Backyard Aquaponics
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Hi everyone, I've lost three fishes for the first time. The rest are at the bottom lethargic and there was one swimming slowly at the top when I pulled the three fishes out (Two were dead and last one belly up and remaining at the bottom). The one that is holding on to dear life is in a quarantine tank with a tablespoon of epsom salt and plenty of oxygen.

Water parameters Ammonia 0.5ppm, Nitrite 0, Nitrate 0. Those are normal water parameters for me with ammonia usually around 0.25ppm.

The only thing that changed two nights ago was BTone and light mist of neem oil last night. I'm scratching my head on this one but I presume a parasite problem causing brown lung disease. Does anyone know appropriate salt to fish tank ratio? Fish tank has adequate oxygen too. Any input would be much appreciated.

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What's BTone?

I'm assuming it's Bacillus thuringiensis.

Brown blood disease is caused by high Nitrite in the water, so if your Nitrite level is 0.0ppm and you haven't had a spike recently, then you can probably rule that out. What is the water temp and pH, are you heating the water?

Also, instead of epsom salt, the surviving fish would likely do better with sea salt at 1gm/Ltr.

_________________
Mr Damage - a.k.a: Yabbies
Owner at Perth Aquaponics - Aquaponic Consultant & Trainer
Trade certified Horticulturist & Cert IV TAE

Yes correct. BTone as the bacteria used against caterpillars.

Thanks for your reply guys. I really wish I could use this as a learning experience but I really dont know what has caused this fish death at this point.

pH was at 6.0 last night which is expected prior to my weekly buffering. There were no pH spikes recorded previously but temperatures did drop bc of a sudden change in weather.

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Sad day in my humble aquaponics journey and what bugs me the most is that they probably suffered a slow death and not knowing where things went wrong. The others look like they will die also. Plants will in turn suffer

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I did a salt water bath treatment for 3 mins with oxygen and put fishes back in the tank. They dont look like they will survive though.

How does one introduce new fishes to the system after this mass death please?

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How is the water temperature doing now? I know back in June you were having troubles with the fish when the water temperature was low. This is an outdoor system and you mentioned the weather suddenly cooling off. Cold weather may have caused problems with the biofilter as well - possibly caused a spike in ammonia or nitrite which you didn't know about.

Is that right? I was not aware that this could happen. Temperatures did drop about 4 nights ago especially at night bc of a tropical depression.

How often does one need to check for ammonia and nitrite? Would it be a good idea to do so during temperature changes in the weather? And so I'm wondering how does one protect fish in an outdoor system?

I have been doing some research:

A) Temperature drops promote parasitic and fungi infections

B) Some aquaponic practitioners use a refractor to test salt in water and will add 3g of salt/L of fish tank water as preventative measure and help fish against osmosis also. I wonder how often one should do so?


My fish death remains a mystery though. I see no slime or traces of parasites/ redness/unnatural lumps on my fishes. I understand the pinch of losing fishes in our system now. I was actually planning to purchase some materials to build an overhead shelter today but that was gut wrenching to see them suffer and die like that. Going forward I'm not sure how to reset the system either.

Also,what sort of problems does temperature drop cause in bio filter please?

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I doubt that these deaths are the result of a disease or parasite. Usually mass die offs like this are from environmental stress of some sort.

Filters are biological systems so it makes sense that they would also be affected by cold temps. Filtration slows down with the temperature and your feeding should as well. Sometimes in Fall you'll also get an algae die off (assuming you have enough algae) that will cause an ammonia spike if the filter isn't working well enough. Over time though, the filter organisms will adapt to the conditions you have and will provide a better buffer against these sorts of problems. They still won't do much ammonia conversion at low temps (below 50F) but ammonia is less toxic at low temps so it generally works out. Most fish don't feed a lot with temps below 55F.

You didn't say how cold the water got. Most Tilapia species start to die somewhere around 55F but are stressed under around 70F.

For an outdoor system like this you'd probably be better off choosing a species that suits your climate. Trout do well in temps below 74F but die when water temps go above this (that probably gives you long enough to get them to eating size if you buy them in the 6 to 8 inch size - I figure you have about 9 months at least)(in hot weather the ground water will still be cool enough to lower your tank temp if necessary). Yellow Perch do well up to about the mid 80's and Bluegill do well at pretty much any temp but grow slowly compared to most. I don't know which of these is legal for you to stock or how large the system you have is - I'd probably go for Yellow Perch or Trout in your situation.

Salting your system is a good idea. I usually suggest 1 part per thousand. This helps with stress, building a slime coat and nitrite toxicity problems. I'd salt when you setup the tank and anytime you change the water or a large portion of it. Just add the amount of salt you need for the volume of water that you added. I don't salt when I top up because of evaporation.

Thank you again for sharing your knowledge.

Regarding water temp, it would not have gone under 60F. I lost the last three of my fishes that I had nursed for over a year this morning. I had a closer look by moving them in the water today and I found a very subtle film of slime here and there on them.So I suspect fungi correct?

I'm scratching my head as to how that forms in the water? Is it because part of my system is exposed to rainfall that trickles over some rocky structures and a metal sheet that I use to shelter my sump tank?

Where things may have gone wrong:

1) I had placed fingerlings in a neglected isolated tank where I noticed that they were dying. So I moved the last two into my Sump tank. Perhaps they were infected? But would their small bodies have been enough to transmit that fungi into my AP system?

2) Temperatures did drop starting last Sunday where fish became lethargic and I reduced feeding. I didn't see then rubbing themselves against the tank of anything though. However they remained idle at the bottom of the tank.

3) SLO cuttings had clogged a bit causing water level to rise over the T connector. I noticed some biofilm in the SLO piping as I pulled it out and gave it a good spray.

May I ask how you guys what is the safe procedure in order to introduce new fish to my system? I run a humble blue barrel CHOP2 system but plants are thriving and I would like to learn and get back up from this sad anecdote.

I am currently looking to purchase a refractor and reckon that I will add salt to my system periodically once it gets going again. The most accessible fish for me at the moment is koi which I will probably purchase from a friend. Trout or perch are not available here.

Thanks again. Much appreciated

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I took a second look and the slimy film I was talking about in my previous post is barely noticeable. I'm not sure if they would have been producing more mucous that adhered to parts of their body from the salt treatment and as they were dying. I wish I could say for sure that fungi/biofilm may have been the cause but I analyzed the last three dead fishes and it was not a striking difference. All the 20 dead fishes did look healthy. Perhaps something that clang to their gills may have been the cause? Still scratching my head

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I’m sorry to hear that your fish have died. I believe neem oil is toxic to fish and other aquatic animals, so may have been a factor in the loss.

I don't think the slime indicates any kind of parasite/fungi. Fish always have a mucous slime coat.


You say the system is small and that the temperature dropped fairly suddenly to around 60ºF. I don't think you have any reason to suspect any cause other than temperature. The lower limits of temperature tolerance for some tilapia might b below 60ºF, but this all depends on acclimation - they have to have time to adjust.

"I will add salt to my system periodically once it gets going again" - The salt doesn't go anywhere, so if you do this it will accumulate unless you are exchanging water.

The metal roofing you mention could cause fish to die if its galvanised with zinc, water runs off it and zinc accumuates in the water to dangerous levels for the fish. Having said that, this is probably not the case as fish die off wouldnt't happen so suddenly, but rather bit by bit over time.

I really don't think you need to keep scratching your head! The temp drop is enough to explain the issue.

Koi will surely do fine at your temps. But the better you can insulate the system and reduce temperature fluctuation the better for the health of any fish species. Just increasing overall water volume would help.

One thing to bare in mind is that fish are generally in contact with potential pathogens all the time, and when they are in good health they will generally "win the battle" against pathogens. However, when fish are stressed their immune system is compromised and the balance is tipped in favour of the pathogens. In aquaculture fish have nowhere to go to escape environmental changes, so the environment needs to be kept optimum for their health. Even mjor viral outbreaks, in the shrimp industry for example, usually only occur after sudden environmental changes such as temperature and salinity drop...

So its not so much about keeping pathogens out, but rather about keeping conditions optimum so that fish are free of stress and thus capable of "winning the battle" against pathogens.

Sorry about your fish, its always sad to lose them.

Good luck!

Hi danny, I really appreciate your input. And so the tilapias' immune system was compromised due to the drop in water temp which caused them to die in batches like that to some pathogen.I didn't know that temperature had such an adverse effect on tilapia but after reading your post, that of others and some research on the internet I have learnt a valuable lesson going forward. It's a reminder that I still have so much to learn and mistakes will be made time and time again.

I'm hoping that I will have better luck with a larger size system and kois.

Would you discard all the water from the system and start over with a fishless cycle? Plants are still going strong.

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I probably wouldnt discard all the water. Unless your metal roofing is galvanised, then i'd get rid of half maybe and change the set up to get rid of the galvanised metal run-off.

A break of a week or two might be a good thing just so that any kind of pathogen, that may have proliferated in theperiod of time that the fish were struggling, subsides again.