In an aquaponics system the fish feed is the main input.  The quality of feed you select not only determines the health of your fish, but also considerably affects the health of your plants.  The old adage “GIGO” or “Garbage In Garbage Out” definitely applies to the role of fish feed in aquaponics!

In this article I will take you through how often to feed your fish, using auto-feeders, selecting the commercially produced feeds while accounting for feed composition, and some options for supplementing with home grown feed sources.

When and how often?

Fish tolerate a wide range of feeding schedules very well.  They actually adjust their metabolism to match food availability.  If you want your fish to grow quickly, or you have fewer than the recommended fish and need to produce more food for your plants, go ahead and feed them often.  Commercial aquaculture operations feed their fish as often as once an hour.  If, however, you are in an overstocked situation, or had an insect outbreak in one of your planting beds so you need to replant but only have small seedlings available, or for any number of other reasons, you need to “dial down” the amount of fertilizer your fish are producing, simply feed them less.  I often only feed my fish once a day, in the morning when I go to check on everything.  Sometimes, however, I’ll feed them again in the evening if I need to go to the greenhouse to pick some produce for dinner.

The best fish feeding rule of thumb is only feed your fish as much as they will eat within five minutes.  After five minutes, remove the remaining food from the tank with a fish net.  Soon, you will be able to judge just how much food to toss in, depending on your fish’s behavior at that moment, and you will no longer need to wait five minutes to see how much they eat.

The time you spend observing your fish when you feed them is very valuable.  Thus, you should avoid automatic feeders unless you are going on a short vacation and have no one to take care of your fish.  Automatic feeders aren’t inherently bad, but if your fish stop eating, something has likely gone wrong with your system and you will not receive this critical signal if you aren’t there at feeding time.  Fish may stop eating for a wide variety of reasons including water temperature being outside of “thriving” range, pH being outside tolerable range, too much ammonia and/or nitrites (a fish may have died in the tank giving off excess ammonia), too little oxygen, stress or a disease.  All of these are easily corrected if caught early, and potentially fatal if not.

Commercial feed

Tilapia Pellet

Commercially prepared fish feed is an excellent source of nutrition for your fish.  There are typically two types of fish feed sold in the U.S. – omnivorous and carnivorous – and they vary mostly in their protein content.  Within these types, you can select feed according to the stage of growth your fish are in.  Again, the formulation difference will largely be the amount of protein in the feed, although you will also notice a difference in pellet size.  Not surprisingly, as the fish get older, the size of the feed pellets gets larger.

Fish feed is comprised of proteins, fats, minerals, carbohydrates, and other nutrients that a fish in the wild would have in their normal diet, but that they cannot get in what is essentially a wet desert in captivity.   The sources for these nutrients are usually from fish meal, corn, soy, and other animal bi-products.

While we might find some of the ingredients in commercially available fish feed distasteful, one fish feed producer once described them to me as follows:

“For healthy fish, and in turn healthy food for people, these missing nutrients must be supplemented. Poultry meal provides about 65% protein and 6% calcium by weight. It also supplies about 4% phosphorus by weight and 19 important amino acids that tilapia and most other fish require for proper growth and reproductive functions. Poultry meal is poultry bone and meat that is cooked at extremely high temperatures before being added to the food mix. It is basically the equivalent of a ground chicken patty. Dried animal blood cells are just another way of saying hemoglobin. It is a highly nutritious, non-bovine ingredient that provides iron, phosphorus and many micronutrients that aid in oxygen absorption and gill health for the fish. Porcine Animal Fat is simply cooking lard (what makes pastries so “puffy” and flaky). It serves as a binder, a source of important fatty acids and aids in digestion.

Without these nutrients, the fish would have higher “bad” omega fatty acids and lower “good” omega fatty acids. A diet consisting primarily of soy, corn, rice and/or wheat will produce a fish that has significantly diminished health benefits for human consumption. This is actually a big reason why the nutritional value of store bought tilapia from overseas has been questioned so much recently by the media. Properly fed tilapias are a very healthy protein source.”

Kellen Weissenbach
Premium Fish Food

The protein in fish feed comes mainly from fish meal.  Fish meal can come from fishery wastes associated with the processing of fish for human consumption or from specific fish (herring, menhaden and pollack) which are harvested solely for the purpose of producing fish meal.

There is currently intense debate within the aquaponic and aquaculture communities about the wisdom of adding to the serious problem of over-fishing our oceans by feeding our farm-raised fish – fish from the ocean.  Thankfully, many experts are conducting ground breaking research to develop protein substitutes for fish meal.  An article in the Aquaponics Journal (issue #56, Q1 2010) highlighted three companies creating protein sources. At Ohio State University, aquaculturalists are exploring the feasibility of using soybeans to replace fish meal and plan to soon test the product on yellow perch. Scientists at the Agricultural Research Services and Montana Microbial Products have teamed up to produce a barley protein concentrate that can be fed to trout, salmon and other commercially produced fish. Finally, in Idaho Springs, Colorado, Oberon FMR has signed a deal with Miller-Coors to use 5,000 tons of beer sludge in combination with other ingredients to produce 6,000 tons of fish food flakes.

All fish feed, especially brands that use more natural ingredients and fewer preservatives, have a limited shelf life and are best stored in a cool, dry location.

Home grown feed

Duckweed Pool (image credit: David Hart)

Supplementing, or even entirely substituting your own, home-grown fish food can be personally satisfying, save money, and further decrease the environmental footprint of your aquaponics system by further closing the input loop.  The following is a list of some of the feed that can be easily cultivated for most omnivorous fish:

Duckweed –This fast growing aquatic plant doubles in mass every day when in its ideal environment.  In addition, duckweed is over 40% protein (more than soybeans) and efficiently removes contaminants from and adds oxygen to the water.  Duckweed grows best in dappled sunlight in relatively stagnant water with some fish waste.  The key is to keep it in a separate tank from your fish or they will just eat it all!

Worms - Earthworms, sludge worms, bloodworms, and composting red worms (AKA red wrigglers) all make excellent fish food.  The challenge is to grow enough of them to be more than an occasional, although probably very appreciated, treat for your fish.

Black Soldier Fly (BSF) Larvae – The Black Soldier Fly is considered a native of North America, and can be found in many parts of the United States. It is exceptionally active in the southeastern U.S. from April to November. Their grubs are considered beneficial scavengers in nature, and help to digest and recycle decomposing organic material including carrion, manure, fruits, and decaying plant waste. Their association to humanity is limited to compost piles, facilities producing manure, and poorly serviced toilets. Unlike the common house and fruit flies, they are not commonly found in association with humanity (picnics, kitchens, residential buildings, etc.).  While the mature fly has a short lifespan of only 5 – 8 days, the female can lay over 900 eggs.  Those eggs hatch in about 100 hours and, if conditions are right, will mature in 2 – 4 weeks.  During this stage, the larvae make excellent fish food, as well as robust compost consumers.  A product called the BioPod is specifically designed for BSF food composting and through clever design, has the added benefit of self-harvesting the larvae.

Other kitchen and garden scraps – Omnivorous fish like most bland-tasting, non-flowering plants and even some fruit.  I’ve found that my tilapia especially appreciate lettuce that is getting slimy and no longer fit for human consumption.  I’ve been told that they will eat untreated grass clippings (no weed killer or pesticides!).  They get very excited about the uneaten tops of strawberries.  Experiment!  If they don’t eat what you have given them in five minutes, and it is their normal feeding time, remove it from the tank and chalk it up to experience.  What have you got to lose?

I recommend that you consider any one, or a combination, of the feeds above as a supplement to a commercial fish feed.  Nutrition for living beings is a complex subject, especially in captivity. Just as we wouldn’t feed our dogs or cats exclusively a single, or even a couple foodstuffs, please consider feeding your aquaponic fish a varied diet that includes a reputable commercial feed.  Consider it a vitamin tablet for your fish to ensure that both they, and ultimately your plants, are getting all the nutrients they need.

Next months’ Aquaponics Explained article will be about Hydroponics vs. Aquaponics, and how they differ.

Words: Sylvia Bernstein, www.theaquaponicsource.com