One of the world's most commonly farmed fish, tilapia are typically raised in square pens and get fed by hand a few times a day. New Brazilian technology that does away with those factors, however, is claimed to reduce both expenses and fish mortality rates.
Developed by the Fisher Piscicultura aquaculture company, the system consists of wire mesh circular pens that are 4.5 m deep and 12 m in diameter (14.7 by 39.3 ft), each of which is housed within an aluminum frame. These pens/frames float on the surface of a lake or river, buoyed up by a ring of PET (polyethylene terephthalate) bottles.
In the center of each pen is a fish-feed silo, which is equipped with a solar-powered timer. That silo contains 1,200 kg (2,646 lb) of feed, which gets automatically dispensed in relatively small amounts 48 times a day.
According to the designers of the system, feeding the tilapia so often keeps them satiated, causing them to eat less overall than they would if they gorged themselves at just three or four daily feedings. This should allow farm operators to save money on the cost of food, plus it ought to reduce the amount of excrement produced by the fish, and allow them to digest their food better.
Additionally, when a batch of tilapia reach a certain size, they ordinarily have to be netted out of one pen and transferred into another, to make way for a new batch of smaller, younger fish. This involves removing them from the water for a short period, which stresses them out, causing some of them to die.
By contrast, in the new system, they can be transferred between pens without leaving the water. This is accomplished by inserting a floating wedge-shaped mesh container into the pen, then using a pivoting gate to drive the fish into that container. It is then simply floated over to another pen, which the fish are released into. It's kind of hard to describe, but the setup can be seen in use, in the video at the bottom of the page.
"Tilapia mortality exceeds 20 percent on most conventional fish farms," says company partner David Pulino. "Our own rate is currently 8 percent, but our goal is to lower it to 3 percent to 5 percent maximum."
As an added bonus, when it's time to remove freshwater mussels from the empty pen, air is pumped into a drum located at the bottom, causing the whole thing to rise up out of the water (see photo above). In the case of traditional pens, they have to be raised by a crane, or scuba divers have to be sent in.
Having been in development for the past several years, the Fisher Piscicultura system is now undergoing final testing in a reservoir behind Brazil's Água Vermelha hydroelectric dam. Funding for the project is being provided by the FAPESP agency's PIPE small business support program.
Sources: FASEP, Fisher Piscicultura
