Hello again! Last week we focused on RAS, or Recirculating Aquaculture Systems, one of the four major types of aquaculture. This month, we’re covering a second type which you might be more familiar with; Fish Cage Aquaculture. If you don’t recognize the name, you might know it by another, as this method is rather common and goes by a variety of names, including Net Pen Aquaculture or simply Cage Culture. If that doesn’t ring a bell, there’s still a good chance you might recognize the method based on sight.
Modern Fish Cage Aquaculture has mesh, typically circular pens placed in open bodies of water such as the ocean, rivers, lakes, and even large ponds. These mesh enclosures allow for the free flow of natural water while keeping the aquatic life contained.
The frames of these mesh pens are completely rigid only around the top, and are designed to float, so this is the part that can be seen from the water’s surface. The rest of the cage is submerged, anchored to the bottom of the water body.
As with any aquaculture method, we need to be thoughtful about the good and the bad. While water quality must still be monitored, much of the labor that goes into maintaining an optimal environment for Cage Culture is handled by the natural current in open water. This flow of water maintains oxygen levels and rids the enclosures of waste, meaning less infrastructure is needed compared to other methods. Another benefit is that Cage Culture can be used. In some cases, these cage farms can exist within bodies of water for human use like irrigation or livestock watering, or for recreation like swimming, fishing, or boating.
When it comes to harvesting the seafood, it is a fairly straightforward process. When you want a certain quantity of fish, the pen nets are simply pulled to shallower water, and the contents tipped out. This allows the farm to select how many and which fish are desired, making harvesting possible for everything from large markets to smaller scale personal consumption.
Some of the challenges with Cage Culture are also due to the use of the natural environment. Though the cages can hold a large number of fish comfortably, having that many fish in one space means you have to watch out for potential pollution in the environment due to excess nutrients from farm waste. In addition, disease outbreaks are not uncommon, and due to the close proximity of the fish, an entire farm can easily be infected. Relatedly, while said diseases can come from wild fish, the opposite can also be true, especially as farmed fish can escape and enter the natural environment. Escape is also problematic if the farmed fish have genetics different than that of their wild counterparts. This can lead to cross-breeding and the reduction of genetic diversity.
Predation is also a huge concern. Having a large number of fish concentrated in one area is a beacon for any creature that likes to snack on whatever you are raising, and can be quite creatively destructive in attempting to get to the fish. However, many of these concerns with Cage Culture can be mitigated with careful forethought as to location (which we’ll talk more about next month). In addition, there may be a variety of aquaculture regulations to help deal with region specific concerns and can be dependent on the species being farmed.
Fish Cage Aquaculture is often used to raise trout, salmon, tilapia, or sunfish, but can hold shrimp and even mollusks like oysters as well. Here in Maryland, Cage Culture systems are mainly used for catfish, striped bass, and hybrid striped bass (the latter of which we’ll cover in a later newsletter this year, so keep an eye out). As aquaculture advances alongside technology, new cage methods are being tested. Particularly as this is one of the most common methods, just as it goes by a variety of names, so too does it have a growing variety of cage systems beyond pen net. If you’re interested in diving deeper into this type of aquaculture, definitely check out submerged, submersible, and fixed cages as well, which have slightly different methods.