Sterbai Corydora Sudden Death

Hi all,

After some thoughts on exactly what is going on with my newest additions to the tank.

Tank is a Juwel Rio 180, has been up and running nearly two years, with internal filter and a Fluval 306 external feeding in. Sand base as always wanted/kept corys. Tank has been stable and no livestock changes for over 6 months prior to this.

Stock list is as follows:
3 Neon Tetra
15 Lemon Tetra
12 Rummynose Tetra
1 Bristlenose Plec
3 Established Sterbai Corydoras

Yesterday we purchased 6 new Sterbai Corys from a well known shop they looked healthy as did all other fish in the store nothing to make me question buying their.

All six survived the ride home and after acclimatising in a standard fashion where introduced to the tank no drama and traveling water disposed of separately.

Come in from work today (28hrs+ after introduction) and have a look in tank and find all six sat normally on the tank floor. Two hours later when the lights come on find one dead on its side, net it out cursory look over of the body and no obvious injuries or obvious cause of death. - Put down as post travel stress and not overly concerned.

Two further hours and look at tank and find another laying on its side, after a minute it sits up and is breathing fast. Open tank lid to feed, and it goes bonkers very fast ascent to top quarter of the tank and then appears at the peek to die and plummet vertically to tank floor. Upon removal from tank an air bubble was observed in one set of gills but no other obvious signs of injury / cause of death.

The other four new corys have settled into the tank, and are behaving as you'd expect, no other fish is showing any signs of poor health or unusual behavior including the established corys.

No water change done since new arrivals - I'm concerned stress has already killed two and don't want to add additional stress if possible.

Any ideas whats going on? Or do we just have to chalk it up to experience and wait and see.

Sounds very much like shock. It can take days, even a week or two, to take its toll. Was the water they came in very different to your tank water, and if so did you take enough time to mix them?

Another possibility is that your original sterbai are coping happily with a disease presence that the new ones are not prepared for.

Btw (engage pedantic mode) they're called Corydoras, not Corydora.

If rhe water parameters are very different you need to acclimatise them very slowly, say over an hour or two at least. Especially if they're going from their preferred conditions to 'unnatural' ones.

Hi there and welcome to the forum 

Sorry to hear about your unfortunate recent experience.

I also live in an area with hard water, and this has caused me concerns in the past. I am in the lucky position of having a lot of local stores with helpful staff, including 2 branches of MA, and 2 independent ones with good reputations, all within a 20 minute drive. I've discussed this topic with all of them, and as a general rule they use treated tap water without RO, so their water should be roughly the same as yours.
Some will use a mix of tap & RO for particularly delicate species, some don't.
One of the independent stores has even given me information relating to the location and water conditions of their main supplier, which was interesting. Their supplier has slightly harder water than we do, which may complicate the picture further.
On top of that, all LFS have large filter systems which circulate the water through an entire section of tanks, rather than individual tanks like we do at home, so their fish will be in contact with numerous other fish species, which may have come from separate suppliers and different times.
They also use a medication regime, which again is something that wouldn't normally be done in the home aquarium, and which is probably very different from any medication regime used by the breeders/suppliers.
As the others have mentioned, some LFS don't quarantine fish for long, and stress is a major problem.
When you also consider that some fish are still caught in the wild, and put into the same systems, it is probably the equivalent of a human travelling the world several times over, without stopping for any length of time at any destination, on multiple modes of transport, mixing with people carrying various illnesses, and without any chance to relax and deal with their jet lag.
As I'm typing this I'm suddenly amazed that any of the fish survive.
Water parameters and the environments in which fish are kept are very complicated, and we can never really know what the fish we buy have been through before we get them home. This is little consolation when we see fish die, but sometimes these things happen.
It may also be worth using a quarantine tank for new fish, as there is also the possibility of new fish bringing disease to your existing fish, although that isn't the case here. I also feel (with no evidence whatsoever) that quarantine tanks are useful to help new fish get over the stress of travel without the added stress of dealing with new fish as well. You can also put extra hides & plants in the quarantine tank to provide more security for new fish, and medicate if any problems crop up, without having to medicate the main tank.
Again, sorry to hear that you have had problems, but there may have been nothing within your control that you could have done to avoid it.