A stereological study along the year on the hepatocytic peroxisomes of brown trout (Salmo trutta)

Studies on peroxisomes of fishes are very scarce, and the influence of both gender and season on their morphology is virtually unknown. A stereologica l approach was then performed on the hepatocytic peroxisomes of 3-year-old brown trout. Males and females were collected in February tend of spawning season), May (early vitellogenesis), and September (advanced vitellogenesis ). Liver was fixed by perfusion, and tissue was processed for catalase cyto chemistry. Manual stereology was used on electron microscopic photographs f or estimating relative volumes, surfaces and numbers of peroxisomes. Their mean surface, volume and spherical equivalent diameter were secondarily der ived. Total volume, surface and number of peroxisomes per hepatocyte were a lso computed (cell volume being used as intermediate value). AU parameters relative to size displayed statistical significant changes, generally by se ason and gender interaction; seasonal changes were more pronounced in Femal es. In February and in September female peroxisomes were smaller and had le sser total volumes and surfaces than in males; in May, both genders were vi rtually identical. No statistically significant results were obtained in re lation to peroxisome number. Strong negative correlations were found betwee n all the size parameters of female peroxisomes and the gonado-somatic inde x (GSI). In males, only peroxisomal diameter, surface and volume were signi ficantly but fairly positively correlated with the GSI. Similarities and di fferences existed between brown trout and other species. It was firstly dem onstrated that changes in size can occur without modifications in number. I n one male, however, unusually large and fewer peroxisomes with loops prove d that in brown trout size and numerical changes can occur simultaneously t oo. Functional implications of morphological data were highlighted, includi ng possible relationships between steroid hormones and peroxisomes.