Nutrition Basics
The key to choosing the right diet for your aquarium companions is understanding a bit about how your fish’s bodies utilize the nutrients you provide via your choice of foods. So let’s take a look…
PROTEIN: LIFE’S BUILDING BLOCKS
There’s a lot of confusion among hobbyists when it comes to protein. What are the correct percentages and what is the desired quality? The protein percentages on a fish food label don’t give you insight into the protein quality.
The value of a protein is directly related to it’s amino acid content. Amino acids include Arginine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Trytophan, and Valine. These are the building blocks of muscle, and the basis for growth. The protein’s source is a key factor of whether your fish can fully utilize the protein — or even fully digest it. Unless it’s fish digestible, the crude protein content on the label becomes somewhat meaningless.
High-quality protein derived from sources found in the aquatic environment doesn’t cause gastrointestinal issues even in fish considered nominally herbivorous. Excess is mainly excreted as waste. The source of bloat (or many other gastrointestinal issues) in these fish is poor quality protein that’s hard to digest and may contain components not useable by aquarium dwellers.
The best approach is to worry less about the crude protein numbers for either carnivores or herbivores. Focus instead on the quality of the sources — since that is the key factor for your fish’s health. The ingredients on the label are your first clue to the quality of the content. Avoid fish foods with too much grain (such as wheat middlings, corn, brans, potato flour). Likewise, avoid foods that use soybean-meal derived protein where possible. Instead, look for foods with high-quality, marine based proteins at the top of their ingredient lists: Whole Krill, Herring or other whole fish, squid, Omega-3 fish oil.
It’s a common misconception that all fish meal is a poor quality protein source. Fish meal can be an excellent source of protein, and rich in essential amino acids, fats, vitamins and minerals. The key is to only accept Whole fish derived ingredients. Lower quality meal derived from post-processing waste (i.e. heads, scales, tails and bones stripped of meat) have resulted in fish meals getting a bad rap.
If fish (or krill or similar) is not listed as the first ingredient, and the ash content is less than 9%, it can indicate too much soybean, wheat gluten or blood meal being used. While some fish, like Koi, can assimilate large amounts of these lower-grade ingredients, most tropical species cannot. Blood meal is high in protein, but is low in some essential amino acids such as methionine.
Obviously, it’s much cheaper for a manufacturer to use these lower-quality ingredients versus high-grade marine proteins like Antarctic krill, squid or whole fish. However, doing so is a critical ingredient for aquarium health.
PLANT MATTER AND VEGETATION
The source of plant matter is a factor in how well your aquarium companions’ digestive systems can utilize nutrients. One item to be aware of is cellulose, which is the source of fiber. While there are aquatic plants high in fiber — like fibrous Kelp (a primary food source for Abalone & Sea Urchin) — algaes and many of the microphytes that are common sources of vegetation in aquatic environments have little cellulose. Fiber should be fed in moderation. Fish can’t digest cellulose unless bacteria and enzyme actions take place inside the intestinal tract. Fiber is a laxative and too much will cause diarrhea. This in turn shortens nutrient retention time and allows insufficient time for the intestine to absorb nutrients. Some kelp or other fibrous plants in a formula is good, but moderation is key.
Aquatic versus Terrestrial Vegetation: Aquatic sources like seaweeds and algae are preferable for fish. They are simply better adapted to assimilate nutrients from these sources than from terrestrial plants. This doesn’t mean terrestrial plants are without nutritional value for the aquarium. Although less easily digested and utilized, terrestrial vegetables can provide valuable nutrients to your fish — particularly if aquatic sources are unavailable. In general, however, high quality foods will use primarily a variety of aquatic vegetation.
There are cases where specific non-aquatic plants can benefit your aquarium since they have properties not readily available in marine or freshwater counterparts. For example, garlic is a strong fish attractant. Likewise, studies have shown it to have both positive effects on fish immune systems and anti-parasitic qualities.
The bottom line: foods using a majority of algae and seaweeds are overall preferable to those primarily using terrestrial sources.
Many foods will tout spirulina or kelp as a selling point. This is particularly true with herbivore foods. When confronted with this, a look at the label is helpful; many so-called “herbivore” diets’ main ingredients will be fish meal or binder, a fairly small amount of spirulina, and green food dye to create the impression of a high concentration of algae. Spirulina (along with many seaweeds) is an expensive ingredient, and it’s not uncommon for brands to take this shortcut.
Vegetation variety within the formula is another consideration. Although spirulina or kelp are both useful nutrients, a diet consisting of a single plant source is not complete. Yet this is the route a number of food formulations take. A “basket” approach using a variety of seaweeds and algae (including spirulina) is preferable, as each provides different minerals, trace elements and nutrients for a well-rounded nutrition profile.
Spirulina: In particular, spirulina algae has been touted as the ultimate superfood, to the point that almost every hobbyist and manufacturer alike has jumped aboard the bandwagon. Most believe they need large amounts of spirulina in their aquarium diet — which isn’t the case.
Spirulina is indeed a high quality ingredient, and is very high in vitamin A and minerals. An inclusion rate of 5-10% increases growth rates and enhances blue coloration. However, vitamin A is a fat-soluble vitamin and excessive levels can be toxic in fish and can cause long-term health issues. It can also impart unnatural coloration. Most good fish foods already contain sufficient and beneficial amounts of spirulina. Feeding more than required is counterproductive.
In the next article, we’ll take a look at the role of carbohydrates and fat in an aquarium diet (hint: it’s not the same as for you and I)
BIBLIOGRAPHY & RECOMMENDED READING
Allahpichay, I. and Shimizu, C. (1985). Separation of growth promoting factors from non-muscle krill meal of Euphausia superba. Bull. Japanese Soc. Sci. Fish. 51, 945-951.
Berkman, P.A. (1992). The Antarctic Marine Ecosystem and humankind. Reviews in Aquatic Sciences 6, 295-333.
Finne, G. (1992). Non-protein nitrogen compounds in fish and shellfish. Advances in Sea Food Biochemistry. 393. Hemre & Sandnes (1999)Salmo salar.Aquaculture Nutrition (1), 9-16
Knox, G.A. (1970). Antarctic Marine Ecosystem. Antarctic Ecology Academic Press, London, pp 69 – 96.
Yanong, R.P.Y., Curtis, E., Russo, R., Francis-Floyd, R., Klinger, R., Berzins, I., Kelley, K., Poynton, S.L. 2004. Cryptobia iubilans infectiion in juvenile discus. Journal of the American Veterinary Medical Association 224:1644-1650.
Composition carotenoid pigments in the Antarctic Krill Euphasia superba. Nippon Suisan Gakkaishi.49:1411-1415.
Ako H., and Tamaru C.S. (1999) Are Feeds for food Fish Practical for Aquarium fish? Intl. Aqua Feeds 2, 30-36.
Fox, D. Biochromy. Natural Coloration of Living things. 1979. University of California Press, Ltd. London, England.
Miki M., K. Yamaguchi, and S. Konosu. 1986. Carotenoid composition of Spirulina maxima. Nippon Suisan Gakkaishi. 52:1225-1227.
Vinogradov, A. P., 1953. The elementary chemical composition of marine organisms (Efron and Setlow, translators), Yale University Press, New Haven, 463-566.