Backyard Aquaponics
A place to discuss aquaponics

I am struggling to narrow down the cause of death for my father's Silver Perch in his aquaponics system. There were approx 80 in our 950L tank, which have been growing nicely for the past 18 months. There have been very limited causalities, up until around 4 weeks ago.
Now I'd say there would be less than 10 left alive in there. They share the tank with Rainbow Trout, which are also dying, however at a much slower rate.

I've taken the water levels today. There have been no dramatic spikes in any of the levels for the past few months (levels recorded weekly). However, Nitrate I think may be subject to misinterpretation.
Temp= 16 degrees
ph= 6
Ammonia= 0
Nitrite= 0
Nitrate=
My father has been recording it as 40-80ppm, however the results I looked at today looked a little more like 80-140ppm. We did a second test, and we still couldn't agree on the levels. We both agreed that the colour result was a very bright cherry red, instead of the varying degrees of reddish-orange indicated on the chart, if that helps. Dad thinks it's still 40-80. The plants are and always have been thriving beautifully.

I've been studying the DPI pdf documents, and they seem to share symptoms of just about every fishy-ailment out there.
I have attached a link to some pictures which are a sample of what I retrieved this morning (I was unable to upload them. Gremlins). There looks to me as a slight mottling along the lateral line. This appears on most of the dead fish.
What appears to be either ulcers or some form of abrasion, also along the lateral, only appears on a few of the fish retrieved today.
The gills in the last picture picture are a far more vibrant red/swollen to the naked eye. However, this doesn't seem to be present on many of the fish retrieved.
All the fish are very slimy and have a thick layer of mucus, however being that I don't know how "fresh" they are, I've been a little hesitant to attribute this to their deaths.

https://www.facebook.com/media/set/?set ... 113&type=3

I have also included some pics of the system he uses. I have no idea of there are any variables there, but it's worth a shot, just in case someone out there notices something about the set up that might be creating some kind of unbalance.

Thank you!

Hi Hungry,

I can't view your pics, but I can say that 80 SP's, especially at 18mo, is a lot for 950L of FT... way too much... plus you've got X? amount of Trout on top of that.

What were the Amm and Nitrite test levels before the fish began to die 4 weeks ago?... I would've at least expected to see some Amm constantly present with that many fish in your 950L system. The Amm and Nitrites may have been high a few weeks ago, with the resulting health issues showing now.

How much GB volume have you got?

How much air have you got pumping into that FT?

Also, it's my understanding that mixing Trout and SP's is not good practice

Yep.... That's a lot of fish...

Mr D has asked the pertinent questions....

Way too many fish. They are being stressed to death by a combination of fish overload and mixing with trout.

Looking at the Facepuke pictures... you appear to have an IBC with two bath tubs as growbeds.... about a total of 400L...

If that's the case... then you should only have 20 fish in total... maximum...

Which by the sounds of things... is probably about what you've got left.... nature is trying to tell you something....

Sorry to be blunt... but you don't have enough filtration, or oxygenation... for even your original 80 Silver Perch... let alone any trout....

Who suggested that you could stock that many fish???

Try diluting your test sample to get a better result (50% fish tank water + 50% tap water, then times your result by 2).

Good idea , but nitrates are not the problem here. Or maybe they are as there must be a lot of ammonia produced to make a high level of nitrates in a mature system.
Adding trout would make the ammonia shoot up, and the trout feeding would stress the silvers that would be not wanting to feed. All bad
Over stocking to the max

Thanks guys! He's been following the advice of someone he knows who introduced him to aquaponics a few years ago, in addition to advice from a local aquaponics store. I'm not sure which information he got from where, however.
Overcrowding seems so obvious, now that it's been pointed out. I know silver perch can grow slow, but these guys seem to be tiny considering the amount of time he's had them for. The trout were a suggestion I think from his buddy, plus he was getting impatient with how slow the SP were growing. The trout were added about 3 or 4 months ago. This is all making so much sense! I know very little about aquapoincs, but seriously, overcrowding should of been up there with "mysterious disease" from the start!

There are three baths, there is also pvc piping (halved lengthways) along the top of the set up where he plants smaller herbs. Those pipes are currently empty, which I think accounts for the higher nitrate (assuming we're going with my interpretation of the reading).
I've just suggested he invest in two more tanks to off-set the high amount of fish, which I think will also make it easier over-all to manage. He seems to be forever flushing the whole system out, for reasons beyond me.

So if he adds another two 950L tanks, separates the trout and decreases the amount of perch per tank, we might find the system running more efficiently? He's just about to ship the whole get-up out to their retirement property, where they have three more baths waiting to add to the system. Watch this space, I feel like this is just the beginning of a very one sided relationship with this forum.

RupertofOz- Natural selection! Of course! I feel like this answer couldn't of been more obvious if it had slapped me in the face! Massive face-palm/head-desk moment. Thanks! haha!

Separating the trout out to another tank will help and the addition of 3 more growbeds will help a lot. Fish stocking has to relate to the amount of filtration you have in the system, ie, volume of growbed media.
Work on having a MAX of 3kg of fish per 100L of growbed and this is for a mature system not a new one. I personally stock to less than this to be safer.

Sounds like he's fallen victim to the "1 fish in 10L" nonsense that's floated around...

At least he, or via yourself.. is now in touch with people who can provide real help and advice...



OK, with three baths... nominally 200L each.. a total of 600L..... 30 fish is the maximum stocking...

The high nitrates are due to the amount of fish waste being produced... number of fish and feed... and lack of plants to remove them... consistant with lack of grow bed area..



That's probably the best idea... no idea how many trout he has... but if he puts 40 Perch in each tank... he'll need at least 4 bath tubs per system for filtration...

And if there's abouit 40 trout... then that system would be better with 5-6 bath tubs...



I would advise that he just sets up his system correctly.... posts to the forum, takes our advise....and grows some fish out for a year or so successfully...

pics don't load for me

And I forgot to add before.... make sure you have an air pump on each system....

Your problems, besides overstocking.... are almost certainly related to oxygen depravation...