Insignificance of Fish Food Selection

3.1. Insignificance of Food

A Caveat : Protein Level in the Food

The most important variable when choosing a fish food is the protein level. The higher the protein level in any food the healthier the fish. But this effect is NOT because eating high-protein food is good for a fish. Rather the effect is due to what high-protein food can do to the ecosystem that is in any aquarium. Higher protein food is a significant factor in creating crystal-clear water. In turn, crystal clear water gives very healthy fish.

Oscura heterospila
Oscura heterospila

Low-protein food does not directly produce unhealthy fish. Rather its effect is indirect, through a long line of causal effects:

  • A low-protein food has a high carbohydrate content
  • Carbohydrates are only 50% digested by the fish
  • The undigested carbohydrates create dissolved organic compounds (DOCs) that have a high carbon-to-nitrogen ratio
  • Pathogenic bacteria and other pathogenic organisms proliferate with high carbon-to-nitrogen ratio DOCs
  • The proliferation of these organisms in the water column results in “dull” or even slightly milky water
  • These pathogenic bacteria and other organisms in the water column attack the fish

Now everyone wants to know what defines a low protein food. I make the cut-off at 45% for dry commercial fish food. But the “45% protein” level is completely arbitrary. In truth, there is a continuum between 30% and 60%. A level of 42% protein in the dry commercial fish food won’t be “ideal” but it also won’t be that bad. The key is the clarity of the water. Is the 42% protein food giving crystal clear water? Or is it giving “dull” water or even slightly cloudy water. There is a “threshold” here.

Otopharynx lithobates – Orange Blaze
Otopharynx lithobates – Orange Blaze

But where the threshold will be is very dependent on a multitude of variables. For instance, 34% might give crystal clear water in one aquarium setup while 52% might give “dull” water in another aquarium setup. Note that if I must buy commercial fish food, I ALWAYS buy the highest protein level I can find.

Below I will discuss those food variables that directly affect the fish This is with the clear understanding that all these effects are minor compared to the effect of the protein level on the health of the fish via the creation of a pathogen-filled water column.

Otopharinx sp. Spot - Sani
Otopharynx sp. Spot – Sani

Fish Food Quality

Research has shown little or no effect on life expectancy or the health of the fish with various fish diets. There are four slightly desirable characteristics only:

  • For optimum juvenile growth rate, have over 40% protein
  • For optimum fertility, have over 10% fat
  • For optimum juvenile growth rate, have less than 30% cheap protein from the likes of soybeans or gluten.
  • For optimum growth rate in juveniles have “whole fish” or “fish meal” as one or more of the first few ingredients in fish food.

But it must be emphasized that this is all relative. Fish do just fine with food that is outside this range. All of the research found differences in the growth rate of juvenile fish and the fecundity of fish with foods at less than these levels. But the survival rates of the fish didn’t change with levels less than these “optimums”.

It should be noted that commercial tropical fish breeders in Florida buy their feed from commercial feed manufacturers who produce dry fish food in twenty-pound bags that meet the four levels above. These foods (save for the Purina feed) are not available to the home hobbyist.

Petrotilapia sp. Chitimba Bay
Petrotilapia sp. Chitimba Bay

Quantity of Food Fed

The other reason for flexibility in food has to do with the quantity of food fed to tropical fish by hobbyists. Virtually all fish kept by hobbyists are fed a diet that has two to five times the food content of what the fish would be eating in the wild. Because of evolution and niche selection by species, fish in the wild live “on the edge” when it comes to food. In nature, there is fierce competition for food resources and each fish has evolved to survive on a very narrow band of specialized food input that is typically either quite low or very cyclic.

Placidochromis johnstoni
Placidochromis johnstoni

Fish Types and Food Requirements

Take a typical Malawi Hap. This Hap may have evolved to eat largely midge larvae in Lake Malawi, making him an “insectivore”, a type of “carnivore”. His food “input” per week might be 0.5 grams of animal protein and 0.1 grams of animal fat from these midges. His body has evolved to use this resource at its fullest potential. And many of his species don’t get this minimum input and thus don’t survive. This is simply Darwin’s “survival of the fittest” at work. If this Malawi Hap is given ONLY 0.5 grams of vegetable protein and 0.1 grams of vegetable fat from something like spirulina, the fish might well have health problems.

Now put this fish in an aquarium and feed him a “herbivore” diet of spirulina pellets that give him 3 grams of vegetable protein and 0.4 grams of vegetable fat per week. This is six times the protein level of the native environment and four times the fat level. This fish will still prosper, despite being fed a “herbivore” diet. The aquarium is an artificial environment where the harsh rules of “Mother Nature” often don’t apply.

Herbivores, omnivores, and carnivores ALL do well on just about any diet from cheap flake and pellet food which is low in protein (~40%) and high in carbohydrate (~40%) to ground-up fish fillet that is 75% protein and 7% carbohydrate. There does seem to be a benefit from a vegetable or other source of roughage added once a week or so (something like “zucchini-a-la-fork”) but that evidence is anecdotal.

When it comes to vitamins and minerals none of the twelve book references (compendiums of literally thousands of research papers on fish nutrition) used for this article found any need for extra vitamins or minerals in any decent food for fish. All these references clearly said that virtually all the commercially available tropical fish foods will be just fine for any tropical fish, largely because of the large amount of food available in an aquarium at even 1% of a fish’s weight per day.

Paracyprichromis nigripinnis – Blue Neon Albino
Paracyprichromis nigripinnis – Blue Neon Albino

The “Best” Commercial Fish Food

Now every fish owner wants his fish to be in the best health possible. But research has shown little or no effect on life expectancy or the health of the fish with various fish diets. There are four slightly desirable characteristics only:

  • For optimum juvenile growth rate, have over 40% protein
  • For optimum fertility, have over 10% fat
  • For optimum juvenile growth rate, have less than 30% cheap protein from the likes of soybeans
  • For optimum growth rate in juveniles have “whole fish” or “fish meal” as one or more of the first few ingredients in fish food.

The protein level is more important than the fat level. But it must be emphasized that this is all relative. Fish do just fine with food that is outside this range. All of the research found differences in the growth rate of juvenile fish and the fecundity of fish with foods at less than these levels. But the survival rates of the fish and their health didn’t change with levels less than these “optimums”.

Vieja maculicauda – Lago Izabal
Vieja maculicauda – Lago Izabal

Here are some popular fish foods.

Ingredients1234567
Fillers, grains 24%36%33%37%39%74%
Fish meat33%25%16%16% 20%25%
Insect meat33%      
Shrimp, Krill 50%  37%40% 
Vegetables, Algae33% 47%50%25%  
Nutrients       
Carbohydrate21%20%29%37%27%27%35%
Protein40%39%43%35%38%45%35%
Fats5%9%7%4%5%10%4%
Ash10%13%10%10%11%8%13%
Fiber13%8%2%5%6%3%3%
Moisture10%20%9%9%12%5%10%
Cost price per 450 grams€ 23€ 19€ 14€ 10€ 21€ 13€ 8
  1. Top Fin Pro Series Crumbles – not optimal for breeding
  2. New Life Spectrum Probiotics – not optimal for juvenile growth
  3. Top Fin Color Enhancing Pellets – slightly negative effect on any fish
  4. Hikari Cichlid Staple – slightly negative effect on any fish
  5. Xtreme Pewee Aquatic Pellets – not optimal for juvenile growth
  6. Cobalt Aquatics Shrimp Pellets – best food
  7. Hikari Cichlid Excel – food we cannot recommend

We need to emphasize that this difference is not very large. For the yellow areas (less than 10% fat) the testing of fish only saw decreases in the fecundity of fish (egg and sperm counts) and no difference in health or survival rate.

Placidochromis elektra
Placidochromis electra

More Information

To see the science behind the above conclusions go to this link:

3.1.1. Fish Food Science

Many people want the “best possible” commercial dry food for their fish, even though research says it isn’t needed. So, an analysis of commercial fish food is in:

3.6. Commercial Dry Fish Food

If one wants to 100% control what their fish eat, one should use gel food. This is reviewed in this link:

3.4. Gel Fish Food

For those wanting more data on the many myths about fish food click on these links:

3.7. Banned Fish Food

The myth of a correlation between high protein diets and Malawi Bloat is examined in this link:

3.8. Food and Malawi Bloat

Metriaclima fainzilberi Luwino
Metriaclima fainzilberi Luwino

Startpage Aquariumscience

Source: Aquariumscience.org – David Bogert

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