Fish farms vary dramatically in appearance depending on whether they’re built on land, floating in coastal waters, or anchored in the open ocean. Some look like rows of rectangular swimming pools, others like clusters of giant floating rings, and a few resemble nothing more than a series of shallow ponds carved into the landscape. Here’s what each type actually looks like up close.
Coastal Net Pen Farms
The most recognizable type of fish farm is the open net pen, commonly used for salmon and other marine species. From above, these farms look like a grid of large circular rings floating on the water’s surface, typically arranged in two parallel rows with walkways connecting them. Each ring is made from thick, high-density polyethylene (HDPE) pipe, forming a floating collar that supports a mesh net hanging down into the water below. The nets extend roughly 30 meters deep, creating an enormous underwater enclosure that’s invisible from the surface.
From a boat, you’d see the floating collars riding low in the water, with handrails or jump nets rising a meter or two above the waterline to prevent fish from leaping out. Most farms include a central service barge or platform where feed is stored in tall cylindrical silos. Flexible pipes run from these silos out to each pen, delivering food pneumatically. On a feeding cycle, you can see pellets shooting out of nozzles above the water surface, and the water inside the pens churning as fish rise to eat. The whole operation is usually anchored in a sheltered bay or fjord where currents keep water flowing through the nets but waves stay manageable.
Earthen Pond Farms
Land-based pond farms are the simplest and oldest style, and from a distance they look like a patchwork of rectangular or irregularly shaped pools set into the ground. The water is often greenish-brown from algae growth, and the banks between ponds (called dikes) are packed earth, sometimes covered in grass. These dikes slope gradually into the water on the wet side, typically at a ratio of 2:1 or steeper, meaning for every meter of depth, the bank extends two meters horizontally. The outer, dry side of the dike can be built steeper since it doesn’t face water erosion.
Pond depths are surprisingly shallow. Most range from about 0.8 to 1.3 meters of water. The pond bottom has a gentle slope of around 1 percent from the water inlet to the outlet, allowing the entire pond to be drained for harvesting. When you see a large pond farm from the air, you’ll notice a network of channels and pipes connecting ponds to a water source, along with small concrete structures at the inflow and outflow points that control water levels.
A series of adjoining ponds shares perimeter dikes that are built strong (with clay cores to prevent seepage), while the intermediate walls dividing one pond from the next can be lighter and thinner since they hold water on both sides. The result looks something like a waffle grid cut into flat land, with each cell holding its own population of fish. Warm-water species like catfish, tilapia, and bass are commonly raised this way, with stocking densities that can range from a few thousand fingerlings per acre up to 100,000 or more for species like walleye in lined ponds.
Concrete Raceway Farms
Raceways are the most visually industrial type of fish farm. They consist of long, narrow channels, usually made of poured concrete, arranged in parallel rows that step down a hillside or gentle slope. Water enters at the top of each channel, flows through in a straight line, and exits at the far end. Picture a series of shallow, oversized bowling lanes filled with water and fish.
Individual raceway sections run up to about 100 feet long and at least 4 feet wide, though many commercial operations build them wider. The cross-section is trapezoidal, with walls that slope at 1:1 or flatter and smooth, uniform surfaces to keep water moving evenly without dead spots where waste could accumulate. At the downstream end of each section, a concrete wall called a bulkhead stretches across the channel. These bulkheads serve double duty: they maintain the desired water level using removable boards slotted into the opening, and they aerate the water as it spills over and splashes down into the next section. Some farms add splash boards or spray nozzles above the surface at these transition points, creating small waterfalls that re-oxygenate the flow.
When multiple raceways run in series down a slope, the effect is a cascading staircase of fish-filled channels. Trout and other coldwater species thrive in this setup because it mimics a flowing stream. The fish face upstream into the current, and waste is continuously flushed downstream and out. From the side, you see rows of concrete troughs, often under open-sided roof structures for shade, with clear, fast-moving water and dense schools of fish visible just below the surface.
Offshore and Submersible Cages
The newest generation of fish farms operates farther from shore in deeper, rougher water. These offshore cages are significantly larger than coastal net pens and are engineered to withstand open-ocean conditions. Some designs use massive rigid-frame spheres or cylinders made of steel and copper alloy mesh. Others use submersible gravity cages, which can sink below the surface to escape storms and strong surface currents.
Submersible cages work by flooding the outer tubes of their floating collar, causing the entire structure to descend to a calmer water layer. The process takes just a few minutes. To bring the cage back up, operators either pump compressed air into the collar or use a mechanical system that lifts a weighted sinker ring from the bottom of the net, changing the cage’s buoyancy. When submerged, these farms are essentially invisible from the surface. When floating, they look similar to conventional net pens but with heavier-duty collars and a single-point mooring line connecting each cage to an anchor on the seafloor, allowing the structure to swing freely with currents.
Feed Systems and Support Equipment
Regardless of type, commercial fish farms share certain visible infrastructure. The most prominent feature on marine farms is the feed barge: a flat, floating platform dominated by tall storage silos that can hold 3 to 4 tons of feed pellets each. Flexible hoses or pneumatic pipes radiate outward from the barge to individual pens, and blowers push feed through the system, distributing it over an area of roughly 6 by 3 meters at each pen or launching it up to 20 meters from a pond bank. In parts of Asia, feeding boats pull alongside cages with barges full of small baitfish, which are pumped through suction hoses directly into the enclosures.
On land-based farms, you’ll often see mechanical feeders mounted on posts at the edge of each pond or raceway, timed to release measured portions throughout the day. Larger operations may have centralized feed mills on-site, with conveyor belts or truck-accessible storage buildings nearby.
Sensors and Monitoring Gear
Modern fish farms are increasingly wired with technology that’s easy to overlook but present on close inspection. Underwater cameras hang inside net pens, letting operators watch feeding behavior and fish health on screens back on the service barge. Sensor probes mounted at various depths continuously track water temperature, pH, and dissolved oxygen levels. On more advanced farms, this data feeds into a central system that can automatically adjust feeding rates or trigger aeration equipment when oxygen drops.
Surface-level cameras and sometimes aerial drones monitor net integrity and predator activity. You might also see bird deterrent wires or overhead netting stretched above open pens to keep seabirds from diving in. Around the perimeter, marker buoys and navigation lights warn passing boats, giving the whole farm a visible footprint on the water that extends well beyond the pens themselves.
How Big These Operations Actually Are
Scale varies enormously. A small pond farm might cover a few acres with three or four ponds. A large commercial catfish operation in the southern United States can spread across hundreds of acres of water surface. Marine net pen farms typically cluster 6 to 20 pens in a single site, with each pen holding tens of thousands of fish. The stocking density in intensive coldwater raceways follows a practical rule: pounds of fish per cubic foot of water should be no more than half the fish’s length in inches. So a raceway full of 8-inch trout would hold about 4 pounds of fish per cubic foot. Operations focused on producing healthier fish often cut that density in half.
Extensive warm-water ponds operate on entirely different math. Walleye ponds may be stocked with 50,000 to 130,000 fry per acre, though survival rates mean actual harvests are much lower. Lined ponds, which have synthetic or clay liners on the bottom, are substantially more productive than bare dirt ponds for species like walleye, yielding 60,000 to 113,000 fingerlings per acre compared to 10,000 to 30,000 in earthen ponds.