Closed-cage smolt experiment pays off
Salmon grown to 800 grammes in a floating closed cage experienced no lice and had higher survival compared to smolt put straight into open cages, a company testing the technology has revealed.
Norwegian salmon farmer Sulefisk has completed a full production cycle from smolt put out at 130 grammes in the Ecomerden - or EcoCage - closed cage, followed by stays in open cages until slaughter.
The Ecomerden's maker, also called Ecomerden, said: “There are numerical values over an entire generation, and this is a milestone for closed cages versus open cages.”
The results come as the University of Stirling's Institute of Aquaculture prepares to start its own nine-month study on the feasibility of growing up to 1 kg in floating closed-cage nurseries in Scotland. The project has been commissioned by the Scottish Aquaculture Research Forum, which hopes such a method can lead to salmon spending less time in open pens for the final growing stage, reducing their exposure to sea lice and disease.
High survival
In a press release on its results, Ecomerden said: “The smolt from the hatchery went out into the Ecomerden at 130 grammes, and were grown to approximately 800 grammes without seeing any sexually mature female lice and without any kind of lice treatments. For the last phase before slaughter they went on a site with open cages.
“Pancreas disease (PD) and amoebic gill disease (AGD) were detected at the open cage site, but the fish from Ecomerden continued to grow with high survival dramatically greater than the fish in open cages.
“Forty per cent of post smolts from Ecomerden grew to 4.9 kg over 53 weeks with 3.3% mortality throughout the sea phase, including the Ecomerden phase.”
High pigment values
The residual biomass in the open cage went through a mechanical delousing upon removal of the first slaughter batch, with 0.8% mortality. Slaughtered fish had an average of 92-95% superior quality with extremely high pigment values well above what was expected. The fish were also in very good condition, a factor which in turn provided a good outcome at harvest.
“In relation to the reference fish that went out in open cages directly from the hatchery, there was a big difference in survival.”
Despite PD and AGD, the mortality of post-smolt from the closed cage was only in the order of 5-10 fish each day, which, compared with an average site (about 20%), is reduced to below 5% throughout the sea phase, said Ecomerden.
Ecomerden is a self-contained closed cage construction where the floating collar is a rigid steel frame designed to withstand strong conditions. All necessary equipment is built into and protected by the float collar.
The heavy duty flexible wall is specially designed and constructed by French manufacturing group Serge Ferrari, a leader in flexible composite materials. There is also a net inside the Ferrari wall.
