What’s the poop on fish selection for the Farm in a Box™ with glass tanks? For aesthetics, goldfish and tropical aquarium are popular in small systems. One may argue against goldfish and tropicals as they are not indigenous to our water systems and if by chance they end up in a lake or stream then they become competitive to local aquacultures.
Local Fish: Aquaponics is important as a means of supporting local food production. Any type of fish may be raised in an aquaponic system. But those that thrive in local conditions are ultimately best for promoting local aquatic culture, as they create value within the region. Another option is to catch local stream or lake fish (perch, crappy, bream, bass, catfish, minnows, gamboozia). For education, local derived, cost and purposes of protecting local water colonies, these may be best suited.
Tilapia: Tilapia are about the most popular fish raised and eaten in the US. They are a white meat with a good taste. They produce a lot of ammonia which makes them a good nitrogen source. They also have strong immune systems, rarely getting sick and they tolerate imperfect water conditions, which makes them easy to raise for newbies. However tilapia are tropical and do not tolerate temperatures below 55 degrees. In fact, they like it a very warm 80-90 degrees and grow fastest under these conditions when fed frequently. This means that outdoors, if the weather is not tropical where you are raising fish, then they will grow slower or else their water will have to be heated.
Crayfish: Another ideal source of nitrogen is crayfish. The red tip Australian crayfish also produces a lot of phosphorus, a nutrient important in heavy flowering and fruiting plants. Crayfish are fun to raise and do well in water as shallow as 4″ up to 18″. They are prolific reproducers and are an edible source of protein. Bream, crappy, bass and catfish are other obvious choices. These fish are somewhat more difficult to raise and not as tolerant to sudden changes in pH, temperature and oxygen levels. They grow more slowly than tilapia but are very popular in the american diet. These fish also require warm water to eat regularly and grow quickly and produce a good amount of ammonia. Salmon and other trout prefer colder water year round, though not too cold, and are not commonly produced in aquaponic system thus far.
Nutritional values: In larger Farm in a Box models appropriate fish choice includes those that are edible and provide good nutritional value. Omega 3:Omega 6 ratios and quality of fats are very important. On that standard, the most desirable fish are the Australian Silver Perch and Jade Perch; these have 10x (10:1) better ratio than does salmon (1:1) and a 100x (1:10) better ratio than tilapia. The problem is that these fish are not sold live in the US at this time. Salmon and trout are desirable but are too difficult to raise in captivity for non experts.
How many fish: The San Antonio, Dallas and Phoenix systems will support as many as 25 to 100 edible fish at a time. These fish will not all grow at the same rate, so harvesting for consumption is possible and may be done on successive weeks once they begin to reach maturity. Fish may be sorted by their size by using two or more 100-200 gallon tanks.
Where to get fish: Smaller fish may be sourced at local aquarium shops. Larger edible varieties may be netted out of creaks and ponds. For tropical and larger volumes of edible fish, including tilapia, Earth Solutions can help source them, or else depending upon the laws of your state or municipality, fish may be ordered from hatcheries and delivered by Fed Ex to your door. Quantities of 150 to 500 generally cost $0.50 to $1.00 per fish. For quantities under 150, you may expect to pay $2-3 each.
What to feed fish: Food for smaller aquarium fish can be purchased at the fish store. For larger tilapia a good quality salmon dog food is recommended. Purina makes a catfish food that is commonly used in fish farms and for tilapia. The quality of dog food is superior, though we encourage non-corn feeds, as most corn is genetically modified. Otherwise, raising worms (vermiculture) or soldier fly larvae from composting organic greens will guarantee that not only are your aquaponic vegetables organic but so are your fish. Considering the dire condition of our worldwide water supplies, organic fish is practically impossible to source and growing your own will be the most reliable source. Duckweed is a floating aquatic plant that is easily raised in pools of water for the purpose of feeding fish. Tilapia will eat as much as 25% of their diet in the form of this green protein rich food.
How often to feed fish: Goldfish do well to eat once every other day. Tilapia are heavy feeders and will eat as much as 3-4 times per day when water temperatures are in the 80’s-90’s. At this feeding rate, ammonia and fertilizer production is at its best. In colder weather, much lower feeding is the rule. The best way to determine how much to feed tilapia is to feed ad libidium. In other words, feed until they stop eating. For 20 or so tilapia that are between ½ and 1 lb, you may expect them to eat about 2-4 tablespoons of feed every 3-4 hours.
My fish are dying; What can I do? Often this is caused by either not acclimating the fish to the new environment. They should be added by setting the bag into the water so the temperature adjusts slowly. Then let in some tank water into the bag and repeat this every ten minutes or so up to about 30-45 minutes. If they are dying after having been in the tank for a day or so it may be because the rocks were not thoroughly rinsed. You may want to do a 50% water exchange. Be sure to use non-chlorinated water. If you are feeding the fish too much food, they may die as ammonia will be produced too abruptly. If there is no bacteria in the rocks because they did not have a chance to colonize then the ammonia will not be removed and fish will die from their own waste. Bacteria will colonize only under balanced conditions. They need aeration through the ebb and flow cycle and it takes up to a week with exposure to ammonia for them to colonize.