Journal of Aquaculture Research & Development

Water quality and fish welfare in closed floating cages for production of Atlantic salmon (Salmo salar)

International Conference on Aquaculture & Fisheries

July 20-22, 2015 Brisbane, Australia

Arve Nilsen1, Asbjørn Bergheim2, Hildegunn Viljugrein1, Kristoffer Vale Nielsen1 and Martin Haugmo Iversen3

Posters-Accepted Abstracts: J Aquac Res Development

Abstract:

In Norwegian salmon farming, closed floating sea-cages have been introduced as a possible solution to the increasing problems with infestation of sea-lice and as a way to minimize the risk of fish escapes. Closed cages could also make it possible to remove and utilize a substantial part of the solid waste otherwise released directly to the marine environment. It is also expected that more controlled rearing conditions compared to in traditional open cages could lead to better survival and a more effective production. So far, little is known about how to safeguard and optimize the production of fish in such closed floating cages. A pilot project was initiated in spring 2012 stocking a closed cage of 1550 m3 volume with 80 000, 1-year old salmon smolt. We concluded that the closed system was fit to eliminate the problems with sea-lice, and the fish stock demonstrated relatively high survival rate (97.1%), acceptable growth and welfare score. However, the water exchange rate was too low during the end of the cycle in autumn at a fish density of 20 ? 25 kg/m3 resulting in reduced water quality and fish welfare. From November 2012 to September 2014, on-growing of Atlantic salmon from sea-transfer to harvest size in closed cages of 3000 m3 was studied and compared to parallel groups in open net-cages. Appearance of sea-lice, fish mortality and causes of mortality, water quality and other fish welfare parameters were frequently monitored. No infestation with sea-lice was detected during 28 months of trials. The survival rate varied between groups, but was generally higher than in the open reference cages. Growth and feed conversion rate was acceptable, but should be further improved. We established a first generation model for the interaction between specific water consumption (Q=l/kg fish/min), feeding intensity (L=g feed/m3 water flow), important water quality parameters, such as pH, CO2, TAN, suspended solids (SS), and fish welfare in closed cages.