Fish and Aquaponics

For some, the main appeal of aquaponics is the ability to grow one’s own food. However, others see aquaponics as a way for beautiful and serene fish to be a part of a sustainable ecosystem. Because fish are an essential part of aquaponics systems, it is imperative that special care is given to this area of the set-up process. Let’s start with some frequently asked questions before going into detail.

Should I set this up like my aquarium? 

One of the most common misconceptions about aquaponics is that it is set up like an aquarium, but with plants added. However, the amount of fish must be properly calculated based on the size of your tank and expected size of fish at “harvest.” This is discussed later in more detail.

Most people who have aquariums have them on display in a living area, and therefore keep them very clean. While cleanliness is important in aquaponics, so is the production of needed bacteria. While it may be tempting to keep the tank squeaky clean, bacteria on the sides of the tank are actually beneficial for the system. Diseases are also rarer in aquaponics systems than in aquariums, and many scientists believe this is due to antibiotic properties present in plant roots. In addition to these differences, water temperature and pH balances are often easier to keep stable, as the tanks used are usually larger than residential aquariums.

What types of fish can I include in my aquaponics system?

Freshwater fish are the only types of fish that can thrive in an aquaponics system. Because most plants can’t tolerate high sodium levels, salt water set ups are simply not possible.

The type of fish you place in your tank shouldn’t just be a type you are fond of or find attractive. You’ll want to take several factors into consideration. First, will you be consuming any of the fish from your system once they mature? Next, ensure that the placement of your system allows for the needs of the fish you are considering. For example, fish that thrive in warmer temperatures will thrive in an area with natural indirect sunlight, while those that thrive in cooler temperatures would likely not survive very long in a sun filled area.

In addition to these factors, you also need to consult your local Fish and Game Department to see what types of fish are legal to own in your area. This may seem outlandish to someone just getting started, but there are several reasonable guidelines regarding particular types of fish. For example, tilapia is illegal in some areas such as Florida, because of how quickly it can take over native fish populations if released into the waterways.

Once you’ve decided whether or not you’ll be consuming any fish from your system, established the area your tank will be located, and investigated what you are allowed to have in your area, you’re ready to look at options for fish. Some of the most common fish used in aquaponics are listed below.

  • Koi: These “giant goldfish” are hardy and great for beginners who do not plan to eat any fish from their systems. They grow best at temperatures between 65 and 75 degrees Fahrenheit, are omnivorous, and can grow up to 20 pounds over a period of three years. They have low oxygen needs as well, which we’ll discuss in further detail later.
  • Goldfish: The availability of these fish make them an attractive option. They are easy to find and easy to grow. They can tolerate a wide range of temperatures, and are therefore suitable in almost any system where the fish is not consumed. Their optimal temperature is also between 65 and 75 degrees, and they are omnivorous with low oxygen needs. They take about three years to reach maturity, similar to koi, but they usually only grow to be about four inches long in size.
  • Catfish: These fish not only grow quickly, but they are hardy and easy to care for. In addition, these fish are edible, and are popular in areas where Tilapia is illegal to raise. These fish reach maturity in just 12 to 18 months, and generally weigh around 1.25 pounds at maturity. These fish also have low oxygen requirements, and their optimal temperature is about 75 to 85 degrees, making them ideal for warmer climates. In addition, they are omnivorous.
  • Tilapia: Not only is this fish delicious, but it’s perfect for tanks with a little sunlight exposure. It thrives in waters above 60 Fahrenheit, as it originates from the lake waters of Africa. It also reaches its full “harvest size” in as little as nine months, so it’s quick to grow as well. At maturity, they usually weigh about one pound and a half, and their optimal temperature is 74 to 80 degrees. These fish are omnivorous and have low oxygen needs.
    • Notes about Tilapia and breeding: Tilapia can reproduce very quickly, overwhelming your biofilter as well as your tank. Adults and young alike will consume eggs or young hatchings, but rarely to the degree of population control. Often, a predator fish must be introduced to help with this. Ideally, you should consult with someone familiar with raising tilapia before adding them to your tank. At minimum, insure that your vendor can provide all females until you are ready to try breeding these. It should be noted that while all males should be assumed not to reproduce as well, there are actually two ways that tilapia become male. One is by genetics, but the other is by “direct hormonal sex reversal.” The latter is only about 95% effective, and beginners should take precautions regarding this.

Other popular choices for fish in aquaponics are oscars, trout, perch, shrimp, barramundi, pacu and even freshwater lobsters. To further determine which fish may be best for your system, be sure to factor in the requirements in the next section regarding feeding and more.

How many fish can I host in my system at a time?

For residential systems, the recommendation is generally one pound of fish for every five to ten gallons of water in your fish tank. However, taking this a step further to account for the waste build up can save gardeners a great deal of time in the long run. Put simply, your ecosystem needs ammonia to convert to nitrates. These nitrates create a biofilter, which has to mature. By beginning your tank with the simple rule of one fish per five gallons of water, you allow the fish and the biofilter to mature together, creating a balanced and healthy ecosystem. This is because as fish mature, they release more waste.

Factors for Basic Setup

After reading the FAQ, you probably still need much more information to get started. It can seem overwhelming at first, so let’s take a look at several key factors that will get you headed in the right direction.

Adding Fish to Your System – Wait for the right time.

  1. Be sure that your system has fully cycled. For more information on this and step-by-step directions, Bernstein’s “Aquaponic Gardening,” does a spectacular job of this in chapter 14.
  2. Check your pH levels. When you are preparing to purchase fish (once you’ve chosen the type you prefer using the guidelines we discuss later), ask the vendor about the pH that the fish were raised in. You will want to insure that your tank is matched to this within two-tenths of a degree. Once the fish have been settled, you can slowly adjust the pH to the suitable range for aquaponics (6.8-7.0).
  3. Check your water temperature. Similarly to pH levels, a drastic change in temperature can cause fish to become stressed, sick, or even die. For the best transition, leave the fish inside the bag, but add them to your tank for about 10 to 15 minutes. This allows the temperatures to become the same, so the fish is not shocked.

Fish Food

Some fish are herbivores, while others are omnivores or carnivores. This affects the type of food you will need to regularly provide for them, so they can grow to their maximum “harvest size,” whether or not they are consumed. Your aquaponics garden is, after all, an entire ecosystem, with little interference added other than fish food. This means that each factor is influencing the others, and when your fish grow on track, your plants likely will also.

The metabolism of fish actually changes based on the availability of food, so although a feeding schedule is best, fish are actually quite flexible in this regard. Commercial operations who strive for fast harvest, or growth, will feed their fish as much as 1-7% of their body weight every hour. Generally, once fish reach maturity, they consume about 1% of their body weight in food daily. This should be split into two or three daily feedings. It’s important to understand that more food means more waste produced, so if you notice the waste building up in your tank, you may want to consider feeding them less to help balance the tank again.

As Bernstein states, “The best rule of thumb is to 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 fishnet. Based on your fish’s behavior at that moment, you will soon be able to judge just how much food to toss in, and will no longer need to wait five minutes to see how much they eat.”

Observing the eating behaviors of your fish is a critical way to keep an eye on their health. Automatic feeders take away this important opportunity for assessment, so they should be avoided unless they are truly needed. For example, if your fish suddenly stop eating, there may be an issue with the pH level, but with an automatic feeder, this could go unnoticed. This change in pH, however, could mean a fish in the tank has died, fish are stressed, have too little oxygen or are suffering from a disease.

Before deciding which fish to pair together, or deciding on a type of food to regularly feed them, it’s best to know first if they are carnivorous or omnivorous.

Carnivores

Carnivores consume other animals for their protein source, and therefore require a high protein diet. Fish such as oscars, trout, bass and perch may need a commercial food product specifically formulated for carnivorous fish. Bernstein’s book, “Aquaponic Gardening,” suggests a product by Purina called AquaMax Carnivore. This product is perfect for those who prefer to feed fish just as they normally would in an aquarium, by just tossing in some simple flakes and pellets.

Alternatively, you can opt to provide your carnivorous fish fresh food. Grubs and worms are the best option for those who prefer this option, but care should be taken to ensure that whatever food is provided is sourced responsibly.

One consideration that must be made for carnivorous fish is that some of their behavioral patterns are based on their eating habits. Because these fish consume other fish in the wild, they are more prone to picking at other fish in the tank. This behavior can be minimized by ensuring that all of the fish are around the same size.

Omnivores 

Omnivores are animals that consume both animal and plant based diets. With fish, however, these diet preferences and needs are a major factor in how they behave. Fish such as catfish, tilapia, pacu, goldfish and koi actually coexist better among other omnivorous species than their carnivorous counterparts coexist with other carnivores. This may make for a little less hassle when caring for your tank.

In addition, the eating habits of omnivorous fish are also quite varied, allowing gardeners to grow most of their own feed if they prefer. This can cut costs, while further making your system more self-sustainable. If you prefer the simpler route of simply tossing in pellets, commercial food is also available for omnivorous fish.

Alternatives to Commercial Feed

As mentioned above, growing your own feed is just one small step that makes your ecosystem more sustainable. In addition to growing plants for your fish to consume, there are also other ways you can harvest supplemental feed for your fish. In fact, you can completely eliminate commercial feed with enough “home grown” nutrients, even though most beginners supplement with a small amount of commercial feed to eliminate any doubts about nutrition. Take a look below at some of the alternatives to commercial feed that are available.

Worms: If you’ve ever been fishing, you know most fish love worms. It can be challenging to raise enough of them, but with patience, this is likely going to be a favorite for most fish. They love to indulge in sludge worms, blood worms, earthworms and even red wigglers (composting red worms).

Fly Larvae (Black Soldier Fly): These flies are not commonly associated with people, and are quite different from the fruit fly we have all been annoyed by on hot summer days. They help digest and recycle decomposing organic material such as manure, and decaying fruits and vegetables. Its lifespan is only five to eight days, but one female can lay almost one thousand eggs that hatch within one hundred hours. They then mature in two to four weeks, and it is during this time that they make such excellent fish food.

Duckweed: Duckweed is a common crop for fish feed, because it grows rather quickly and easily. In fact, if grown correctly, it doubles its mass daily. Of course, it efficiently removes contaminants from the water while providing an oxygen source, but it’s also a fantastic source of protein. With a higher concentration of protein than even soybeans, duckweed is about 40% protein. It should be noted, however, that this plant should be kept separate from your fish. Otherwise, you’ll likely find them eating the plant before you are ready to harvest it.

Kitchen scraps: It may seem odd to be feeding your fish kitchen scraps while the family dog looks on, but the truth is that omnivorous fish actually enjoy table scraps just as much as Fido. Nonflowering plants, such as lettuce, and even some fruits are sure to be enjoyed by fish, as well as things like the inedible tops of strawberries. Simply break the food into smaller pieces, and toss it in.

This type of feeding is actually quite fun, as you will get to know what your fish actually prefer to taste. If the food hasn’t been eaten within five minutes (in normal feeding conditions), simply remove it with a net and know that your fish didn’t find it appetizing. You’ll likely notice their excitement over their favorite types of food as well. This can make the experience with your fish much more personal. But beware, you may grow too attached to eat them!

Oxygen Concerns

Many people ask about the different oxygen needs required by specific types of fish. While this is a valid concern, it’s worth noting that you aren’t likely going to provide too much oxygen with adequate water levels. While some fish are native to environments with low water levels and not much oxygen, others are native to large rivers and streams where water and plant growth, as well as oxygen levels, are high. Instead of limiting yourself to certain types of fish based on oxygen needs, just play it safe and instead, keep your tank at levels acceptable for fish like trout, which like high water and oxygen levels. This will allow room for error, as well, in the case of a brief power outage or other unforeseen circumstances.

Temperature Concerns

As you probably already know, fish are cold blooded animals. This means a number of things are very different from warm blooded animals, such as mammals.

  • They do not regulate their own body temperature. While mammals use approximately 80% of their caloric intake on maintaining their body temperature, fish actually use none of theirs.
  • Their cold body temperature means they also do not have any of the warm environments required to breed diseases such as E. coli or salmonella.
  • The temperature of the water is their only influence for body temperature, and therefore must be appropriately monitored and adjusted.

The natural climate of the fish actually determines the need of the water temperature. Other temperatures that are lower or higher may cause your fish to not only be unhappy and stressed, but it can open the door for a plethora of problems, including sick fish.

Many people “test the waters” before deciding which fish are suitable for their setup. For example, a tank that is not placed in direct sunlight or in a drafty area will likely maintain its temperature steadily. This is the most predictable, stress free way to set up your system.

However, you may find that the ideal spot for your tank requires that a heater be used in your tank for the fish’s benefit. With an in tank thermometer and careful monitoring, this is often quite successful. This method also allows you to begin planning for your fish prior to setup, rather than setting up and then planning. However, you will still need to factor in that all fish in the tank will need to have the same optimum temperature for best results.

Alternatively, some who are more comfortable with the careful monitoring involved may choose to place their tank in an area that is warm during certain seasons, but must be heated during other seasons. This can be an ideal solution for those with this flexibility. It’s important to keep in mind, however, as Bernstein states, that it’s much easier to heat a tank than to cool it.

Obtaining Fish in a Responsible Way

As mentioned earlier, it is imperative when stocking edible fish that you consult with your local Fish and Game Department to find out which fish may be illegal in your area. When consulting this authority, you may also want to ask if he or she knows of any reputable local hatcheries. Local hatcheries are an excellent place to purchase fish because they are almost certainly legal in your area, and the fish are likely already acclimated to your climate. As Bernstein mentions, catfish raised in Florida aren’t likely to survive cold weather, but those raised in Ohio will.

In addition to being a good supply source, your local hatchery is also a great place to expand your knowledge. After all, if you have sick fish a week after buying them, there is someone to call for answers.

Sometimes a local hatchery isn’t an option. In this case, you may need to find a reputable vendor on the internet. Keep in mind that shipping will be more costly, as the fish will obviously ship in water. If forced to go this route, you may want to consider asking the vendor to supply you with male and female fish, so that you can begin raising fish, returning to the vendor less often or not at all.

If you aren’t interested in having edible fish in your tank, then a local pet store is sure to have all the goldfish, Oscars, pacus or koi you will need to get started. In addition to pet stores, you may find “Fish Stores” or “Aquarium Shops” or similar in your area. These will likely have a larger selection, and will be a better source for answering specific questions you may have later on in the growing process. Lastly, it’s important to remember that if you are planning to purchase koi, there are many varieties, and they all have vast differences in price. It is recommended to start with more affordable types until you get the hang of everything, particularly the pH levels, so that no large investments are wasted.

It’s Time to Eat!

So, you’ve been eying your beautifully raised, healthy tilapia, and you’re finally brave enough to harvest them for a delicious meal. You may be wondering the best way to go about “fishing” them from your tank, and what precautions are needed. At this phase, some people actually get attached to their fish, and may decide to keep them a little longer for breeding or just enjoyment. Some even release them into the wild when the tank becomes overstocked. Caution should certainly be taken with the latter to insure the fish are in an environment closest to their native breeding. In addition, you may want to consider selling them to a local fish store, so that you can reinvest the resources in your system.

For those seeking to remain true to their original intentions, or their love for fish tacos, harvesting your fish should be as humane as possible. Of course, when harvesting for food, flavor is most certainly important as well. Though not necessary, it is helpful to place the fish into a tank of clean water without feed for a few days. This clean flavor is usually preferable.

Once it’s time to remove the fish for consumption, there are a few methods to consider:

  • Ice water: Likely the best and most humane way to “dispatch” a fish, this method works for almost all fish that do not live in colder climates (for example, trout is an exception here). Put simply, remove the fish from its tank and quickly place it into a bucket of ice water. This action puts the fish into shock so it dies almost immediately.
  • Hitting the fish’s head with a firm object or using a knife to cut the fish between the eyes: While these methods are both quick and therefore more humane than simply letting a fish asphyxiate without water/oxygen, they can also be a bit difficult because fish become quite active once removed from water. Be sure to have everything prepared within a large space, before the fish is removed to make this process easier.

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