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Marine Nutrition

Probably the most overlooked component of proper fish keeping. 

By Aaron Lobada


The purpose of this article is to reinforce the fact that keeping healthy, growing and happy fish requires proper feeding. Because corals and anemones have unique feeding requirements that deserve their own article and because my experience with invertebrates is limited, this article will focus on meeting the nutritional needs of fish. So let's get on with it!

Although some high quality flake foods have been developed, they still lose nutritional value and flavor soon after entering the water.

What to feed one’s fish is easily one of the most overlooked components of proper fish husbandry. We all grew up contently putting flake food into our gold fish bowls, only to doom Goldy to die from poor water quality or malnutrition. This is one of the many habits that establishes young and stays with us, even when it comes to keeping expensive marine livestock. It is very easy to believe that fish can thrive on brine shrimp (widely regarded as the marine equivalent of gold fish flakes), and unfortunately it is an all too common misconception that many others and I fell into believing when we first joined the hobby. There is nothing really wrong with feeding brine shrimp, as long as it is not the only food being offered and is only a small part of your fishes diet. I mean, c’mon, how would you like to eat tuna fish sandwiches every day for the rest of your life, when you could be indulging in delicious mysis shrimp or delectable squid?  The benefits of a nutritious, varied diet are too great to neglect and the consequences of poor nutrition can have serious repercussions.  

Why Bother? 

There are a few very good reasons for investing in good nutrition for your fish. The most important reasons for a nutritious diet is to keep your fish happy and healthy. As Conscientious aquarist you take on the responsibility of giving the best care for your fish. They should be thought of as family, not just object that can be replaced if it dies. With reefs and fish populations dwindling because of human activity, it is important to take the best care of livestock, for the benefit your own benefit as well as the environment as a whole. Proper nutrition is a huge part of good husbandry.   

There are also personal rewards to be gained from good feeding habits. It is a good feeling to know that you are taking good care of your pets!. Also, nothing can replace the satisfaction of seeing your fish grow in size. To raise a fish from one inch to several is a great accomplishment and cannot happen without proper feeding. Just like people need calcium to grow strong bones or protein to grow muscles, fish need high quality food to be able to thrive and grow as well. Also, breeding requires impeccable health and energy to spare, so any plans to breed fish must begin with proper nutrition.

Most people will take note of the importance of nutrition in disease prevention. Fish that are fed a healthy diet are more resistant to disease. Spending the few extra dollars on proper food will help save money in the long run. Fish suffering from malnutrition may get diseases that a healthy one might not get at all. Diseases can cost tens if not hundreds of dollars to treat, they cause a lot of undue stress, and they waste a lot of time. Tank teardowns, loss of expensive livestock, constant water changes, medication, and weeks to months of time are all problems that could occur. Save your self these hassles and the guilt of being cheap! Feed ’em the good stuff.  

What Do I Feed My Fish? 

This local fish store freezer contains a wide variety of foods, many of which are formulated to meet the needs of specific groups of fish.  Photo by Adam Cesnales

A common question is "what am I supposed to feed my fish  It is impossible to give one overall answer because different species of fish have different diets according to their habitat and their body structure. Lionfish are slow moving carnivorous predators and gulp their food whole. Triggers, with there sharp teeth are built more for tearing and ripping their prey to shreds. Herbivores such as tangs and some blennies, have mouth parts adapted for picking or scraping algae from rocks. As you can see different fish need different foods. It is always wise to research the needs of a fish BEFORE PURCHASING IT. This includes knowing what their natural diet and feeding behavior is so that it can be duplicated. Commercially prepared foods are available to meet the needs of herbivores and meaty foods are available for carnivores.  To illustrate the importance of behavior, Lions and triggers might only need one large feeding everyday two or three days, while more active plankinovores (Chromis, Wrasses, Anthias) could be fed small amounts several times a day.  Mother knows best so might as well listen to mother nature on this one.

For fish that enjoy more meaty food there are plenty of different foods out there. Squid, mysis shrimp, krill, clams, mussels, and crab all make excellent food for most fish that eat meatier foods. Brine shrimp should be avoided because of its poor nutritional value, but it can be used as a treat.  Even live brine shrimp is a poor choice for frequent use, but can be used to try to get new additions or finicky eaters to eat. When it comes to meaty foods, frozen is best as it retains most all of the nutrients in the food. Freeze dried foods are less desirable because they retain less nutrition. Fish with such as triggers and puffers that have teeth designed for cracking shells should be provided food with a shell or hard outside. Crabs legs with the shell and unpeeled shrimp not only provide the stimulation of natural feeding behaviors, but they also help prevent the dangerous overgrowth of these fishes teeth.

Dry food offerings include freeze dried crustacea, flakes, pellets and soft "plugs" and are available in a variety of formulations.  Thoughtful manufacturers include nutrition information and expiration dates.   Such a wide selection can be confusing, so when in doubt, read the ingredients!   Photo by Adam Cesnales

For fish that eat more plant-based material there are plenty of seaweed and plant based foods that can be purchased. Some fish will also eat algae growing on rocks and equipment in your tank and a culture of hair algae can even be kept for herbivores. Some human foods can be used such as lettuce and cucumber but should not be the only part of the fishes diet. Not much preparation is needed but I would wash of the vegetables in water before putting them in the tank. I have heard of fruit being used to feed fish but I would search it to see if it appropriate for your livestock. As mentioned before, foods of marine origin are better if they are available.  Dried seaweed products are available from fish stores, and asian grocery stores often stock a variety of nori, kombu and other dried algae products (be sure they haven't been seasoned!) There are many different handy clips you can buy specifically for holding these kinds of foods in fish tanks and should not cost more than a couple of dollars. Some are even in fun shapes like clownfish and turtles.  From a behavior point of view, trapping the food in these clips provides a grazing like feeding activity for herbivores.

Extra attention must be paid to slow, finicky eaters (frozen mysis are often the only prepared foods that are accepted by Bangaii Cardinals like the one pictured).

Now that we have covered how to best meet the needs of the fish, let's look at  how to choose foods that meet those needs..  Frozen foods do tend to retain more nutritional value and have more natural textures but they contain a lot of moisture.  This  higher moisture content makes frozen foods more expensive for the amount of actual nutritional value.  Dry foods do not contain as much moisture so they have more food value per unit of weight and are generally more economical.  Flake versus pellet is another area of contemplation.  Flakes are usually readily accepted by fish and quickly gobbled up but because they are so thin, they can lose nutrition to the water quickly. Pellets may not be as enticing but since tank water cannot penetrate them as fast, they lock in nutrients better.  No matter which form of food you choose, another good habit to get into is reading the ingredients on the packaging.  For marine fish ingredients of marine origin are almost always superior to those of freshwater or terrestrial (Land) origin.  The types and amounts of nutrients in marine based food is unique and is what your fish are normally exposed to in their natural habitat.  This is important for herbivores because marine algae are easier digested and higher in some nutrients than terrestrial greens such as lettuce, spinach, cucumbers, peas, etc.  It is also important for carnivores since the types of fats in marine meats is very different from those from land or freshwater. Last but not least....  VARIETY, VARIETY, VARIETY!!!  It cannot be stressed enough how good variety is for your fish.  Even the most nutritious foods do not contain everything your fish needs and you do not want your fish to become bored with their food.  Vary it between dry, frozen, flake, pellet, and even different brands because all brands don’t have the same amount/kinds of nutrients/ingredients.  Think of it as a food pyramid for your fish.


Selcon is a preparation that includes important marine fatty acids as well as vitamins. It is a beneficial supplement for all fish and is a necessity for rearing young marine fish like clowns.

Most foods can be augmented with specifically designed marine supplements. Selcon is probably one of the best and most expensive and is what I use in my tank, inducing a great feeding response from my fish. It contains Fatty Acids, Lipids, Vitamin C, and B-12. It also leaves traces in the tank for filter feeders. Many aquarists have reported good results using multi vitamin preparations like vita-chem.  Just like human nutritional supplements, care should be taken not to overdose such additives. Garlic is also used and can be purchased as a marine aquarium supplement from most online retailers. Garlic helps to induce a good feeding response and is some aquarists believe that it boosts their fish’s immune system.  For large predatory fish that eat larger pieces of food,  supplements can be directly injected into the piece of meat.  In the wild, predators benefit from the nutritional value of whatever highly nutritious food was recently eaten by their prey. This can be replicated by making a pocket  in a piece of meaty food (or using the belly cavity of silversides) and stuffing it with nori, dry fish food, frozen cube foods to add nutritional variety.  Think of it like getting children to eat their veggies by smothering them in cheese sauce!

Storage and Handling

Proper storage and handling of fish food is often neglected.  Even the most nutritious foods will lose value if abused.  Fish food just like human food is best if kept in the refrigerator.   It is best if food is kept in a cool dry place away from intense light, so obviously on top of your tank hood is not a good place!   Even dry foods that don't require refrigeration will retain more nutritional value longer in the refrigerator.  Make sure frozen food is, believe it or not, stored in a freezer!  Be sure it is stored tightly to avoid freezer burn -  Ziploc bags work well for this. A good rule of thumb is to get rid of food about 6 months after you open it to be sure that your fish are getting fresh food.  If your food is past its expiration date (If it has one), it is obviously a good idea to throw it out and pick up some more.  That is about it for storage.  Basically be sensible.  Think of how you would store your food and that is probably how you should store your fishes’.

A Few Pointers

  • Beware of overfeeding… it can be just as detrimental as underfeeding because excess food will decompose and compromise water quality very quickly. Feed little bits at a time allowing your fish to consume it all before adding more. Stop adding food if the fish start to lose interest.

  • For very small fish, food may need to be minced into smaller pieces to reduce the chance of your fish choking. (Yes fish can choke and I have heard of it happening).

  • Some slower moving fish may not be able to compete with faster fish that get to the food quicker. In such cases feed the other fish first away from the slower fish and then while they are occupied feed the slower one. For liquid/frozen foods you can use a cheap plastic syringe to directly feed the slower fish. Although the fish may be shy at first, after a couple uses it should be okay once it realizes food is coming out of it and the syringe is not a threat.

  • For dangerous fish such as lions, eels and triggers a feeding rod may be used to reduce the chance of injury. Aside from the risk of being bitten, lionfish spines are venomous and will cause very painful injury that has been compared to a bee sting but much worse.

  • Do not allow frozen food to thaw only to be frozen again.  This can cause huge loss to nutritional value.  Make sure you purchase frozen foods right before you go home to minimize any thawing that may occur.  It might even be wise to bring something to insulate the food in once you purchase it.  Inspect frozen food packages for excessive ice crystals that either indicate that the food is old or was allowed to thaw.

  • Check for expiration dates on the packaging.  One it lets you know how fresh the food is/ how close it is to expiring and it is a sign that the manufacturer cares about the quality of their food.  Take note that most foods don’t have these but it never hurts to look.

  • Lastly, have fun and enjoy watching your fish eat!!!!! It is one of the best parts of the hobby to see your fish go nuts over feeding time. Also, it is a good chance to observe fish for injuries or infections, especially ones that stay hidden most of the time.

There you have it. A quick spiel about why nutrition is one of the most important but unfortunately overlooked aspects of caring for fish. Hopefully this article will help aquarists make better more appropriate food choices for their fish.

Marine Foods/Feeding/Nutrition on WWM

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