Output of organic material from land-based juvenile Atlantic cod (Gadus morhua) tanks

Abstract

A mass balance experiment was conducted in which dry mass, dissolved organic carbon, total nitrogen, lipid classes, and fatty acids were quantified in the inflow and outflow of land-based juvenile Atlantic cod (Gadus morhua) tanks. The inflow contained 89.9 ± 15.4 g/day of dry mass that increased to 187 ± 39 g/day in the outflow. Correction for the inflow indicated 96.8 ± 33.8 g/day of excess feed and faeces left the tanks amounting to a feed to waste conversion ratio of 25 %. The amount of feed in the waste was estimated to be 3 %. The breakdown indicator free fatty acid (43.1 ± 9.5 % total lipid), the markers of zooplankton and subsequent indicators of the feed, 20:1ω9 and 22:1ω11, and the essential fatty acid docosahexaenoic acid (DHA) were all significantly higher (p < 0.020) in the outflow compared to the inflow. The output from the entire aquaculture facility was calculated from the experimental tanks and gave 1,060 ± 370 g/day dry mass and 1.5 ± 0.4 g/day DHA, which could support 0.44 tonnes of mussels assuming an average weight of 5.31 g/mussel. Additionally, the output data were calculated per kilogram of fish and used to estimate potential output for operational Atlantic cod farms. An 1,880 tonne farm would produce 3,170 ± 870 kg/day dry mass and 4.7 ± 1.7 kg/day of DHA, which could theoretically support 1,400 tonnes of mussels. Natural mussels and those grown in co-culturing systems could assimilate such valuable compounds that would otherwise be lost.