Liver of the brown trout, Salmo trutta (Teleostei, Salmonidae): a stereological study at light and electron microscopic levels.
A quantitative study was undertaken for the first time on the normal liver of male and female 2-year-old brown trout, Salmo trutta.



Liver was fixed by controlled perfusion. Organ-level morphometry provided weight and volume. A two-stage stereological approach was performed at light and electron microscopy levels. Systematic sampling and point-counting morphometry were used for estimating the relative volumes of the structural compartments. Total absolute volumes of these components were obtained by multiplying each volume density by the volume of its reference space.



Liver volume was 3,423.6 mm3 for males and 3,657.4 mm3 for females. Parenchyma accounted for 95% of hepatic volume. Veins and bile ducts occupied, respectively, 76% and 17% of the stroma, whereas arteries, connective tissue, and melanomacrophages together composed only 6%. Hepatocytes occupied 88% of the parenchyma. Nonhepatocytic cells (endothelium, biliary epithelial cells, Ito cells, and macrophages) composed 4% of the parenchyma, the capillary lumen 6%, and other spaces (Disse space, canaliculi, and lumina of preductules and ductules) composed 2%. Significant sexual differences were found: (1) Females showed a greater parenchymal volume density (0.85% vs. 0.35%) and absolute volume (29.5 mm2 vs. 11.7 mm3) of Ito cells; (2) macrophages of females also presented a greater parenchymal volume density (0.94% vs. 0.46%), but not absolute volume.



The need to analyze both relative and absolute stereological data was stressed. Similarities and differences were detected between brown trout and other species (fishes and mammals); the findings suggest that, despite architectural differences, some quantitative parameters of liver microanatomy were retained during phylogeny. Factors mediating sexual differences in Ito cells and macrophages were discussed and the need for further studies was highlighted.
Rocha
E
E
Institute of Biomedical Sciences Abel Salazar, University of Oporto, Porto, Portugal.
Monteiro
R A
RA
Pereira
C A
CA
D000818:Animals; D001652:Bile Ducts / Q000033:anatomy & histology / Q000648:ultrastructure; D001835:Body Weight; D004727:Endothelium / Q000033:anatomy & histology / Q000648:ultrastructure; D004848:Epithelium / Q000033:anatomy & histology / Q000648:ultrastructure; D005260:Female; D008099:Liver / Q000033:anatomy & histology* / Q000098:blood supply / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D009929:Organ Size; D012737:Sex Factors; D014337:Trout / Q000033:anatomy & histology*