Backyard Aquaponics
A place to discuss aquaponics

Another dozen trout netted out today, only one more lot to come out to end the season in this system. All a decent size with the biggest one at 37cm, 653g and 580g after gutting

Congratulations. How much longer will the system with the chiller run? You must be logging the power used for the AP compared to the house. The company I work for is upgrading some of our remote WiFi towers including mine with data logging. I can't wait to see how the little system I threw together from bits and pieces eight years ago performs.

There's no doubt that AP energy usage for both AP systems in summer is much more than household use, although I'm not it logging separately, as it is all run from one electrical system. Just the chiller alone can use up to 20kWh on a hot sunny day.

I'm going to try to keep the big system running over summer until I get some more fingerlings in late Feb or early March. Getting them a month or more earlier will save me a fair bit of money. I'll have to harvest all the big fish before then, as the big ones will probably eat the fingerlings. I'll put all the fingerlings in the big chilled system, and transfer 100+ to this system when hte water cools down enough in April, or perhaps March if it isnt too hot.

We pulled the last of the trout out late yesterday, I dropped 2 of about 400g each into the larger system (via quick ~50m runs with them in the net) and processed the rest. The ones I gutted averaged 510g, the biggest being 669g, and 582g gutted.
I've developed a new system for handling them- round them up and catch them in the net. Hold the net in the water and then tickle them into submission, then lift them up when they are calm, then whack on the head. It is much easier to dispatch them than when they are thrashing around trying to escape!

[quote="Gunagulla"]........ tickle them into submission, ....../quote]

As Pauline would say.. "please explain" ..

I wonder if that is what I found last week, with my silvers.. same situaltion.. in a floating net and after a time with my hands under, trying to catch, they actually settled down..
Naturally, they were all going crazy, trying to get throught the bottom of the net, and my hands were under them..
.

Just holding them from underneath and tickling their tummy calms them right down, so much so that I can lift them out of the water and they don't struggle at all. It makes it much easier to aim the special tapered rolling pin I use to whack them on the head.

A chef friend help herd them into the net and we gave him one- his opinion is that it tasted better than ones that were put into cold water immediately after catching and then whacked on the head a short time later, while they were trying to thrash about and escape.

There are Rainbow Trout in Thailand and after reading your thread.....

Yea, I expect the stress from thrashing about stressing for a time before being dispatched would have an effect on the flavor.

I can't really give a good side by side account for comparison but I know when we subdued channel catfish with CO2 before cleaning the cook was less stressed since trying to handle a thrashing, slippery 5 lb catfish with barbs can be challenging (and catfish require a really hard blow to the head to stun them.)

FYI we learned that a chunk of dry ice in a bin of water is pretty darn effective and fairly quick at knocking out channel catfish, I expect it might be even quicker/more effective on trout.

After Toll "Priority" (is that a joke name?) finally delivered my parcel, 10 days after it had arrived at their Tamworth depot, I had my Zinc test kit. It did take a phone call from my supplier to the Toll area manager in Sydney asking for the the sacking of the person responsible for not delivering the parcel for so long, but finally, it has arrived.

This is a very expensive test kit, but will measure the concentrations of Zinc that APers are interested in. Top of the scale is 1.4ppm, and the first test I did was of the tap water, some of which had been in a gal tank at the shed, was off the scale. It is hard to extrapolate a graduated colour chart, but I'm guessing in the 2ppm range.
So the question is, what do you dilute water with, to bring it into scale I caught some stormwater overflowing the gutter last night, that should be zero ppm, (alternatively some demineralised water would do) so today I'll measure the water in this AP system, which only has 1 Murray Cod in it now.

The scale resolution is 0.2ppm from zero to 1.4ppm, so with 1 in 2 or 1 in 3 dilutions if required, I should be able to determine how much zinc is present. The kit includes a water conditioner that can eliminate any Copper contribution to the readings, not that there will be much of it in the AP water, as it hasnt been through the household Copper pipes. I have found a couple of other potential sources of Zinc though- my water pump has a 90deg 40mm gal bend, used instead of a poly elbow, to reduce friction. I also had some clamps holding netting or air cell insulation on GBs, the shiny gal coating on the clamps is now rusty, so no doubt some of the Zinc coating has gone into the water. There is also a brass one-way valve on the house pressure tank, so a miniscule amount of metal is no doubt getting into the water from that too.

it sounds like compared to my 2 2500l gal tanks, which only rose the zinc to 1.8ppm, you are in the "wouldnt even worry" territory, unless you are filling from that gal tank at your shed.

Some of the water in the system has come from the 22500l gal shed tank - no choice when that's the only water available. I'll collect a sample shortly and see how it looks.

Is there a ball park threshold for zinc in aquaponics? Or is it dependent on the fish species?

From my research (google), it is more dependent on species than I expected, in the area of 2-3 X as high for some species than others.

lots of info to be found using search terms such as -species or common name- (heavy) metal toxicity

Recent replantings in GBs, and the removal of the insulation on top of the GBs, has resulted in a marked increase in diurnal water temperature range, and increased max temp (yellow plot). Now that the trout are gone, this isn't a problem. I added a bit of Seasol this morning, something I haven't done for months. I'm hoping this system will tick over satisfactorily mostly on fish poo reserves until I introduce a new batch of trout in autumn.

I've just done a Zn test, and it appears that there is under 0.5ppm Zn in the system water, which is good news.

The water in the house tank ATM however, is at around 3ppm Zn, it mostly came from the 22500l gal tank at the shed. I think I'll tip a pile of shell grit into that tank, to reduce the rainwater acidity, and reduce the amount of Zn being dissolved by the water (aka very weak Carbonic acid).