Aquarium Nutrition: Part 2

AvatarBy John D Hirsch MD 5 years agoNo Comments
Copepod - reefs

“Copepodkils”. Licensed under CC BY-SA 3.0 via Wikimedia Commons

Acute starvation has many causes, but always occurs when metabolic demand exceeds ingested food energy and triggers the conversion of stored nutrients. Both sugars (carbohydrates) and proteins (amino acids and peptides) store approximately 4kcal/gm. of tissue. Fats can provide as much as 9kcal/gm.  Lack of adequate food or poor quality food along with injury, infection, infestation and stress all contribute to acute malnutrition.

So what happens in acute starvation?  Carbohydrates (sugars) are rapidly converted to CO2, water, and energy. In general, animals store little energy in the form of carbohydrates; in humans, for instance, there are around 900 calories stored as glycogen (a storage form of sugars). These are rapidly depleted. Protein production slows as proteins are redirected and catabolized for energy producing NH4 (ammonia), CO2, water, and energy. In many animals ammonia is converted to less toxic urea and excreted in the urine. In fish, approximately 90% of the ammonia is excreted as ammonia via the gills. The remaining 10% is converted to urea and excreted ultimately through the kidney. The higher metabolic processes are affected first. As you can see in figure 2, even with all-natural foods, more than 60% of the ingested protein is either lost during digestion or catabolized for energy, leaving less than 40% to sustain life. There is a significant energy cost to processing nutrients.

As the indigestible/lost portion of the food increases, the amount available for sustaining life decreases digestion become more inefficient and energy-expensive to acquire those same nutrients. Critically, both mucous production and immunity are affected early in the process. Loss of the protective mucous coat leaves fish and corals vulnerable to attack and loss of immunity only worsens that situation, healing of wounds effectively stops, as they become super-infected with organisms that typically are not pathogenic in healthy individuals. In addition, the highly metabolically active cells of the digestive tract slow absorption and packing of nutrients for transport to distant cells only worsens the situation. At some point, not well-defined, acute starvation becomes irreversible. Some organisms have adapted to periods of low nutrients, others not so much. Corals, for instance, are like small farmers, and keep a “garden” of zooxanthellae for low nutrient times. Smart.


nutrition absorbtion chart - reefs

figure 2

Here are my recommendations for healthy all natural nutrition; I am borrowing and slightly amending some of the recommendations of one of my favorite authors, Michael Pollan (The Omnivores Dilemma and In Defense of Food) and biomimicry.

Feed Food, not processed nutrients. An example of processed nutrients is fish solubles.

Fish solubles are produced as a by-product of the fish canning and the fish oil production industries.  Almost any fish can be used. The whole fish (menhaden, herring and other algae-eating oily fish) or more likely discarded fish parts (from tuna, salmon, cod, squid, etc.) are partially cooked, and then placed into a hydraulic press. The liquid produced is centrifuged to remove the oil (which contains the majority of the essential fatty acids), and the leftover water is then condensed or dried to produce condensed fish solubles or dried fish solubles. What is left in the press, including dried bones, skin, and body parts is fishmeal.

Fish Meal is Fish Meal regardless of the source.

If there are more than 5 ingredients, it is not food. Here I am not speaking of the excellent mixtures of frozen all-natural foods but single-sourced processed nutrients with additives. Why would you add supplements to food unless it was deficient?

If you cannot pronounce an ingredient, it is likely not food.

If you do not know what an ingredient is or does, it is not generally food.


Read the labels on food products.

There is a difference between dry weight and as delivered information.

The first five listed ingredients represent the majority of the product. If a product is 99% water, what are you buying?

If you see any or all of the following in the first 5 ingredients, it is not food for marine inhabitants. These are indigestible complex carbohydrates from terrestrial sources. A sample list:

Starches, including rice, corn, and wheat

Flours, including rice, corn, wheat, and wheat germ

Glutens, including wheat and corn

Soybean meal and byproducts



Potato in any form

Gel Binders

Fiber, both soluble and insoluble

For single-source food products, heavy metal testing is inexpensive and should be on the label. The cost of testing the 5 metals listed below from a commercial food grade lab is about $100. The recent scare in the industry was (fortunately) unfounded, but let’s be clear, all heavy metals are toxic and they are accumulated in animals as they make their way up the food chain. Look for packaging with this information.

  1. Mercury
  2. Lead
  3. Arsenic
  4. Cadmium
  5. Antimony

Feed a little as often as possible. A good rule of thumb is that all food should be consumed in about 2 minutes. Aggressive feeders and timid feeders need to be identified, and attention given to all inhabitants. How often is often? It depends on your definition of health.  In nature, most of our tank inhabitants are grazers, and the configuration of the digestive tract will give you clues about feeding.  Next to the gills, the gut is the receiving dock for the nutrients and waste elimination. The gut is divided up into 3 basic parts: the foregut, the midgut, and the hindgut. The foregut consists of the mouth, esophagus, and stomach. It is here where most of digestion occurs. In meal eaters (predators), stomachs act as reservoirs for holding and digesting larger, less-frequent meals. In grazers, the reservoirs are smaller or absent and the length of the gut increases as food continuously moves downstream.
Interestingly, many fish have blind pouches where they cultivate their digestive partners and bacteria, and secrete digestive enzymes. In the digestive tract, bacteria not only aid and assist in digestion but also manufacture some of the water-soluble vitamins necessary for health. Their importance cannot be stressed enough. Friendly bacteria provide a crucial service in exchange for habitat and food, and digest most of the complex carbohydrates in the gut. The process involves chopping two carbons off at a time. When you use an antibiotic to treat an infection, you are attacking not only the pathogen, but also the beneficial flora in the gastrointestinal tract, a delicate mix of a variety of aerobic and anaerobic bacteria. I think we all have experienced the GI side effects of a course of antibiotics. You should expect the same in your tank. Prevention through healthy nutrition is the key. Healthy individuals can mount a defense against most invaders, unhealthy individuals rarely do.

Feed a varied, all natural diet. There are some excellent all-natural frozen varied and single-source products on the market. Feeding a single-source product only might seem to be palatable but it is akin to you or I eating chocolate cake for every meal. Soon, we would tire on it and likely become malnourished, as no single product can or does provide a complete nutritional profile. Certainly, there are exceptions to the rule, but the vast majority of animals need a varied diet to be healthy. Unique single-source foods should be part of a varied, all-natural diet. Food quality is also important as the more digestible, the higher the quality. Nature does not add supplements to enhance quality, or binders as stabilizers, but high-quality foods packaged in recognizable forms that provide complete nutrition.

Make fish eggs/roe part of your feeding routine because they are the “gummy bear vitamins” for your reef inhabitants. They are packed with essential vitamins, minerals, essential fatty acids, and essential amino acids. They are a recognizable food for all marine inhabitants, and should be considered an all-natural alternative to expensive supplements.


Wanted dead or alive: phytoplankton and/or spirulina.  Phytoplankton is the source of essential fatty acids, essential amino acids, and many vitamins; all are critical for optimal health. It is food for zooplankton, corals, and all other filter feeders. Dead phytoplankton is food, but becomes detritus if not consumed. Live phytoplankton is food and a consumer of phosphates and nitrates, converting CO2 to O2. Whether the amount added to any individual closed ecosystem is significant is unknown, but is definitely safer than dosing or overdosing with dead or dying algae from concentrating or centrifuging. If you are unsure about a product, take a look at it under a low-power microscope; if you see chaining or clumping, it is likely dead or dying. Finally, feeding single-source marine algae may not meet all of your tank’s inhabitants’ nutritional needs. Essential fatty acid content varies widely amongst different species with the two principle Omega-3 fatty acids, EPA and DHA, having very different roles in health. See figure #3 below for details.The highest DHA is actually found in golden brown algae.

ColorMotilityEssential Fatty Acids
NannochloropsisGreenNon Motile, no FlagellaEPA
TetraselmusYellow Green4 Flagella moves rapidlyEPA
IsochrysisGolden Brown2 Flagella, moves and rotatesDHA AND EPA
PlatymonasLime Green4 Flagella motile and non motile life stagesDHA AND EPA
D.SalinaOrange Green2 Flagella, moves rapidly and shakesEPA

Figure #3

Spirulina is an interesting organism, and like other single-cell algae, it is a source of essential fatty acids and amino acids. Some consider it to be cyanobacteria, others a marine alga. Spirulina is all-natural and healthy.

Add copepods/zooplankton as both food and detrivores – because they are! Similar to our own food pyramid, in a healthy ecosystem, there is a detritus pyramid to process waste, and live zooplankton are a critical mid-portion of that pyramid. In addition, they consume marine algae, breaking it down and making a simpler form, which is then available to many of the benthic and pelagic feeders in your tank. There are both pelagic and benthic forms, and both are important. Some are detrivores and others are herbivores. Harpacticoids have short antenna and Calanoid have long antenna; Zooplanktons are what they eat. Commonly available in the market are Tigros (benthic detrivores), Parvo (pelagic herbivores), Tisbe (benthic detrivores), Pseudo (pelagic herbivores), and Acartia (pelagic detrivores). A healthy mix is critical to meet the feeding demands of your tank, and adding a variety of pods to your tank will ensure that some (if not all) will establish communities.  During their life cycle, which starts as naupalii, they molt many times and some of the debris on the bottom of the bottle is molts not dead pods.

Like every other animal, zooplankton need a source of food; a clear bottle without nutrients (marine algae) is a starvation chamber. Cooling will reduce metabolic needs but will not eliminate them. Some are cold-water breed, others thrive in the warm water of our aquariums.  Smaller members tend to reach sexual maturity earlier and produce multiple egg cases during their short existence, but they also have a greater chance of passing through your filtration system.The goal should be a vibrant colony of multiple species of zooplankton inhabiting your tank for successful waste management and as gut-loaded food for both benthic and pelagic feeders. The best time to add zooplankton is after dark so they can find hiding places and begin their life cycle.

  Corals, Fish, Invertebrates, Tanks

 John D Hirsch MD

  (3 articles)

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