3. Fish Food – Aquarium Science

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.

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.

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.

Fish Food in General

A major concern for most fish keepers is what is the best food for their fish. Most “normal” commercial pelleted food made for fish today is excellent, so it is difficult to go wrong when feeding fish, contrary to popular mythology. There are two exceptions to this. Most of the commercial “veggie” foods analyzed and some of the flake foods analyzed had too low of a protein level to be considered “good” foods by the author. But note this is an “OPINION“, unsupported by the research.

What is far more important than the type of food is the amount of food. The biggest mistake beginners do is to over-feed their fish. The directions on the food are ridiculous. “two to three times a day an amount they can eat in two minutes” is WAY too much food. Fish are cold-blooded creatures and only need small amounts of food once a day.

Feed ONLY an Amount of Dry Food Equal to Two Eyeballs Once Per Day

If this rule is followed almost any food will be fine for fish (six fish equals twelve fish eyeballs).

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 didn’t change with levels less than these “optimums”.

Here are some popular fish foods.

Ingredients	1	2	3	4	5	6	7
Fillers, Grains		24%	36%	33%	37%	39%	74%
Fish meat	33%	25%	16%	16%		20%	25%
Insect meat	33%
Shrimp, krill		50%			37%	40%
Vegetables Algae	33%		47%	50%	25%
Nutrients
Carbohydrate	21%	20%	29%	37%	27%	27%	35%
Protein	40%	39%	43%	35%	38%	45%	35%
Fats	5%	9%	7%	4%	5%	10%	4%
Ash	10%	13%	10%	10%	11%	8%	13%
Fiber	13%	8%	2%	5%	6%	3%	3%
Moisture	10%	20%	9%	9%	12%	5%	10%
Cost price per 450 grams	€ 23	€ 19	€ 14	€ 10	€ 21	€ 13	€ 8

Top Fin Pro Series Crumbles
New Life Spectrum Probiotics
Top Fin Color Enhancing Pellets
Hikari Cichlid Staple
Xtreme Pewee Aquatic Pellets
Cobalt Aquatics Shrimp Pellets
Hikari Cichlid Excel

Green = best food
Yellow = not optimal for breeding
Blue = slightly negative effect on any fish
Red = not optimal for juvenile growth
Purple = food we cannot recommend

This chart is best looked at by adjectives:

Green is superb
Yellow is excellent
Blue is good
Red is good
Purple I cannot recommend

The green shaded foods meet all criteria for all fish. Avoid the yellow shaded foods if you are breeding fish (low fat). Avoid the blue areas for carnivores if you want the fastest growth (too many vegetables). And the red areas have too little protein for maximum juvenile growth.

Neolamprologus caudopunctatus Orange Fin

Fish Food Myths

There are a huge number of myths parroted around social media about fish foods. Some of these myths are:

The type of food fed to fish is critical to success in the hobby.
Different types of fish (herbivores, carnivores) can’t be kept together because they require different foods.
Feed fish only what they can consume in five minutes.
Mbuna get “Malawi bloat” when fed high protein food.
“Just like us, fish enjoy a varied diet”.
Live foods are the best foods for tropical fish.
Animal protein has an inferior nutritional content compared to plant protein.
There is such a thing as “high quality” and “low quality” protein.
Chicken, tilapia, and beef are bad foods for fish.
Fat is bad in fish food
Krill, bloodworms, and tubifex worms are bad for fish.
Mbuna are herbivores and eat only plants.
Some fish require live foods.
Wheat, corn, rice, oats, and potatoes are good foods for herbivore fish.
Fish will starve before eating a fish food they don’t “like”.
Fish like some garlic in their food