Corydoras sterbai dying

[Katov]

Hi!
New to freshwater, but not new to aquariums.
My son wanted an aquarium with catfish. We did some research, and it seemed like Corydoras would possibly work. Corydoras Sterbai looked the most like the larger catfish to him, so that was what we decided upon. We did online research and read many articles about preferred tank parameters, substrates, size requirements, food, etc.

We purchased a 40 gallon breeder, fine sand aquarium substrate (caribsea super naturals, one of the smooth grained sands for freshwater), a Fluval 206 canister filter, a heater, thermometer, aquarium driftwood from LFS, and a small power head for flow.
We cycled the tank first for six weeks, and use the API master test kit for freshwater to monitor levels. Ammonia and nitrites are at 0, nitrates below 10, ph is 7.0, kh is 3. We only use RODI water, and our water tests at 0 TDS. Tank temp is steady at about 75.6 degrees Fahrenheit.
The tank does have a few Amazon sword plants in it and some flourish tabs buried in the sand.
We could only find Corydoras Sterbai online through LiveAquaria. We ordered 10, as they should be kept in groups, and guessed that they would not all make it.
At first, we received a notification that shipping was delayed due to low stock. A few days later, we received a shipping notification. The fish arrived the next day and were immediately taken inside. One fish was DOA, but that was it. There was also one unidentified fish. All were in the same bag. All of the corydoras had very short barbels, and some were a bit red by the gills. We drip acclimated them for two hours, and all seemed ok at that time. A drop of Seachem prime was added to the shipping water to help with the ammonia present. After acclimation we moved them to the tank and left lights off for the rest of the day. In the morning, we turned the lights on, and one Cory was deceased. A few hours later, another one was deceased. Now, almost all are deceased, and are red around the gills. I have rechecked the water parameters several times today, and they have not changed at all. Ammonia and nitrites are still 0. The temperature has not fluctuated, nor the PH, nor the nitrates, nor the kh.
I do not see any external parasites and no bloated bellies. I did throw in a few sinking shrimp pellets the night before, and one sinking Hikari algae wafer. Nothing appeared eaten.

Yes, I am aware of QT and why we do it, QT practices, etc. I do practice QT for many things with my other tanks, but for this purpose I did not want to stress the fish out more than necessary and they will be the only tank inhabitants.

I have no idea what I did incorrectly. I had no where near this much trouble with my saltwater tanks, but I have always bought my fish locally, never shipped.

Any ideas? I do not want to buy more freshwater fish if I am going to kill them through my ignorance.

Thank you!

 

[Colin_T]

Hi and welcome to the forum

Without seeing pictures of the fish, my guess is the fish were in a weak state when they were sent to you and that combined with the stress of shipping, ammonia in the bag, and being put into a new tank with potentially different water chemistry, is killing them.

Newly imported fish should be held by the shop for a few days or more before being sent out so the fish have a chance to recover. If the fish came into the shop and were then bagged up and sent to you on the same day, it would stress them severely.

If there was ammonia in the bag, that would have knocked the fish about during transit.
2 Hours of drip acclimatisation for fish that are in a bag of water with ammonia is not the best. Floating them for 10 minutes to get the temperature the same, and then getting the fish into clean water is better than leaving them in water with ammonia.
Having said that, the fish could have been put into a couple of bags or had some Ammogon (Zeolite) added to the bag to help remove ammonia. And the shop should have fasted the fish for 24 hours before sending them out.

If your tank water has a different chemistry (pH and GH) to the supplier, that would also cause problems.

Remove uneaten food straight away so it doesn't cause ammonia problems.

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Photograph all the dead fish and the remaining live ones for evidence.

Contact the company that sent you the fish (by email) and inform them of the dead fish and ask for a credit. Include pictures of the dead fish.

Keep records of all correspondence to the company. If you telephone the company, write down the day and time you call them and who you spoke to. Write down what you spoke about, it doesn't have to be word for word but it's a good idea to make general notes about the discussion, just in case this goes to court. Hopefully it won't go that far but it's up to you and the company and possibly consumer protection. But contact the company first. Find out when the Cories came in and when they were shipped out. Inform them of the dead fish in the bag when you got them and the subsequent deaths since then. And ask if they will replace the fish.

In future, if you buy fish and have them delivered, have someone video/ film you unpacking the fish so if there are bodies in bags, you have video evidence proving the fish were dead in the bag when you opened the box.

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At this stage, just leave the lights off for a couple of days. Increase aeration/ surface turbulence. Keep an eye on the ammonia and nitrite levels and do a big water change if there is any.
Wait 24 hours and then offer the fish a bit of food but remove it after 10minutes if they aren't interested.

The following link has information about what to do if your fish get sick. It's long and boring but worth a read when you have spare time.
https://www.fishforums.net/threads/what-to-do-if-your-fish-gets-sick.450268/

The link below is the stress fish go through between leaving the fish farm and making it to the pet shop.
https://www.fishforums.net/threads/fish-importing-from-the-farm-to-the-home.451553/#post-3813924​

 

[Katov]

Thank you for your advice. I have left the lights off and continue to test the water- all parameters were still good this morning. I have also been removing the uneaten food- just not immediately. I increased aeration/surface turbulence last evening before posting. There are only two fish remaining. I will be contacting the company, which does have a guarantee policy, but I would not want to introduce any additional fish if there is something wrong with the environment.
Thank you for your help!

 

[Byron]

I concur with Colin. Your tank conditions are frankly near perfect for cories, so this was a problem with the fish/shipper.

My suggestion in addition to what Colin posted would be to only buy cories from a reliable fish store so you can see them in the store tank and take them immediately home. Cories are very sensitive and delicate fish, and really do not travel well at all. Not that most fish do, but cories are very "fragile" in this respect. And ammonia which will obviously accumulate in the shipping bag unless they added something to counter it will stress them severely. I have heard from store owners of bags of cories arriving with half of them dead. Purchasing cories from a fish store is better for the future. The shipper may replace them, or refund your money, try.