Backyard Aquaponics
A place to discuss aquaponics

I came back from 10 days away to find all but 2 of my silver perch had died. Given they were 3 years old and some of them were plate sized I'm completely gutted.

Anyway I've been trying to work out what happened and have the following theory which I'd like some feedback on....

I checked the fish and the water the day I left and everything was fine. I had previously been told not to feed the fish when going away rather than relying on an automatic fish feeder. Apparently silver perch could go a few weeks without feeding without a problem. None the less I asked a friend to drop by and feed them a couple of days after I left and she mentioned that they were ravenous.
8 days later I returned home to one hell of a stink, check the tank and discover 30 fish in various states of decomposition. One of the fish had been completely mauled. I tested the water and discovered the ammonia was off the charts whilst ph and nitrates was in the normal range. I rang my friend and asked her how much she fed them the day she dropped in and she reckons she gave them 2 teaspons worth, not a great deal.

My theory as to what happened was that after a few days without food the bigger perch set upon one of their friends, and munched him up. Then being summer he's floated around the tank decomposing releasing large amounts of ammonia which has then killed off the other fish.
Does that sound likely?

Nup.... Silvers just aren't aggressive like that and they will be fine for a couple of weeks without food. Very hard to know what may have happened without being there, but that is the least likely explanation. Could have been something like a power outage perhaps?

IMHO - if that was the case, then your theory may be correct, but with the possibility of it dying from unknown cause and then being attacked..

Otherwise - how do we explain the mauling in the first place, unless it was another animal eg. a cat , what done the murder and mayhem...

I would go along with Silvers being non aggressive, for my witness of hundreds in purging tanks, await their fate as someone's dinner.
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Would have been an easy catch for any animal if they were up by the top in near death condition. If they didn't make it out of the tank they may have just been too large for whatever found them.

but, we really don't have the critters that might do it in Oz.

Surely only a cat, that could take a swipe, unless an open FT and birds-of-prey got cheeky with no humans around..

I have a friend with KOI who has lost some big fish to eagles..
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It'll remain a mystery

I've not fed my fish for well over a month before and they were fine, trout and silvers.
My thoughts would be along EB's lines, power outage or perhaps one of the fish died and caused an ammonia spike.
How big is the ft? How big are the gb's?

The tank is 1200 litres with 1200 litres worth of grow beds. I don't think a cat or bird would have got to one of them though as I have a lid covering the tank. I take your points though that SP aren't agrresive so wouldn't have turned on each other. Perhaps one of them just decided to keel over of natural causes...

Oh well back to the drawing board I suppose.

Rather than starting again from scratch with fingerlings I wonder if I could restock it with adult fish?
Have you guys ever tried it?

I noticed golden ponds in Baldivis sells full sized silver perch so perhaps I could just get a couple of big uns from there?

where abouts in perth are you and when were you away, there have been several power outages that I know of recently.

I've stocked with adult fish, though it can be expensive - what do GP want for each fish? I may have a few spares as I'm a bit over eating them!

I got fish from GP a couple of weeks ago, tanks were feral as usual, checked a few fish over in the net though and besides some damaged fins due to being manhandled they actually seemed fine (unlike the Barra fingerlings). two weeks in quarintine tanks and all made it into the system 5 days ago. $6 for 5-6 inch fish, $8 for 7-8 inch, and i think $12 for the largest size

they're reasonable prices.

Loosing fish after 3 years is gut wrenching, I feel for you.

is it possible that something toxic got in the FT?

during my week of absence one gold fish got its tail mauled but was still alive.

but they were fed daily by a friend.

also I have noticed with the warmer weather the SP are ravenous.