Backyard Aquaponics
A place to discuss aquaponics

Hi All,

Sorry to be asking this, as I know it has probably been asked before, but I have searched and searched and have not really found the information I am after, i've even looked in scientific journals and the like!

Basically what i'm after is a feeding chart that specifies what percentage of feed per unit body mass rainbow trout should be fed. I know this is a big ask, because this varies with temperature, and with age, so there are a lot of variables to deal with!

From what I have read, it is anywhere between 3% and 10% for fingerlings, and then down to 1%-3% for older fish.
Basically, I have no idea!

Anecdotally, I am currently feeding my 200 rainbow fingerlings 5g every two hours between 8AM and 10PM, which totals 40g per day, and there is a very slight amount left over at each feeding, but not a great deal..
At the last weighing, the trout were around 2g, so this means I am currently feeding 10% by biomass daily.
Temperature is 19deg today as well.. so many variables!!

Additionally, it would be great to get some idea of the FCR for rainbows, because then the entire picture can be put together, and I can model growth rates and the like

I hear it's in the proximity of 1.5-2:1?

Any thoughts would be greatly appreciated

Cheers,
Nic

http://www2.ca.uky.edu/wkrec/TroutFeedsFeeding.pdf

There you go

In Europe they are getting FCRs of 0.8:1 and you lose your licencse if you can not maintain an FCR: of 1:1 or better. In Australia the common figure quoted is 1.2-1.5:1.

Where abouts are you Nic?

With trout that small what are your plans to get them through summer?

Thanks very much, that's exactly what i'm after!

Is that's true regarding FCRs in Europe, or are you pulling my leg? :p

I'm in Northern Victoria, on the Murray somewhere :p.

That is the main concern, but, we do have a bore that we pump around 10k L from daily (or more) in summer for irrigation, and this water comes out at 18deg.

So I'm thinking we'll pump from the bore to a head IBC mounted on a stand, then this can drain down to the IBC with the fish in it throughout the day, keeping it cool. Then pump from there back to the main tank .

Also have a 60L/min air pump which should help!

Thanks again for the help

Yes and no. Yes its true, no I'm not pulling your log.

It is a combination of excellent stock and feed management coupled with their efforts to improve their genetics through selective breeding.


That will help a lot. I'm assuming that your system will be outside?

Good luck.

Wow that's great, pretty impressive too!

Yeah it will be outside, but we'll shade and insulate the IBCs.
Last summer the absolute maximum the main tank got to was 26deg, which I know is pretty lethal for trout, but we should be able to moderate the temperature much more easily in a smaller tank

I had my trout to 26 last summer.

At that temp it is not the temperature that kills them but rather the lack of O2. No feed and lots of air got me through. Mind you it was only about 6hrs during one day at the end of a 5 day heat wave. I imagine you might have warmer temperatures more often and for longer.

Shade and adding cool water will help more than insulating but it can't hurt. Better than shade would be reflective cloth because it reflects the energy from the sun where as shade cloth stops and absorbs it.

Speaking from memory, it was around 26 pretty often, but didn't get much higher than that due to the thermal mass of all the water. The daily fluctuation with the ~30kL is around 1 degree.

Reflective cloth is a good idea, we'll have to look into that.

I've ran the numbers from the above feeding chart, and see that trout should get to the 500 gram mark within around 6 months, all things going well. Is this in line with what actually happens?

I tired to attach the excel document, but the type isn't allowed. Let me know if you want me to put it on google docs or something

Good to know that the trout survived the 26 degree days.. what did you use for aeration?

Bear in mind that you won't be able to feed much while the temperatures are high. Over 20c the trout will still be hungry but as the temperature climbs the amount of feed that will kill them goes down. As far as I know it is not the feed that is the problem but the increase O2 demand from the metabolism of the food and the increased O2 demand from the biofiltration.

Above 22 and even above 24 they still may be feeding heavily but you will be entering dangerous territory if you satisfy their appetite. This means you will need to restrict their food during the hot weather which will slow their growth rate down.

For aeration I just had an air pump. Bear in mind though that the altitude hear is 750m and we are on the cusp of the divide. Just the other side of the hill to the north only 10mins away it is a lot warmer and my setup would likely fail there.

On the other hand it is in a GH.

I think everything begins to work against the trout at 22 plus, i've read they still feed heavily, but stop metabolising the feed and just excrete some of it, which causes extra load on the filtration, and further decreases the O2 supply in the water. So there's a bit of a vicious cycle there!



Yeah I think i'll do my best to keep that temp down, and not feed anything above maintenance when the temp is above 22.



Sounds good, I think i'll set up a few failsafes for aeration, with maybe a gravity backup to ensure the O2 supply is sufficient. Do you think the GH moderates temperature much?

Not really. If anything it can do the opposite. Because I don't have any automatic climate control it generally just makes the GH warmer for longer. For most of the year this is a very good thing for me.

I guess without wind chill when I close it up over night it doesn't get as cold but a single skinned GH is not very insulating so I don't think it makes much difference. What makes the the difference is the higher temps during the day and the large thermal mass of my system.

I've been thinking more about the water temps and my trout now it's warming up.

Do you think the 60L/min (max 30L/min in each IBC system containing no more than 1k litres of water) air pump I've got running would be enough to keep my trout happy? That's in addition to the water falling from the GB's.

Water temps aren't a problem yet but no doubt as the warm weather settles in things will be a bit different.

I think the idea is to maximise DO in the water, which means providing maximal aeration, as well as minimising anything that can reduce the amount of DO in the water - like fish waste.

I don't think anyone can make a judgment though, unless they know how how many trout you have, and how big they are.
What temps do your tanks get to in the middle of summer?

Yeah it's a bit of a vague 'piece of string' type of question I know.

No idea what temps my tanks get to over summer as they aren't a year old yet, they were set up towards the end of Autumn this year (May-ish). There are now 8 trout in one tank and 10 in the other of varying sizes, the biggest about 30cm long. Chances are by the time the warm weather really kicks in those ones will be long gone though, lol.

It will be interesting to see what happens as things really warm up, all I can really do is watch them and check to see how they are coping. I'm just hoping the water doesn't get too warm too quickly so the smaller fish have a chance to grow a bit more.

Not a call I'd make any time soon.

Without a DO meter you have to over engineer.