Prawns are sexy. Prawns are expensive! Everyone loves prawns! Newcomers to the aquaculture or aquaponics fields jump to the conclusion that prawns will make them the most money of any species. Seeing that they sell for $10/lb when tilapia sells for $4 or $5/lb inspires them; they ignore the business reality that if it was that easy to do, everyone would be doing it. We'd have lots of prawns, and the price would only be $2/lb. There are places in the South Pacific that are like that: the locals don't eat the lobster because there's so darn much of it, they would rather eat the reef and ocean fish.
The problem with this kind of thinking is that it ignores all the natural behavior, breeding habits, and other facts about prawns that one must know to be able to raise them successfully. A 5,000 gallon fish tank that can easily hold 1,500 pounds of tilapia will house 50 prawns at best, or about 4 pounds.
Prawn Behavior:
There are several things you must know to successfully raise prawns in an aquaponic system. Tilapia will eat the prawns, so you need to keep the prawns separated from the fish in different tanks or troughs. Everyone likes to eat prawns, even other prawns. To raise prawns commercially, breeders stock PL's (Post Larvae, or juvenile prawns) at 3 to 4 per square yard of pond space, and harvest 1 to 2 per square yard of pond space.
The reason they are only able to harvest half of the prawns they stock is that the prawns are territorial and fight with and eat each other. A lot of the mortalities come from large prawns being eaten by smaller prawns when the larger ones are molting and unable to protect themselves because their shells are quite soft for a long time during the molting process. The only way to successfully raise prawns commercially is to have tens or even hundreds of acres of pond space, and even then success is difficult to achieve because the prawns are verysusceptible to disease, and predation by human thieves.
The reason prawns work in an aquaponics system is that they are detrivores. This means they eat organic garbage: anything that falls to the bottom of the troughs; a dead mosquito fish, some roots that fell off a plant, another prawn that just died or was drygulched by a group of prawns while molting. As a result of this feeding behavior, we don't need to feed them anything, and having prawns in the system does not increase the amount of feed we need to purchase. Our opinion is that in the process of eating the detritus of dead roots and other organic refuse that falls to the bottom of the troughs, they further break up this stuff and liberate nutrients that the plants thrive on, as well as add their own excreta to the system, which then turns into nutrients for the plants in the system.
As mentioned, the prawns are raised in the hydroponic troughs under the vegetables to keep the tilapia from eating them. We have never seen any damage to vegetable roots caused by prawns, or any decrease in system vegetable production after we introduced prawns to one of our systems. In fact, we have noticed that the smaller ones will shelter in particularly large root groups, and come zooming out when you lift a raft to inspect the roots.
You CAN Make Money With Prawns:
I know a prawn farmer in Honduras, and she makes money raising prawns. But she has 600 acres of ponds, expert labor that costs her $6/day, an $8/pound price for her prawns (she ships them to Europe), and says if her operation was any smaller, she couldn’t make a go of it.
When we raised prawns in our aquaponics troughs, we stocked 300 or so PL's into a total of 864 square feet of hydroponics troughs in a commercial system (a stocking density of 3 per square yard), and 4 months later harvested 20-30 lbs of prawns from that system. These prawns can be sold off the back of the truck for $10/lb in Hawaii. So this would total 60-90 lbs of prawns a year (or $600 to $900 of gross income) from a system that produces 4,500 lbs of organic lettuce at $5.92 a pound ($26,732) and 600 lbs of tilapia at $5/pound ($3,000), per year. You can see that the prawns are not the largest or even the second largest system output.
Next newsletter: Part 2 of "Prawns Revisited", with more information on how to breed your own prawns and where to get PL's to stock your system with.
The photo below is our Solar Greenhouse. It's cool when it's hot, and warm when it's cold (hope that makes sense to you, it's the best greenhouse we've ever seen!).
The problem with this kind of thinking is that it ignores all the natural behavior, breeding habits, and other facts about prawns that one must know to be able to raise them successfully. A 5,000 gallon fish tank that can easily hold 1,500 pounds of tilapia will house 50 prawns at best, or about 4 pounds.
Prawn Behavior:
There are several things you must know to successfully raise prawns in an aquaponic system. Tilapia will eat the prawns, so you need to keep the prawns separated from the fish in different tanks or troughs. Everyone likes to eat prawns, even other prawns. To raise prawns commercially, breeders stock PL's (Post Larvae, or juvenile prawns) at 3 to 4 per square yard of pond space, and harvest 1 to 2 per square yard of pond space.
The reason they are only able to harvest half of the prawns they stock is that the prawns are territorial and fight with and eat each other. A lot of the mortalities come from large prawns being eaten by smaller prawns when the larger ones are molting and unable to protect themselves because their shells are quite soft for a long time during the molting process. The only way to successfully raise prawns commercially is to have tens or even hundreds of acres of pond space, and even then success is difficult to achieve because the prawns are verysusceptible to disease, and predation by human thieves.
The reason prawns work in an aquaponics system is that they are detrivores. This means they eat organic garbage: anything that falls to the bottom of the troughs; a dead mosquito fish, some roots that fell off a plant, another prawn that just died or was drygulched by a group of prawns while molting. As a result of this feeding behavior, we don't need to feed them anything, and having prawns in the system does not increase the amount of feed we need to purchase. Our opinion is that in the process of eating the detritus of dead roots and other organic refuse that falls to the bottom of the troughs, they further break up this stuff and liberate nutrients that the plants thrive on, as well as add their own excreta to the system, which then turns into nutrients for the plants in the system.
As mentioned, the prawns are raised in the hydroponic troughs under the vegetables to keep the tilapia from eating them. We have never seen any damage to vegetable roots caused by prawns, or any decrease in system vegetable production after we introduced prawns to one of our systems. In fact, we have noticed that the smaller ones will shelter in particularly large root groups, and come zooming out when you lift a raft to inspect the roots.
You CAN Make Money With Prawns:
I know a prawn farmer in Honduras, and she makes money raising prawns. But she has 600 acres of ponds, expert labor that costs her $6/day, an $8/pound price for her prawns (she ships them to Europe), and says if her operation was any smaller, she couldn’t make a go of it.
When we raised prawns in our aquaponics troughs, we stocked 300 or so PL's into a total of 864 square feet of hydroponics troughs in a commercial system (a stocking density of 3 per square yard), and 4 months later harvested 20-30 lbs of prawns from that system. These prawns can be sold off the back of the truck for $10/lb in Hawaii. So this would total 60-90 lbs of prawns a year (or $600 to $900 of gross income) from a system that produces 4,500 lbs of organic lettuce at $5.92 a pound ($26,732) and 600 lbs of tilapia at $5/pound ($3,000), per year. You can see that the prawns are not the largest or even the second largest system output.
Next newsletter: Part 2 of "Prawns Revisited", with more information on how to breed your own prawns and where to get PL's to stock your system with.
The photo below is our Solar Greenhouse. It's cool when it's hot, and warm when it's cold (hope that makes sense to you, it's the best greenhouse we've ever seen!).