Responses of the per iodic acid schiff positive pars intermedia cells in the cichlid fish sarotherodon mossambicus to ambient calcium and background adaptation

Van Eys, G.J.J.M.; Wendelaar Bonga, S.E.

Cell and Tissue Research 236(1): 181-188


ISSN/ISBN: 0302-766X
Accession: 006329477

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The function of the PAS[periodic acid-Schiff]-positive pars intermedia cells in fish has been connected with control of background adaptation and of plasma Ca levels. Since background reflectivity and illumination influence Ca metabolism in S. mossambicus, the hypothesis that the effects of background reflectivity on the PAS-positive cells are mediated by changes in plasma Ca was tested. However, total plasma Ca does not correlate with the activity of the PAS-positive cells as estimated by morphometrical criteria. Transfer of S. mossambicus to a white background leads to a drop in plasma Ca, and a marked reduction of the activity of the PAS-positive cells. Adaptation to low Ca freshwater, on a neutral background, has the same effect on plasma Ca but has no effect on the PAS-positive cells. The characteristic structural features of highly active PAS-positive cells in fish from a black background are not due to the slight hypocalcemia that occurs in these fish, since addition of Ca to the water in concentrations that fully prevent the drop in plasma Ca does not suppress the PAS-positive cells. These findings make it very unlikely that these cells produce a hypercalcemic factor in S. mossambicus.