While I personally wouldn't feed either of those brands to my fish, there's a few common misconceptions about some of the ingredients that need correcting.
However, it's pretty obvious that fish meal (mostly left over bones after the good meat is stripped off for human consumption) cannot be as nutritious as whole fish.
Probably the biggest misconception in the hobby.
Not all fish meal is made from processing plant leftovers (waste).
There are many types & grades of fish meal, while some are indeed made from leftover processing plant waste (such as white fish meal) others are comprised of whole fish, such a herring meal. There are low ash fish meals, fish meals with high ash content (excessive scales & bones), low temp fish meals where the vast majority of nutrients are left intact, and even
fertilizer grade fish meal. (yes, it's used as fertilizer!)
Not all fish meals are created equally, and the wholesale price will typically determine the overall quality.
A good read on the positive attributes of fish meal in aquaculture diets, written by R.D. Miles, Professor, Department of Animal Sciences, and F.A. Chapman, Associate Professor, Department of Fisheries and Aquatic Sciences; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
http://www.thefishsite.com/articles/200/the-benefits-of-fish-meal-in-aquaculture-diets
Some of the leading experts in the science of fish nutrition believe that there are growth promoting factors found in fish meal that have yet to even be determined by the scientific community. The bottom line is, the biological value of a quality fish meal is quite high.
Grains, binders, and low cost fillers.
Some starch/carb content is not an issue in a fishes diet, and in most cases cannot be avoided to some degree. Wheat flour is a very safe binding agent, there only becomes a problem when excessive grains/carbs/starch are utilized in the feed, as most species of fish can only assimilate so much starch. While a carp/koi may be able to utilize as much as 30-40% carbs, most species can only assimilate in the 20% range, with some carnvivores falling into the 10% max range.
When feeding low cost generic foods with excessive grain content, not only does much of what goes in, come right back out the other end, if too much is consumed at once these types of feeds can also cause gastrointestinal issues in some species, such as those that are prone to float and/or bloat.
(eg. fancy goldfish, Tropheus moorii)
Also, there is a BIG difference between terrestrial based plant matter (such as soybeans, peas, etc) and plant matter from aquatic sources, such as seaweed, kelp, spirulina, and various micro-algaes. The former contain known anti-nutritional factors, which can inhibit growth, and cause other health issues if used in excess, or if not processed properly. (such as at low temps.
More on that subject can be found here:
http://www.uoguelph.ca/research/publications/Assets/HTML_MAGS/oasis/nutrition3.html
To state that one should only feed what is
natural to the fish, makes little sense for most people that are keeping fish in a glass cage. In the wild fish don't eat frozen seafood, either. They don't have to be concerned with B1 deficiencies from Thiaminase issues, and those that consume prey in the wild are also consuming the stomach contents of those prey, which in many cases consist of numerous phytoplankton and/or zooplankton.
I think that if one was to keep a colony of tropheus moorii in captivity and offered them nothing more than algae, you'd soon find out that tropheus require far more than algae to keep them in optimum health. This is where the amino acids found in raw ingredients such as krill meal, herring meal, squid meal, shrimp meal, etc come into play. The same amino acids, and fatty acids, found in the insect nymphs and larvae, crustaceans, snails, mites, micro-organisms, and zoo plankton, that this species consumes when grazing on the aufwuchs.
Their long digestive tracts are designed as such so that in nature they can break down the complex plant matter that they consume in massive quantity, which doesn't mean that they can't properly assimilate
more easily digestible forms of protein.
The vast majority of fish are opportunistic feeders, and are all omnivorous to a certain extent. Fish classified as carnivores don't just eat meat, any more than a herbivorous cichlid just consumes vegetable matter. There must be a reason why many of the larger piscivores found in the wild contain enzymes (such as amylase) that are capable of breaking down carbohydrates.
It's all about balance, and in some cases feeding what appears to be a more "natural" diet, may in actuality fall far short of some of the higher quality commercial foods on the market.
Not knocking anyone who goes the cheaper route & uses low cost alternative feeds, not everyone can afford to feed their fish high end commercial food, or fresh/frozen with vitamin supplements.
Just wanted to clear up a few of the comments made in this discussion.
