I always enjoy the innovation that I see with the Mother Earth Fair community and I wanted to approach this second part of the cage culture discussion from the standpoint of innovation. I think that there is room to incorporate sustainability through innovation in rearing fish in cages.
Coosa Catfish Cages was a small business in Coosa County, Alabama, that Shep Phillips operated. He was my friend and great asset to his community. We worked on projects and trade shows together during my beginning adventures in pond management in 1994. Shep was involved with the local water district, as well as Auburn University extension system, and wanted to develop a way for landowners to profit by growing fish in their small ponds. With its rolling hills and plenty of rainfall most years, central Alabama has a lot of ponds in dammed-up ravines. While these ponds supply water for wildlife, irrigation, and livestock, Shep had something more entrepreneurial in mind.
He developed an ideal cage to raise a crop of fish in these ponds, taking materials, mesh size, predator protection, and ease of handling into consideration. He kept a rectangle of 3-inch PVC pipe frame suspended from pine trees in the front yard, where he assembled cages. When his young grandson got too rowdy, he found himself placed inside the suspended finished fish cage as a giant “playpen” 4 feet deep, 4 feet wide, and 8 feet long. The nylon mesh was a sturdy black 1-inch diamond, and capable of holding a good crop of fish (or a grandson). After the unit was assembled, he removed the PVC and was able to ship or deliver the collapsed cage; it could be reassembled with locally purchased PVC for the frames.
To increase production, farmers needed aeration, since the high density of fish would limit the system’s oxygen. The main culture species was channel catfish, which become stressed if you drop an airstone, gushing air bubbles, right in the middle of the cage. An airlift uses air injected into a vertical pipe, aerating the water and creating flow at the same time. After digging through the plastic file box in the back seat of my truck, I found a scientific article I had recently read on airlifts. We looked it over and I left it with Shep. By my next visit, he had adapted the concept to attach to the side of his cages; the design would push fresh aerated water across the cage lengthwise without stressing the fish. This may not sound significant to you, but to his farming community, it effectively aerated the cages, which meant the ability to culture 20 percent more fish with the same effort.
Now, innovation is a funny thing. It includes success, failure, and lackluster results. I hope that you will take a standard, even conservative, approach initially to create success for you and your fish culture project. Some sustainable techniques for cage culture are old ideas and some are new. Cage culture is an old activity and has been used around the world and in developing countries. Some of these systems are more innovative than modern approaches, and are a source of knowledge for integrated, sustainable techniques.
Cage culture species are somewhat limited in the United States. Tilapia is regulated by individual states, so you need to check regulations with your state department of wildlife and fisheries to see if they are allowed or if a permit is required. Channel catfish and rainbow trout are also common choices for successful freshwater cage culture in the United States.
Limited research has been done on bluegill, which do not gain weight as efficiently as the previously mentioned species, and commercial marketing may be limited by regulations. Bluegill would likely readily take a natural feed supplement like insects, which could help balance their poor feed conversion of commercial feed.
Carp have limited market demand depending on the species selected. Silver and bighead carp are filter feeders and rapidly gain weight in algae-rich ponds without supplemental feed. These may also be regulated by state agencies. There is a traditional market for carp among communities from Europe, Asia, and the Middle East.
Feeding is one of the major expenses and alternative supplemental feed is one way to reduce that, but don’t forget that it is exactly that — supplemental. Don’t forget that your fish are confined; you are responsible for feeding them a balanced diet to keep them healthy and growing.
Insects, worms, and larvae provide a high protein-supplement. I mentioned in my previous post that the bug-harvesting machines are a tool that could show promise as a way to supplement fish diets with high protein insects which would be readily taken by catfish, trout, and bluegill. Culture of red worms, which would be a likely activity on a sustainable farm, could be used to supplement fish diets. Several methods of larvae culture could supplement fish culture, just as they have more commonly supplemented chickens. Historically silk worm farms have integrated fish culture into the farming activities.
Plant material can provide supplemental feed as well. Composted rice bran has been used as a diet for tilapia. Duckweed is a small, floating aquatic plant that grows rapidly and is high in protein. This has been used to feed tilapia. Be careful as duckweed is small and escapes a cage easily; it can grow rapidly to cover the main area of the pond. Planktonic (single-cell, free-floating) algae is a source of nutrition for filter feeders like silver carp, bighead carp and some species of tilapia. Algae growth can be stimulated with fertilization of the pond. This stimulated growth of phytoplankton is called a “bloom” and needs to be monitored to avoid overproduction which can lead to a sudden die-off, depleting oxygen.
Aeration, as mentioned earlier, can increase production by 20 percent. The airlifts system is an option if you have power at your pond. If you do not have power near your pond, or if you are off the grid, you need other options. High-volume surface aerators used in small and large cage culture operations require 120- or 240-volt power. Diffused aeration injects air to the bottom of the pond and gently mixes large volumes of water, keeping it breathing and exchanging gasses with the atmosphere above. If you don’t have power near the pond, this is still an option since some compressor systems can deliver air more than a mile away. Once at the pond, air is distributed to diffuser stations. Windmill aerators use a direct-drive air pump powered by a windmill to supply compressed air. The problem is that they work inconsistently and don’t store power for a more consistent effect on your pond. A new option available is a 12-volt high-volume surface aerator by Kasco Marine, the company I work for. One recreational pond owner and innovator adapted this aerator to his well-constructed solar system and aerated his pond all summer in 2013. I think that new 12-volt option could be used for cage culture in remote areas as well.
There are many other considerations for cage culture of fish: predators, cage construction, health and disease, marketing. Below are links to supplemental articles on cage culture that can help you complete your plan. I would enjoy hearing about your ongoing or future fish culture projects, so leave me a comment here or email me at firstname.lastname@example.org.
Cage Construction, Placement, and Aeration
Cage Culture: Site Selection and Water Quality
Mother Earth News: Farming fish in Cages (1983)
Next time, I will discuss ways to control overproduction of algae. Warmer weather is on the way and algae always follows.