Backyard Aquaponics
A place to discuss aquaponics

I raised Rainbow Trout (Oncorhynchus mykiss) from fingerlings for the first time last year. Although I managed to grow out 81/100 fish to the dinner plate, none were larger than 480g at harvest. It is has also been suggested to me that they were generally a bit on the skinny side. (Thanks, Troutman; I think your observation was that my fish had 'big heads'.)

This year I have been trying to achieve a more structured and disciplined approach to the feeding of my trout. For instance, rather than just feeding them a couple or three times a day (or every time I had a visitor), with an amount that seemed about right, I commenced roughly measuring the volume of the pelletised feed they got each day. This was achieved by using the same container as a feed scoop each time, eg a cup or jar, so that I had some constancy, and also some idea of the relativity of the size of one feed to the next.

I have now gone further and currently use a spreadsheet to calculate how much to feed the trout at each meal. My calculations are based on the number of fish and their average weight, and draw on researched feed rates involving body weight percentages. As far as I can determine the recommended feed rates are between 4% of body weight for fry down to 1% of body weight for adult fish. I have assumed that the adult rate applies at the age of two years, which is when the hens first produce eggs. Since hatchery trout are produced in Jun/Jul (here in WA, at least) I can assume that my trout are from a batch hatched this time last year, therefore are 12-13 months old, ie half way between fry and adult. If I graph a line between 4% and 1% and overlay it to a trout timeline then, by my calculations, my trout should currently be receiving about 2.5% of their body weight in (high protein) feed per day to achieve optimal growth. I have calculated an average weight for my fish based on the weights of a few fish netted and weighed, and the total number of trout that I believe to be in the tank. I have not included the three Silver Perch, nor the three Marron, that also inhabit the tank, in feed calculations.

I am currently feeding at less than my calculated 2.5% rate for the following reasons:

- there are a few significant assumptions in my calculations so I choose to err on the side of conservatism;
- my system is untested at its current stocking level;
- I have yet to bring online recently constructed and installed GBs. Basically, my biofiltration limit is unknown.
- skinny live fish are better than plump dead ones;
- I can increase the rate, as necessary, when better information and more accurate data become available.

I am feeding my trout Skrettings Spectra 7mm pellets. The feed conversion rate is 1:1 for high protein feeds, so apparently for every gram of food eaten, a gram of weight is gained by the fish. (I find this hard to believe but I have come across the same figure many times, so now just accept it.) My spreadsheet calculations take account of the expected increase in mass of the fish with each feeding and adjusts the figures, accordingly. I am hoping that regular weighing of the fish to get an updated average of their weight will not be necessary. Besides, if I 'randomly' scoop out three fish to weigh at feeding time I can't be sure that I am not catching the biggest and greediest fish that will only serve to skew my weight average.

My method is to carefully weigh the day's calculated ration of feed using a set of quality digital scales purchased for the task. I split the ration into two and containerise and label it. I aim to feed in daylight hours, with a minimum separation of feed times of 8 hours. A small amount of feed is thrown in initially, to confirm the fish disposition. Once the fish have shown themselves to be actively feeding (aka 'going ballistic') the rest of the meal is thrown in, ensuring as large a coverage as possible. This is aimed at allowing the smaller, less greedy fish to get at least some of the feed.

Note I haven't factored in the insects consumed by my fish each day - how can I, unless I take steps to reduce the amount to zero?

I invite comments, criticism, confirmation of approach, support of assumptions or their replacement with facts, etc. I don't claim to be an expert in this area but am very keen to increase my expertise.

It will be interesting to see your findings as the year progresses, PJ.

Bookmarked.

If you want to get technical there are feeding rate tables available that will show you how much to feed for the different sizes of fish in relation to the water temp. In general the amount of feed will increase as the water temps rise (up to 18C max). ie you would be feeding 5 times more feed at water temps of 16C than you would at temps of 2C.
Fry are generally fed up to 10% body weight per day whilst fully grown fish 0.6% at average growing temps. A fish of 100 - 200gms only needs to be fed 1% of its body weight per day.
I have kept records of my feed inputs and worked out the FCR's every month in some years. I have never achieved a FCR of 1:1 over the winter months but found I could achieve it over the spring months.
I think at the end of the day what you hope to achieve will govern how much you feed your fish. I have been selling 450gm plus trout into the local restaurants for over a month now so there is no reason why your fish couldn't be this size or bigger (I have mine at a much higher stocking rate than yours). On the other hand if you are going to try spawning with them next year I wouldnt be letting them get too big as stripping a 2.5kg fish is not as easy as stripping a 1kg one.

Water temp - another consideration to factor into my calculations! Thanks, Troutman.
As far as 'fully grown fish' are concerned, fish of all types apparently are never fully grown but continue to grow until death. The longest lived Rainbow Trout is believed to be an 11 year old specimen that weighed close to 22kg , although sea-run Rainbows (Steelheads or Ocean Trout) are claimed to grow larger. Whilst this one clocked up a few years, most Rainbows only live 4-7 years, and even less in Australia it seems. That is why I settled on 2 years as my 'adult' age for calculation purposes.

My fish are between 100 and 200g so, at a 1% of body weight feed rate, I may already be overfeeding them! This is a tricky business.

I don't intend to attempt to grow-on trout to adult size. The summer heat up here is ferocious and I reckon it would be an expensive and risky exercise trying to keep large volumes of water cool enough for them. I hope to try keeping fry through summer, though, if I can keep any of my alevins going. My first attempt at hatching eyed trout eggs was, shall we say, a character building and time consuming learning experience.

This might help you with your egg raising experiences, PJ.

http://www.troutintheclassroom.org/teac ... p-timeline

I have quite a whirlpool going in a circular tank 15/45, the trout are given quite a work out. (theres a stumpy one who always likes to lead the pack, or maybe its coming last...dont know. ) Would this affect the feeding rates and growth? Would it affect the eating qualities?

Too strong a current might result in excessive expenditure of energy... but as long as they can drift off into quieter water...

Then it's entirely beneficial... for growth.. the energy expended...promotes feeding.... and protein & muscle growth, rather than fat...

The corollary... is low flow circulation tanks... and/or over-feeding... produces couch potatoes.... fat/obese fish...

Went out for dinner in Bunbury on Sunday night and a friend ordered Ferguson Valley Trout, thought they must have been Troutmans. By the way Gav, she loved it..

I feed mine 6 times a day this time of year and as it warms up and the daylight gets longer I increase to 8 times. I prefer to feed smaller amounts more often and I usually feed around the 2% mark. I can only do this due to the automatic feeders.



I also have lots of swirl in my tank to keep it clean and the Trout swim effortlessly through it. I must admit my tank bottom is much cleaner this year with the increased stock levels.
Not sure what the 15/45 refers to?...I'd like to think that an active fish is much happier / healthier than a lazy one.

Muzza

Haa, good to hear Muz.

Skeggley, there are recommended flow rates/water speeds for trout raceways that would probably have some relevance to your whirlpool situation. I have had a look but can't find the particular reference but, as I recall, a water speed equivalent to between 0.5 and 1.5 of the fish's length per second was the recommended target speed. Faster than this made the fish work too hard, which presents problems, and slower introduced a range of other issues related to oxygenation, waste removal, etc which probably don't apply in your system as they would in a typical trout raceway.

I will post the link once I find it.

Thanks, Charlie. I read it last year when DunderOz linked to it but couldn't find it again when I could have really used it a few weeks ago. Anyway, I still have some sac-fry swimming around so all is not yet lost with my trout babies.

Not true PLJ, many of the Silver Perch I use for breeding are kept in cages and the sex and weight of each fish is recorded for future reference. Most of these fish are 5 plus years old so less than half way thru their expected life span yet every year when I catch and weigh them they are pretty much exactly the same weight as at the same time the previous year. Also, Brown Trout particularly tend to lose condition and therefore weight when they get into the last few years of their life.



The Rainbow in my avatar is the world record caught for the species, cant remember the weight but it was around 22kg and a triploid. The current state record for Rainbow Trout in WA is also a triploid fish.


That depends where they are, in Tasmania Rainbows have been recorded to 10 yrs of age but in WA not many even make it to 4 yrs old as it seems that the heat takes its toll. At 2 yrs of age Rainbows are sexually mature so in feeding tables regarded as being fully grown fish.

IGFA World record for Rainbow Trout (Oncorhynchus mykiss): 21.77 kg (48 lb 0 oz), Sean Konrad, Lake Diefenbaker, Canada, 5 Sep 2009 (source)

AAA (WA Div) State record for Rainbow Trout (Salmo mykiss (Synonym)): 3.525 kg (7 lb 12 oz), Peter Fragomeni, Pemberton, 6 July 1996 (source)

I don't think a Western Australian Rainbow Trout capture will challenge for the world record any time soon.

Thats right. Peter is actually a good friend of mine.

Muzza 15/45 is probably the timing for the pump. 15 minutes on and 45 mins off.

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