For anyone that has read some of the following info in a previous life, I'll apologize in advance for my verbosity.
I do, however, know that different species of fish would require different types of proteins, lipids, etc. For example the Tropheus of Lake Tanganyika being herbivores cannot process the same type of proteins that, say, a piscivore like a Pbass would require so specialty Tropheus foods are supposedly specifically formulated for their dietary requirements.
That's actually not true. All fish require the exact same nutrients, the levels of those nutrients will simply vary among various species.
This is the BIG lie that many manufacturers would prefer to keep hush hush. They want to sell you one of everything, as though each fish in your tank has very special individual dietary requirements. Obviously one can't simply come up with one formula for all situations, and all fish, but the whole "species specific" diet spiel has become ridiculous.
The vast majority of fish are opportunistic feeders, and are all omnivorous to a certain extent. Fish that are classified as carnivores don't just eat meat, any more than a fish classified as a herbivore just consumes vegetable matter.
The vast majority of wild fish are opportunistic feeders, and will eat pretty much anything that comes their way, and while
herbivores may in fact consume large amounts of plant matter, and carnivores may in fact eat large amounts of fish/crustacean based foods, that plant matter often contains certain amounts of nymphs, larvae, crustaceans, snails, mites, micro-organisms, and zoo plankton (protein/fat), and the smaller fish and/or crustaceans that the larger carnivores consume are typically gut loaded with phytoplankton & other smaller aquatic organisms (plant matter), so in actuality most freshwater fish consume the same
types of protein, fats, carbs, etc, just in varying degrees.
While a fish classified as a strict herbivore (such as a Tropheus moorii) may indeed spend its entire day scraping the aufwuchs, I can assure you that they would much rather eat a handful of worms if given the opportunity. In the wild they eat low quality foods because that's the only foods available, not because they choose to.
Their long digestive tracts are designed as such so that in nature they can break down the complex plant matter that they consume, which doesn't mean that they can't properly assimilate
more easily digestible forms of protein. This is a concept that many hobbyists fail to grasp.
Myself along with tens of thousands of other hobbyists have raised many species of fish classified as strict herbivores, such as Tropheus sp. on the exact same food as fish classified as piscivores, such as Cyphotilapia sp.
No problem.
A high quality pellet that contains a multitude of high quality raw ingredients will contain complete and balanced nutrition for ALL species, the only secret is understanding how to properly feed some of the different fish. You don't allow a fish such as a Tropheus to gorge themselves on a nutrient rich food, and for those that fall more on the carnivorous side of the equation you make sure they get a higher rate of food. Many frontosa keepers feed on the heavy side, but may only feed 4-5 times per week. Tropheus are better off being fed smaller amounts, more often. The key is reaching an optimum feed conversion ratio within each tank, and understanding that one has to meet the energy & growth requirements of the fish they are keeping.
The worse case scenario is that some of the amino acids (protein) may be excreted by herbivores, while the carnivores will utilize the majority of what's supplied. As long as the fat levels aren't overly excessive, Bob's yer uncle.
I told Pablo years ago that if he created a "herbivore" pellet (with large inclusion rates of seaweed, kelp, spirulina etc, he could make millions, and he agreed, but he wouldn't do it as he knew that in captivity this is not the way to provide optimum nutrient levels to a herbivore. To me that speaks volumes about the integrity of the man behind the food.
Others look at nothing much beyond numbers, and if there's a golden opportunity to meet a supply & demand situation, they will supply what the consumer wants, even if that consumer is uninformed & confused by the massive amount of propaganda and misinformation that has been perpetuated for many years in this industry.
Now we have companies selling 8 different formulas of food for freaking Flowerhorns. Again, WTF? You can feed a flowerhorn the same food that you feed any other cichlid, but as long as consumers remain ignorant there are companies that are cashing in, some of them, BIG time.
A formula to enhance the color red, one for shiny pearls, another for massive nuchal humps, etc-etc. A total crock of BS, but again, they are simply supplying a demand, and the shareholers ain't complaining.
For the past 40+ years, the owner of New Life has maintained ...... 120 ponds (approximately 30,000 gal. each), 1500 concrete vats (250gal.-500gal. each) and 1,000 40 gal. fry tanks on 2 five acre farms. A mix of cichlids that have been classified as strict herbivores, omnivores, and carnivores, including those classified as piscivores. and during this period every last fish on his farm ate the exact same food. No problem.
I mean even a cheap low cost bulk koi food can be fed to a piscivore, they simply won't be able to assimilate such a high carb diet as efficiently as a koi would. Fish do not digest carbs with the same efficiency as terrestrial animals. While it is true that even carnivorous fish are capable of producing some enzymes for digesting carbs, their ability to assimilate & fully utilize carbs is limited, unlike say a koi/carp, where 30-40% carbs can be utilized efficiently.
So while many "monster" fish keepers are fixating on protein levels, many miss one of the most important factors, that being the carb/starch levels in their food of choice. In today's market, with the cost of fish meal, krill meal, etc skyrocketing in price, many manufacturers are looking for lower cost terrestrial based plant protein alternatives.
But this is the land of MFK, where it seems that many hobbyists main goal is to grow BIG fish really FAST. The recent dog food topic is a prime example, some people see quick gains in growth & after that their eyes glaze over. The rest of the conversation just became a moot point.
Those are the people that fixate on little besides growth. And I am not pointing fingers at anyone that uses this type of feed once a month, so no hate mail please.
The largest freshwater carnivores in North America, Acipenser transmontanus (White Sturgeon), are raised commercially exclusively on pellet food that typically consists of 40-45% crude protein, and this species exceed both size & weight of the vast majority of tropical fish kept in captivity. Mature breeding (roe producing) adults can weigh hundreds of pounds, and be 7-10 feet long. Yet somehow there are those in this hobby that feel their pet fish (fill in the species blank) require more protein than a TRUE monster, kept in massive flow through systems such as the White Sturgeon. It's difficult for me not to LOL at that type of mentality.
MFK - woot-woot!
The whole fish "meal" is of lower nutrient value, or lesser quality, than whole fish type of logic doesn't exactly play out that way when you take into account all of the variables involved. Unless you are privy to the value of the raw ingredient, the exact inclusion rates, and the manufacturing process (including temps & durations used) you really have no idea which food contains better biological nutrient value or digestibility at post processing levels. Do dehydrated apples have no nutrient value? Of course not, yet this is how many people view fish meal, as though it somehow isn't quite as fresh or nutrient rich as other fish based raw ingredients. The reason that I posted that previous link is because neither of those authors have any vested interest in this subject, and both are considered experts in their field.
The reality is most labels provide a general guideline as to what's in the container, and not much more. Pet food is a multi-billion dollar industry, and most manufacturers hold their cards fairly tight to their chest. I realize that this can at times be confusing as well as frustrating to consumers, but no one is going to hand the competition their proprietary information on a silver platter.