Net cage farming of salmonids is a huge and
growing industry especially in countries like Norway where environmental
conditions (deep oligotrophic fjords) favor this type of production. In
comparison, net cage production in eutrophicated regions like Denmark is more
challenged depending on the exact location and local current conditions, and
new measures are requested.
As it is now, solid and dissolved waste nutrients
from net cages (consisting primarily of organic matter, phosphorus, and
nitrogen) dilute and disperse in the sea with no further treatment. All net
cage waste traces directly (via feed spill) and indirectly (via fish excretion
and faces) to fish feed, and fish feed modifications therefore have a huge
impact on especially waste nutrient quantities and to some extent also on solid
fecal physical structure.
Aiming at improving net cage sustainability
by eventually collecting fish feces from cages, the objective of the current
project is to resolve if - and to what extent - fish feed manipulations may
improve fish feces coherency, density, and sinking velocity making them easier
to collect. To resolve this, a number of controlled experiments are needed.
Procedures for measuring fecal pellet coherency, density, sinking velocity
(e.g., video recording), and nutrient leakage will be developed in the lab. The
methods will be applied to controlled feeding trials with large
(> 700 g) all-female rainbow trout maintained in the lab and fed different
I samarbejde medAquaPri, BioMar, Hvalpsund Net, the Danish Aquaculture Association