The role of growth hormone in the adaptability of Atlantic salmon (Salmo salar L.) to seawater: effects on the morphology of the mucosa of the middle intestine

Abstract

Ultrastructural modifications of the middle intestine of the salmon, Salmo salar, induced by transfer to seawater have been studied in two groups of fish: the first group received sham treatment and the second was treated with ovine growth hormone (oGH). In sham-treated fish during the first 2 days in seawater, significant distension of the intercellular spaces was observed between the apical tight junction and the basement membrane. In the basal part of the enterocytes, tubular invaginations in the intercellular spaces were closely associated with mitochondria. In oGH-implanted fish, we observed no signs of modification of the ultrastructure of the mucosa. There were no dilatations of the intercellular spaces and no infoldings in the basal part of the enterocytes. After 7 days in seawater, the mucosa of the intestine of sham- and oGH-treated fish was quite similar. The effects of oGH treatment were clear, and treatment seemed to provoke "pre-adaptation" of the intestinal mucosa before exposure to high salinity to maintain the morphology of the middle intestine of Atlantic salmon abruptly transferred to seawater.