The Aquaculture Component to Aquaponics
While many of you are familiar with the concept of aquaponics, as well as several basic components of aquaculture and hydroponics, there is some other information you need before you give freshwater aquaponics a try.
In 2009, total world aquaculture production of fish was still significantly lower behind wild caught production (55.1 and 90 millions tons, respectively). However, aquaculture remains the fastest growing sector in agriculture, with an annual average increase of 6.6% from 1970 to 2008.
The potential for profitable food production of fish and plants has never been more prominent. After all, aquaculture must supply a growing population and there is an open, global market to generate revenue. Also, there is need for growth and development of additional aquaculture and aquaponic facilities to meet domestic needs.
So, growing fish through aquaponics sounds pretty good, doesn’t it? Well, let me break it to you quickly: not all fish are the same and not all are as easily cultured. So, even though you don’t need to have an advanced degree in aquaculture or prior experience, I still recommend starting simple.
A first point to ponder is if your fish species of interest takes pelleted food easily. If not, you will have great plant production, but no fish to sell and lots of wasted feed.
Personal experience has shown that yellow perch and striped bass and their hybrids are prone to stress and subsequent disease outbreaks.
Freshwater prawns are certainly catching steam domestically, but they are best left to pond production as cannibalism is quite high! While popular, salmonids (trout and salmon) require pristine-water-quality parameters.
For example, they need above 8 ppm of dissolved oxygen, which is only accomplished with colder water temperatures and/or injection of pure oxygen—an endeavor that is pricey and potentially dangerous to your aquatic friends.
Therefore, it is recommended to try black/white crappie (Pomoxis nigromaculatus and Pomoxis annularis), bluegill and relatives (Lepomis spp.), largemouth bass (Micropterus salmoniodes) and tilapia (Oreochromis spp.). In regards to fast growth, high-stress threshold and ease of accessibility, tilapia is arguably the best choice.
Fish meal comprises the bulk of protein in most fish diets. Origins of this feedstuff are predominately harvested from marine fish like menhaden.
The harvest of these fishes domestically has been capped, thus creating an exponential growth in price. Therefore, for aquaculture to be sustainable, fish meal cannot comprise the largest component of diets.
Instead, alternative plant-based protein sources have been tested and utilized.
Due to domestic supplies, soybean meal is one of the better sources of protein suitable in aquatic diets, but is not without problems (refer to anti-nutritional factors in soybeans for more information).
Tilapia is considered an omnivore and is very tolerant to a high inclusion rate of soybean meal in pelleted diets.
Though proteins, carbohydrates and lipids are integral to fish production, it is the mineral premix found in fish diets that is most important to plants.
This mineral premix will contain most of the macro- and micronutrients needed for plant growth and development.
However, be aware that fish will utilize a large component of the nutritional value of the pellets; as such, overfeeding will be integral for aquaponic systems to ensure there are no plant-nutrient deficiencies.
Proper water-quality parameters are also paramount to fish and plant health. Ammonia is a waste product that is excreted via the gills, urine and feces of fish.
However, ammonia at a specific dose is detrimental to fish and plants. To forgo frequent and inefficient water changes, be sure to promote denitrifying and beneficial bacteria. Nitrosomonas spp. and Nitrobacter spp. in turn will convert ammonia to nitrite and then to nitrate. It is this final form that is relatively non-toxic to fish and that can be directly utilized by plant roots.
For “seeding” the water, you can add fish waste via a low-density stocking of fish. Or, for fishless seeding, target a dosing rate of at least 1 ppm ammonia directly.
This will promote colonization by Nitrosomonas spp. bacteria. As the ammonia levels drop and nitrites increase, subsequent Nitrobacter spp. bacteria colonization will occur.
A critical component to keeping both types of bacteria healthy is having sufficient access to their food sources at all times. Therefore, if you are doing a fishless seeding, make sure you do not allow ammonia levels to reach zero, as this will eventually lead to a crash in the Nitrosomonas spp. Population, negating the whole process.
Also, do not add fish to pre-seeded water if the levels of ammonia are 1 ppm or above.
Both fish and plant roots alike are net consumers of dissolved oxygen. If values are too low, both will suffer from stunted growth or death.
A give-and-take relationship exists between the ideal water temperature for fish production and the concentration of dissolved oxygen that will impact plant health.
Given the constraints of temperature, dissolved oxygen should not fall below 5 ppm.
Additional air pumps might be necessary for the fish effluent entering the hydroponic system. Another big water quality parameter is pH. Ideally, pH should be 6.5 to 7.5.
At this range, macro- and micronutrients should not be tied up and the fish will not be bothered. It is important to note that while the above mentioned parameters are critical to both fish and plants, there are other tests—such as for calcium, phosphorous, potassium, iron, etc.—that might be important in monitoring the “nutrient” solution of the fish-culture water.
Be sure to use available resources in the form of university extension publications and various textbooks on aquaculture and aquaponics for specific details. It’s worth it, as aquaponics truly offers an efficient means of sustainably growing food sources for an ever-growing human population.