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Protein Quality

Crude Protein

On many foods, both for Humans and animals, the nutrient composition often contains things like "Crude protein", "Crude Fat" and "Crude Fibre". The word crude in this context refers to the method of determining and calculating the component referred to.

Protein contains about 16% Nitrogen. It is not the only thing in food containing Nitrogen, but normally it is the main one. Crude Protein is simply the percentage of Nitrogen multiplied by 6.25.

The phase "Crude Protein" does not say anything about the quality of the protein.

Protein Quality

Protein is made up of Amino acids. There are several different types. There are about 22 sorts commonly encountered. The exact number included depends on what organism you are considering.

A high quality protein is one that contains all the essential Amino Acids in the correct proportions. Frequently animal proteins are of higher quality than plant ones, although both animal and plant proteins vary a lot.

I am a vegetarian, but I eat eggs and milk which both have very high quality protein. Vegans need to be more careful to balance their diet, both to include enough of all the vitamins, including vitamin B12, and to have all the Essential Amino Acids in it.

Essential Amino Acids

An "Essential Amino Acid" is one that the animal cannot make by itself from other Amino Acids. As you can see the actual number of essential Amino Acids varies with different types of animal. Humans have 8 Essential Amino Acids. I think Horses have 10 Essential Amino Acids.
There are many different sorts of Fish and their Amino Acid requirements vary with the type.

Biological Value

This is similar to Protein Quality. Note that the quality of a protein can often be improved by adding a different one. A very common example is when a meal has both a grain based food and a legume. A couple of common examples spring to mind. Beans on toast has bread, made mainly from Wheat, a grain, and Beans, a legume. Another one is rice with peas.

As a general rule, a variety of food is better than just one.  This applies to fish and other animals as well as to people.

Fish Food

A good quality fish food will have more than 20 different ingredients. In Australia, there was once a fish food made that had only 5 different ingredients. It was no good, and a lot of people had trouble with it. The company that made it makes some excellent products of other sorts, but clearly had not done enough research into the nutritional requirements of fish.

Some other fish foods may also only contain a limited number of ingredients, but are much better than the fish food mentioned in the previous paragraph.  These foods are generally not suitable as the only food for your fish, but can be a valuable part of a varied diet.


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