Bluefin wrote:
How do i calculate the correct amount to feed them?
... 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...
Quote:
At the moment i am feeding them two tablespoons three times a day.
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 ...
Quote:
There is a fine silt/ delitrious material on the bottom of the fish tank, that gets disturbed when the fish feed there.
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..
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