Backyard Aquaponics
A place to discuss aquaponics

Hello all,

To set the scene, I successfully grew out 15 trout last year in my ~1500L (pond liner) pond without a hitch, and have kept the pond cycled during the trout off season using doses of Charlie Carp to keep the vegie side of things going in my half IBC gravel bed (a very nice romanesco broccoli in the bed along with some lettuce atm).

The pond temp is currently between 14-17C and yesterday afternoon I received my 25 new fingerlings, but this morning a lot of them were dead, and by this arvo I counted 20 dead with the remainder looking not long for this world.

The usual culprit would obviously be ammonia/nitrite, but as I say the pond is well cycled, and I really can't see how 25 trout in the 80mm range and a small quantity of feed last night could possibly generate a lethal ammonia/nitrite spike over night in a 1500L pond.

Further to this, when I siphoned some solids out of the bottom of my pond about a month ago, I was happy to see a number of dragonfly larvae amongst the detritus, which are generally considered an indicator of good water quality.

I've seen my fair share of these type of posts, but this one has me beat... anyone have any clues?

Cheers,
Dr Love

Have you done an autopsy/necropsy on the dead fish? What colour were their gills? Were there any lesions/sores/marks? What was the condition of the innards? What about their eyes?

The surviving fish: are they gasping near the surface? Swimming up-side-down?

Is there any chance contaminants could have entered the system? Storm water run off etc?

Have you actually measured your quality? Ammonia, nitrites, nitrates, temp and pH?

What air system(s) do you have, or how do you aerate the water?

The solids you siphoned out: did it smell?

No matter what, you really should've tested for pH, Amm and N02, as a minimum, prior to putting the new fish in.

Depending on how much Charlie Carp you've been adding, and when, Amm and/or N02 may well be the issue... or your system pH may well have been dramatically different to that of the Trout farms pond and shocked the fish.

What was the PH of the water the fish came from? I lost 15 Barra fingerlings due to a 1.2 PH difference - within 24 hrs :/

I had to leave for three days a little over a month ago and a bunch of dead leaves got into my system. I came back home and found several dead fish. Some had Ick on them. I figured the dead leaves introduced the Ick and since I wasn't there I wasn't able to clean it out, fish started dying. Anywho, maybe you might want to check your system for trash or debris.

I was thinking fallen leaves too as its autumn. Not sure which part of Sydney you are in. But it worries me cause I have leaves in my system and I'm just about to get my trout. I can keep them out of my tanks but not out of the growbeds. What trees if any do you have around the tank?

I'd check back with the fish farm re their pH... most fish farms or suppliers I've dealt with (here in WA at least) tend to run their pH in the low 7's... about 7.2 - 7.4... going from a pH in the low 7's to a pH in the low 6's could definitely be enough to shock them IMO.

Where did you get you fish from?

Interesting in that you and Gran both have experienced mysterious and quick trout deaths and both had added Charlie Carp to the system!!

Very interesting, especially for the novice I am.
I got rid of all the water, rinsed the GBs heavily for about 3 hours, will wait a couple of days and then fill everything up with tap water, run it for a few days and then test the waters with 2 goldfish................If they stay alive, it might the CC...............or it might have been rainwater.............if not the IBC is the culprit because the oxygen levels weren't the reason.
I really learn how to be even more patient through AP

Does anyone know if introducing the trout from a relatively low nitrate environment to a much higher nitrate environment could kill them? This is my latest theory...

I have dumped out 80% of my water and will top up incrementally over a week or so (giving time for the chlorine/chloramines to gas off to protect my gravel bed bacteria) before I try again. Hopefully this will eliminate/dilute whatever the offending chemical may be.

Did you actually measured the oxygen level in the pond before putting the fish in?

You might have anaerobic bacterias active in the pond, due to the solids you left in from the previous harvest. The minimum aeration you have would then not be sufficient to support the new fingerlings.