ADAPTIVE-CHANGES OF LIVER COMPOSITION AND STRUCTURE IN GOLDEN IDE DURING WINTER ACCLIMATIZATION

The present investigation was designed to study hepatic alterations in fish during the winter period and to compare them with acclimation phenomena in fish subjected to fluctuating environmental variables in the laboratory. Immature young‐of‐the‐year golden ide, Leuciscus idus melanotus, were kept in an outdoor pond from September to April. Liver response was analyzed using histological, morphometrical, and biochemical methods. In a first phase from September to March, hepatocellular activity was reduced without evidence of disturbance of liver functions. Cell size, energy reserves, and protein contents as well as mitochondrial number and volume decreased significantly; RNA contents were moderately reduced. Cellular compartmentation was preserved, and gross pathological alterations were lacking. The reduced metabolic capacity of the hepatocyte was apparently compensated for by an increase of total liver mass, resulting in maximum values of all parameters investigated in March. The second phase from March to April was characterized by a decrease of all liver parameters investigated and severe alterations in hepatocellular structure. These observations are interpreted as evidence of drastic structural and functional reorganization in spring. Comparison with data from laboratory fish reveals that part of the wintering phenomena can be attributed to processes of temperature and nutritional adaptation. However, the overall adaptive response observed in golden ide in the outdoor pond profoundly differed from that of fish subjected to selected environmental variables in the laboratory. Since golden ide is in use as a test fish for the assessment of chemical toxicity, the observation of naturally occurring changes in the condition of golden ide may be of relevance with regard to the reproducibility of test results throughout the year. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company