Inter lake comparison of liver morphology and in vitro hepatic monodeiodination of L‐thyroxine in sexually mature coho salmon, Oncorhynchus kisutch Walbaum, from Lakes Erie, Ontario, Michigan and Superior

Abstract

The hepatosomatic index (HS1) of female sexually mature coho salmon, Oncorhynchus kisutch, from Lake Superior was significantly higher (P<0.01) than in males, whereas that of females from Lake Erie was significantly lower (P<0.05) than in males; there was no significant sex differences in coho salmon from Lakes Ontario or Michigan. Hepatic nuclear areas (HNA) were significantly higher (P<0.01) in males compared with females in fish collected from Lakes Ontario and Erie, but there was no sex differences in HNA of coho salmon from Lakes Superior or Michigan. In all four lakes, hepatocyte cytoplasmic volume was significantly higher (P<0.01) in males than in females from the same lake, and the cytoplasmic volume: nuclear volume ratio of males was corresponding significantly higher (P< 0.05) than in females from the same lake.Two hepatocytic cell types were evident, termed' light and dark cells, based on the electron density of their cytoplasmic matrix. There were considerable intersex and interlake differences in the relative populations of light ‘and dark’ cells in coho salmon from Lakes Ontario, Michigan, Erie and Superior, and also in the hepatocytic content of lipid, glycogen, mitochondria and ribosomal and smooth endoplasmic reticulum.There were no sex differences with regard to in vitro hepatic monodeiodination of L‐thyroxine (T4) to triiodo‐L‐thyronine (T3) in salmon from any of the lakes. However, T4 to T3 conversion was significantly lower (P< 0.05) in liver homogenates prepared from Lake Ontario coho salmon than in comparable preparations of liver from Lake Superior, Lake Erie, or Lake Michigan salmon.