Seawater challenge test and body composition of coho salmon (Oncorhynchus kisutch)

Investigations of the adaptability of two growth groups of coho salmon fry (1+ and 0+) while being transferred from freshwater (FW) into seawater (SW) were performed in the season autumn/winter on four locations (three locati ons in the Adriatic Sea and one in the FW fish farm, Luknja). Average weigh t of the 1+ group was 116 g, and average weight of the 0+ group was 86 g. C hanges in body composition and condition factor were examined immediately p rior to SW transfer, during the early stages of smoltification and for a pe riod of 30 days post-SW transfer. Fish samples (n = 10/time point) were tak en in FW, during the transport, and after the transfer into the sea (22.5, 45 and 90 min; 3, 6 and 12 hours, and also 1, 2, 4, 8 and 30 days following the transfer). Results from the experiments demonstrate some differences i n the adaptive fitness between the two age groups examined, with inferior a daptation being expressed by the 0+ group. Over the period of investigation s an increase in body moisture and decreases in body lipids and proteins we re observed, when compared against FW controls regardless of smolt age. Thi s might be interpreted as indicating malnourishment due to aphagia, since a ppetite loss has been described in this, and other oncorhynchids during SW transfer.