Zebra Danios Mating Behaviour?

[patfish]

We have a mature (18 month) 3 gallon tank that has happily supported 3 danios and one (possibly the world's fattest) tiger barb for the past year.
Recently, the three danios (one is much larger than the other two) appeared to be spawning, in that they were flailiing their little bodies against each other as they dodged through the network of hiding places at the bottom of the tank.
More recently, the two smaller ones have taken to lying on the tank bottom, as if they were dying. One does this more often than the other. Both appear to swim normally when the do get up to swim.

Now that the snail has found their corner, they are not leaving at all. They both lay there, still breathing, being crawled on by the snail.
Are they protecting eggs? Are they dying? Both?
I should note that the beginning of the change in danio behaviour coiincided with the introduction of the solo snail.
There are now at least two snail babies we have seen.

 

[TPIRman]

Danios are egg scatterers and, if left to themselves, tend to eat their eggs almost immediately after spawning.

What you are experiencing sounds like ammonia poisoning. They are indeed dying, likely because the snail you added to that small tank created an ammonia spike. Three danios and a tiger barb were already pushing it in a 3-gallon -- my guess is that the addition of the snail exceeds the biological capacity of that tank.

What you can do is perform a 50% water change as soon as possible to reduce the toxins, and continue doing so daily. That's the short-term solution. The long-term solution is a bigger tank -- a 10-gallon is probably the minimum suitable size for danios and tiger barbs.

The danios may not survive despite your best efforts. Any fish that is so unresponsive as to let a snail crawl over it -- especially a zippy danio -- is probably pretty far gone.

Consider buying a larger tank for your fish -- you will find that the danios will be much more fun if given some room to swim.

Sorry to hear about your troubles, and I hope this helps.

-John

 

[kikuchiyo]

Yeah, those 3 gallon tanks aren't good for more than one small fish and all the fish you have in there like to be in groups.

Any fish that submits to being crawled on by a snail has, effectively, kicked the bucket.

 

[patfish]

You're probably right... but

You are probably right about tank size.

We had the inch per gallon going okay until Barb ballooned into a halibut.

We've done several water changes since this behaviour began. Everytime we see one or both of the smaller danios lying on their sides, we begin the discussion of whether we should clear them out of there.
By the time we find the net, they are both back up, swimming around looking fine, and are generally more interested in continuing the mating frenzy, although they'll gulp a few bites of food down first.

Does that still sound like ammonia poisoning is the only thing going on?

 

[TPIRman]

Re: You're probably right... but

Originally posted by patfish
You are probably right about tank size.

We had the inch per gallon going okay until Barb ballooned into a halibut.

Does that still sound like ammonia poisoning is the only thing going on?

That's the way it sounds, yes. What you're seeing is definitely stress rather than mating behavior. When danios spawn, the male will chase the female around the tank and embrace her a few times, causing her to drop eggs. This might go on for an hour or two at most. And then they're done. It takes some time for a female danio to regenerate her stock of eggs, so they won't spawn again for a while.

Probably the reason that the water changes are ineffective is that you are fighting a losing battle in this small a tank -- the bioload is just too great for three gallons of water. This is why you saw the change in behavior when you added the snail. The additional waste generated by that creature was the straw that broke the camel's back, unfortunately, for the tank.

Here's a good thread on the inch-per-gallon rule/myth:

http://www.aquariacentral.com/forums/showthread.php?s=&threadid=26409

Picking up a 10-gallon tank still seems like the best solution to me. It's not very expensive at all, and it will pay dividends in terms of fish health and your enjoyment.

 

[patfish]

Thanks everyone,

The short term solution we've adopted is more frequent water changes and the transfer of one (or more) snail(s) as soon as we can catch them to our other three gallon tank which currently hosts 4 tiny 1/2 inch neons and one white cloud. And of course, step up the water changes in the second tank when we increase its bio-load with the snail.

Long-term solution will get started today. I'll buy a 15 to 20 gallon tank and start priming it for everybody's eventual transfer. We'll keep the set of threes for breeding, isolation and other special needs.
Thanks again for the input.

By the way, our danios exhibited the mating behaviour you describe for about 72 hours straight before they started the males started laying about on the gravel exhausted.

Everybody's been up swimming again since the last water change, but one male still seems a bit punked, hiding out in his cave a lot.