Certainly discus can be finicky feeders, which is why one cannot always feed live and/or frozen and expect their fish to accept a dense feed such as NLS. In many cases it becomes an all or nothing approach.
The fish that I posted photos of on page one were all started off on beefheart, as all Stendker discus are, as were every other group of juvenile discus that breeder imported, and all of them were converted to NLS pellets with little issue. Having said that, he fed no bloodworms, no beefheart, no live, or frozen of any kind. This is someone who had raised & bred discus for 20+ yrs, all on beefheart mixes, and decided that this time around he was going to take a different approach. Eventually all of his adult groups that paired off also bred like rabbits, producing tons of fry, and all on a diet of NLS. His fish room consists of 3,000+ gallons worth of discus tanks, so it's large enough to supply some good overall data as far as feed, growth, breeding, etc. One of the first things that he noticed is that when feeding a clean food such as pellets, there was no longer a need for daily water changes.
Even though many people still consider discus to be carnivorous, we now know that in the wild, discus are NOT a carnivorous species that require massive amounts of protein or fat for proper growth. Certainly, young juvenile discus require protein in the range of 45-50%, but that could be said about pretty much
every juvenile species of cichlid kept in captivity, including those classified as herbivorous. But as a cichlid begins to mature, their nutrient requirements in captivity change due to metabolic changes within the fish, and as this metabolic change takes place, so does their high demand for both protein & lipids.
Here's a link to a recent scientific paper that every discus owner/breeder should read.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-62252008000400008
"This species feeds predominantly on algal periphyton, fine organic detritus, plant matter, and small aquatic invertebrates."
"The alimentary canal of Symphysodon is characterized by a poorly defined stomach and an elongate intestine, some 300 mm long and 3 mm wide (in a 180 mm SL specimen). This intestinal morphology is typical of a cichlid with a dominantly vegetarian, detritivorous, or omnivorous diet."
Of course if one is in the business of growing discus out for resale, then the main goal (at least in many cases) is to get the fish as large as humanly possible, in as short of time frame as humanly possible. I think that a lot of discus would have much longer lifespans if people weren't in such a rush to have 6-7" inch fish. A poll taken a few yrs back on simplydiscus had the average lifespan of a tank raised discus at 4 yrs, which IMO is pretty pathetic.
Several years ago Chong et al ran a 3 month feed trial on juvenile discus (fish approx. 4.5 grams in weight) and concluded that a diet consisting of 45-50% protein, and 8% fat was ideal for optimum growth for juveniles of this species. I have no argument with those stats, and again the same could be said for thousands of other ornamental species of fish, but somehow this data has been used by certain segments of discus keepers to support their use of a high protein diet for semi-adults & adults. Where's the science to support that?
According to Heiko Bleher, his data matches those of the study linked to above.
What do Discus eat?
I have examined hundreds of specimens during many years and stomach and gut contents among wild Discus indicate an order of precedence: detritus, then plant material (flowers, fruits, seeds, leaves), algae and micro-algae, aquatic invertebrates and terrestrial and arboreal arthropods.
The Amazon has adapted to nature for fishes during millennia of evolution. Plants of the tropical rainforest have little water and cannot flourish during the dry season so cannot waste energy. The same happens to most freshwater fishes.
During the dry period, with a much reduced water level and hardly any food source except for predators many fish starve or feed on the little available, usually detritus.
Discus and many other fishes eat what they can get, but have to be constantly aware of carnivorous predators.
During the six to nine months of floods, almost all trees and bushes, flower and have fruits and seeds which is the main nutrition of roughly 75% of all Amazonian fishes.
The adults, and babies which grow to adults in that period, can then fill their stomachs and guts.
The carnivorous predators starve as they cannot find their prey in the huge water masses.
How much nutrition?
I have found the following percentage of nutrition in each one of the three species:
Symphysodon discus during low water: 55% detritus; 15% plant material; 12% algae and micro-algae; 10% aquatic invertebrates; 8% terrestrial and arboreal arthropods. During high water: 28% detritus; 52% plant material; 5% algae and micro-algae; 3% aquatic invertebrates; 12% terrestrial and arboreal arthropods.
Symphysodon aequifasciatus low water: 52% detritus; 18% plant material; 15% algae and micro-algae; 13% aquatic invertebrates; 2% terrestrial and arboreal arthropods. High water: 8% detritus; 62% plant material; 8% algae and micro-algae; 5% aquatic invertebrates; 17% terrestrial and arboreal arthropods.
Symphysodon haraldi low water: 39% detritus; 9% plant material; 25% algae and micro-algae; 22% aquatic invertebrates; 5% terrestrial and arboreal arthropods. High water: 6% detritus; 44% Plant material; 12% algae and micro-algae; 16% aquatic invertebrates; 22% terrestrial and aboreal arthropods.
A couple of things to keep in mind. Firstly the protein % found on all NLS labels are minimum values listed, not actual. Secondly I have seen adult discus eat the Grow formula pellets, so juveniles will certainly have no issue with smaller pellets, any more than any other species of cichlid does when offered smaller sized pellet food. With the smaller sizes of a discus mouth feeding small pellets is certainly not an issue.
As far as protein goes, one has to also remember that not all protein is created equally.
The protein percent on a label doesn't tell you anything about the quality of the protein, only the quantity of nitrogen that's been determined by someone wearing a white lab coat.
The value of protein is directly related to the amino acid content. A label % doesn't tell you how that protein was processed, or if it's even in a form that your fish can properly digest & utilize. As an example, feather meal is quite high in protein, but can be generally poor in overall digestibility. A fish food label could state 45% protein, but if only 60% of that protein is in a form that's available to the fish, then suddenly that figure on the label becomes somewhat meaningless to the average consumer, and their fish.
This is why I shake my head when I see hobbyists on various forums discussing protein % on various labels, as though Food A with 45% protein is somehow superior to Food B that has 35% protein on the label. The only protein that truly counts, is the digestible protein (DP) as in the amount of protein that can be fully assimilated by your fish.
This is not to say that there aren't other ways to get good growth & supply good overall health to a discus, but to state that one can't feed pellets alone & get the same results, is clearly not accurate.
