molecule.

cheers Darrel

[Karsten S.]

Hi,

2) the areas where they have collected wild corydoras aneus are stream like in fashion, if you never seen the difference streams are typically slower moving, their are areas where nutrients do collect

I have collected many different species of Corydoras. So I know quite a few habitats where you can find Corydoras in different countries of South America and have also seen several habitats of Corydoras aeneus. Up to now we never found them in the main rivers but always in small tributaries inside the jungle.
In the dry season they might be captured also in small ponds without water flow but all the trees would absorb all nutrients from the water before they can accumulate and most Corydoras definitly do not spawn during dry season and none in these ponds.

The trigger of your spawning succes is definitely not directly or explicitly NO3 and corys don't need it or can ever lack of it in our tanks. You never can find this high levels in nature unless perhaps if at the end of the dry season all fish in such a small pond die within a short time frame due to over heating.

However, KNO3 might have an indirect effect as already proposed by others.

Cheers,

[Theblobfishman]

Thanks to everyone for the info and I will continue to investigate.

[Lycosid]

Just to give you an example of some really strange changes in aquaria without any obvious cause, I maintained an ecosystem tank for almost five years without ever feeding or treating it. It was a 55 gallon tank with an overhead light and a bubbler. No filtration, no feeding, no water changes. Sometimes I had to add water to offset evaporation and sometimes I added organisms or other things I wanted to establish in the tank, but most of the time the tank sat untouched. During one of these long periods in which nothing was done to the tank it suddenly became full of tiny, pink spheres in the first few inches of surface water. Closer examination revealed these to be colonies of rotifers. For a period of about two weeks these rotifers, which I had never seen before, were found in extremely large numbers. Then they all disappeared and for the next two years I never saw them again. (Then I radically altered the tank.)

My best guess is that the sunlight coming in the window changed as the seasons changed and that this interacted with the position of the plants in such a way as to cause a phytoplankton bloom that caused previously dormant rotifers to reach outbreak proportions. However, given the actual data I have, I might as well claim that it was unicorn magic. Had I done something in the tank randomly a week before, like move some rocks to clean the bubbler bar, I probably would have (falsely) attributed the change to that action.