BECKMAN, BRIAN; SHIMIZU, MUNETAKA; GADBERRY, BRAD; PARKINS, PAUL; COOPER, KATHY; National Marine Fisheries Service; University of Washington; University of Washington; National Marine Fisheries Service; University of Washington: Temperature and the relations among plasma IGF-I, 41 kDa IGFBP, and growth in coho salmon.

The effects of environmental variation on the IGF-I system and subsequently on growth have yet to be fully elucidated in piscine systems. Here we describe an experiment that examined the effects of temperature on IGF-I and 41 kDa IGFBP levels. In June 2001, 280 yearling coho salmon were selected from a group of previously PIT-tagged (January 2001) fish. These fish were placed in four 1.3m circular tanks and fed a ration of 1% body weight/day. After 1 week the water temperature in two tanks was reduced from 11oC to 6.5oC. Subsequently feeding rates were 1.5 and 1% body weight/day in the 11oC tanks and 1 and 0.5% body weight/day in the 6.5oC tanks, resulting in four treatments (WarmHi, WarmMed, CoolMed, and CoolLow). All fish were measured at two week intervals over the next two months. A sub-sample of 10 fish/tank was obtained at two week intervals, plasma collected, and plasma IGF-I and 41 kDa IGFBP were measured by RIA. There appeared to be an immediate decrease in IGF-I levels after temperatures decreased, followed by an acclimation to the decreased temperature. 41 kDa IGFBP levels increased following the temperature decrease and remained elevated for several weeks. There was a significant, positive relation between growth and plasma IGF-I for the fish held at 11oC on all four sampling dates (r2>0.4). For fish held at 6.5oC, there was no relation between growth and IGF-I on the first two sampling dates after the temperature decrease. Subsequent samples revealed a similar relation between IGF-I and growth for fish held at both 11 and 6.5 oC (no significant difference between slope and intercept).