Effect of Fasting on Pituitary Growth Hormone Expression and Circulating Growth Hormone Levels in Striped Bass

The mechanisms controlling the circulating levels of growth hormone (GH) during periods of starvation in fish are not well defined. In this study, the effect of fasting on GH release and pituitary messenger RNA (mRNA) expression in striped bass Morone saxatilis was examined. Over a 4‐week period, the body mass of striped bass fed to satiety increased 22.9%, while that of fasted fish decreased 17.3%. The plasma GH concentrations of fed fish remained low throughout the experiment, but those of fasted fish increased significantly (P < 0.001) after 2 and 4 weeks. The striped bass that were fasted for 2 weeks demonstrated a 33% increase (P = 0.10) in GH mRNA expression compared with those fed to satiety. These data confirm that short‐term fasting in striped bass increases their circulating levels of GH in a manner similar to that experienced in other species of fish. This study also demonstrates—for the first time in a fish species—that pituitary GH mRNA expression increases during fasting, which suggests a corresponding increase in pituitary GH synthesis. Further research will be necessary to determine whether a direct correlation exists between increased expression and increased release during starvation.