Clonidine Mects Growth Hormone and Growth in Juvenile Coho Salmon Oncorhynchus kisutch

Growth hormone concentrations in juvenile cocho salmon were determined after intraperitoneal injections (yearlings; age 1+) and oral treatments (yearlings and fry; age 0+) with clonidine. Weights and lengths were also measured in coho juveniles fed diets supplemented with clonidine.
Plasma growth hormone concentration increased significantly (78.2%) 24 h after injection. Yearlings fed clonidine showed a significant increase (136%) in plasma growth hormone after 14 days, and levels remained elevated through 28 days (116%) before dropping to control levels at 42 days. Coho yearlings fed clonidine showed no significant increase in growth compared to controls after 56 days of treatment, but coho fry were significantly heavier (33%) and longer (8%) after 70 days.