Consumption and assimilation of salmon net pen fouling debris by the Red Sea cucumber Parastichopus californicus: Implications for polyculture

Fouling debris composed of fish feces, excess fish food, algae, and other particulate organic matter can create environmental problems for aquaculture facilities that rear fish in ocean net pens. Accumulations of organic debris can clog the nets and restrict water circulation which in turn can stress fish. Experiments in which red sea cucumbers Parastichopus californicus were allowed to feed inside floating net pens at a salmon rearing facility in Southeast Alaska showed that sea cucumbers consumed fouling debris and cleared a significant amount of surface area on the nets (P < 0.0001). Sea cucumbers assimilated amino acids and other organic matter from fouling debris two to three times more efficiently than from their natural sediment diet. Muscle development of sea cucumbers consuming fouling debris inside the net pens was also significantly greater than that of sea cucumbers feeding in their natural environment (P < 0.0003). This work suggests that polyculture operations in which commercially important detritivores, like the red sea cucumber, are grown in net pens along with salmon could possibly convert the net from self-fouling to self-cleaning and could turn fouling debris into a marketable product (sea cucumber biomass).