Effects of Elevated Plasma Cortisol on Growth Rate of Anadromous Brook Charr (Salvelinus fontinalis)

Ian Kinahan, Luis Vargas-Chacoff, Stephen D. McCormick

IntroductionCortisol is a glucocorticoid hormone produced by the adrenal gland and released into a fish’s blood stream in response to stress. The impacts of cortisol on many aspects of the physiology of fish is unknown, including its impact on growth. In this this study, we assessed the effects of elevated plasma cortisol on the growth rate of a model species, anadromous brook charr.

Brook charr are endemic to Eastern North America, and have been introduced successfully in the West. This species is of both recreational and commercial importance; thus making its physiological response to artificially elevated plasma cortisol levels of significant conservation importance.

Methods Results

Future Directions•Analysis of plasma samples: Cortisol and osmolality levels.•Analysis of gill biopsies for Na+K+-ATPase activity.•All remaining charr have been transferred to sea water for another 30 days•Cortisol is predicted to increase growth rate in sea water•Gill biopsies and blood samples will be taken again in order to measure physiological success.

Conclusions•Growth rate is negatively affected by cortisol injection, with higher doses showing the greatest effect.•Condition factor was lower in cortisol treated fish, suggesting that lipid content was also reduced. •Hematocrit was not significantly affected by cortisol treatment.

Figure 1. Growth rate (weight) in S. fontinalis treated with vehicle (control) and increasing doses of cortisol (8.25, 25, 100 µg/g body weight) at day 30 after injection. Values are mean + SEM. Different letters indicate significant differences between experimental treatment (One way ANOVA, Tukey-Test, P<0.05).

Figure 3. Condition factor (K) in S. fontinalis treated with vehicle (control) and increasing doses of cortisol (8.25, 25, 100 µg/g body weight) at day 30 after injection. Values are mean + SEM. Different letters indicate significant differences between experimental treatment (One way ANOVA, Tukey-Test, P<0.05).

Figure 4. Hematocrit (red blood cell volume) in S. fontinalis treated with vehicle (control) and increasing doses of cortisol (8.25, 25, 100 µg/g body weight) at day 30 after injection. Values are mean + SEM. No statistically significant difference across all treatment groups.

Figure 2. Change in weight in S. fontinalis treated with vehicle (control) and increasing doses of cortisol (8.25, 25, 100 µg/g body weight) 10, 20 and 30 days after injection. Values are mean + SEM. Different letters indicate significant differences between experimental time at same experimental condition. Different symbols indicate significant differences between experimental condition at the same experimental time (Two way ANOVA, Tukey-Test, P<0.05).

2. Cortisol was suspended in a slowrelease vehicle and injected in amounts of 0 (vehicle), 8.25, 25 and 100 (μg/ g body weight) to 4 groups of 20 fish.

Cortisol

PIT tags

3. Each 10 days, for 30 days total, length and weight measurements were made.

4. On day 30, gill biopsies and blood samples were acquired for analysis. After 7 days, the fish were transferred to sea water.

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1.PIT tags were surgically implanted in 80 brook charr.