Backyard Aquaponics
A place to discuss aquaponics

greeting afishanados
I have 150 silvers in my fish tank and i have 2mm sinking fish starter. How do i calculate the correct amount to feed them? I have had them two weeks, they seem to be contantly hungry. At the moment i am feeding them two tablespoons three times a day. They range in size from 60mm to 90mm. Should i just keep feeding them untill they are not interested in anymore or is it better to feed them once a day? They have eaten earthworms and seemed to be keen for them.

I find that feeding them a few times a day when tiny is a good thing. Feed them enough so that they are still a tiny bit hungry, they will clean up after themselves better that way.

... aren't you lucky BlueFin.... one of the assignments I've done over the last week was "Optimize Feed Uptake".....

I'll precise it for you....


The amount you feed your fish daily is usually worked out on the basis of a percentage of their body weight...this is known as the feed ration....

Research on Silver Perch, from the Grafton Research Facility, has found that they generally require between 1% and 10% of body weight per day ...


Very small fish may feed at the higher rate and larger fish at the lower rate... generally small fish have a greater need for higher protein/nutrition than larger fish... and tend to convert to growth proportionally faster....

For example, at 26 degrees, a one-gram Silver Perch may feed at 10% of it's body weight per day. Whereas, at the same temperature, a 500 gram fish may feed at 3% of its body weight per day...


Temperature is the most critical determining factor in your feed rate...

Metabolic rates approximately double for every 10 degree rise in temperature... this means a fish will use twice as much oxygen and energy, and require twice as much feed at 30 degrees than at 20 degrees...

One of the reasons why Silver Perch seem to feed much better at temperatures above 20 degrees.... they also convert feed into growth correspondingly faster above 20 degrees...

Hence we feed much more as temperature rises...


So... Firstly Bluefin... work out your feed ration....

This is determined by the percentage feed rate for your water temperature...(see below)... Mulitplied by the bio-mass of your fish tank ....

The bio-mass is the number of fish multiplied by their average rate...

If you look at the "Sliver Perch Length vs Weight" graph thread... you'll find that a 70mm Silver Perch is about 7 grams in weight....


Let's average your fish (60-90mm) to say... 70mm ....> 7 grams each.... So 150 fish times 7 grams => 1050gms of biomass in your system....

Now consult the table below (from "Silver Perch Feeding Strategies").... for the correct feed rate... (%/day) for your water temperature and size of fish...




So... lets assume your fish tank is 22 degrees... you should them be feeding at 3% of body weight (feed rate)....

So your feed ration is 3% of your bio-mass.... in your case 3% x 1050gms...

So you should be feeding a daily feed ration of 31.5 gms of feed for the day... split over 2 feeds...



I weighed out two tablespoons.... at about 30gms.... your total daily feed ration....

And you're feeding them that much three times a day.... ....

No wonder ...



You're just wasting feed Bluefin... one, even if they do eat most of it (and Silver Perch will overeat)... they'll excrete most of it, and burn energy trying to process it...

And two... as temps increase the fish will consume more oxygen as their metabolism increases anyway... more oxygen to process the feed... while uneaten feed will consume oxygen from your tank....

All at a time when, because of temps.. your water will have less oxygenation capacity anyway....

And three.... it's just costing you money in wasted feed...

Ease of the feed mate.... ... they'll go back and pick/clean up the stuff on the bottom later anyway... as Jaymie suggests..

thanks heaps rupe,
that is just the info i have been searching for and you explained it so concisely and in a manner i can understand Ill knock back the feed. The ammo is staying at about .05 but he nitrate has jumped to 10. I might get my super syphon out and clean up the bottom. I have just been worried that ill suck up my fish.
thanks again rupe

betcha silvers at 40 deg wont eat twice as much as at 30 deg

but seriously, what rupe said

IMHO great info worthy of a sticky

+1.
(Especially since I just some myself)

....from me too Rupe.

I must be reading this wrong? I've got 14 Silvers and the average sized one weighs 67g so using the above page and working on water temps being over 24 degree I've worked out the feed rate to be 67*0.05*14 which is 46.9g feed 2x per day??? That seems way too much

67g x 14 = 948g total fish weight
1% of is 9.5g total for the day
Lets say 5g per feed twice a day

But if you have enough filtration then feed twice a day till they stop feeding

ahh ok just realised you are doing 5% so yeah, the figure is what you said but thats total over the day