Effect of environmental salinity on the melanotropic cells of the gilthead bream (Sparus aurata L.)

Abstract

The influence of the environmental salinity on the MSH cells of the pars intermedia in the euryhaline teleost Sparus aurata has been investigated. Control animals stayed in sea water (39/1000 salinity), and experimental fish in brackish water (7/1000 salinity) for two months. For light microscopy, pituitaries were fixed with Bouin fluid and embedded in paraffin. For electron microscopy they were fixed with Karvnosky and embedded in Araldite. Sections were stained with histochemical procedures and immunocytochemistry using an antiserum against human ACTH (1-24). The immunoreaction intensity was measured by microdensitometry, the nuclear area and granule size by planimetry, and the volume occupied by the ACTH cells by volumetry. Whereas the adaptation to brackish water decreased the immunoreactivity to anti-ACTH serum on the MSH cells, the volume and the nuclear area of these cells increased although without statistical significance. These results suggest that the adaptation to hypoosmotic environment elicits an increase in the synthesis and release of MSH and ACTH.