The effect of temperature change on the relations among plasma IGF-I, 41-kDa IGFBP, and growth rate in postsmolt coho salmon

Abstract

The effect of temperature change on the relations between growth and plasma levels of insulin-like growth factor-I (IGF-I) and 41-kDa insulin-like growth factor binding protein (41-kDa IGFBP) were assessed in postsmolt coho salmon. An experiment was initiated by reducing the temperature from 11 to 7 °C for two groups of fish that were subsequently fed at either 0.5% or 1.0% body weight per day. Two additional groups of fish were maintained at 11 °C and fed either 1.0% or 1.75% body weight per day. Fish were weighed and measured, and plasma samples were obtained on four dates: 12, 27, 47, and 63 days after the temperature change. Plasma IGF-I values were significantly lower in cool water groups than warm water groups for the first sample, by the last sampling, there were no significant differences between groups. There were no significant differences between treatment groups for plasma 41-kDa IGFBP levels for the first sampling. Subsequently, significant differences in plasma 41-kDa IGFBP levels between fish fed at different levels, regardless of temperature, were found. On all dates, significant associations were found between growth, plasma IGF-I, and 41-kDa IGFBP for fish held in warm water; however, no such relations were found for fish held in cool water for the first two sampling dates. After 47 and 63 days in cool water, significant relations between growth, plasma IGF-I, and 41-kDa IGFBP were reestablished. These data suggest that associations between growth, plasma IGF-I, and 41-kDa IGFBP were disrupted by a temperature decrease for at least 4 weeks. However, significant relations were reestablished after 47 days of temperature acclimation. These results support further investigation of plasma IGF-I and 41-kDa IGFBP as growth indicators in fish.