Changes in tissue ion contents and ultrastructure of food-deprived immature American eels, Anguilla rostrata (LeSueur)

Abstract

The fasting-induced ultrastructural and ionic changes which occur in American eel (Anguilla rostrata) tissues were studied following 6 (fasted) and 12 (starved) months of food deprivation. Muscle and liver Na+ and Ca2+ ion contents generally rose at the expense of plasma ion concentrations; K+ levels changed little. The fiber area (size) of red (RM) and white (WM) muscles declined with the length of the fast. However, the relative proportion of RM myofibrils actually increased suggesting that red fiber performance was maintained during the fasting period. WM performance probably drops significantly as a result of a decreased fiber size and the relative volume of myofibrils present. Liver morphometric changes became apparent only after 12 months of food deprivation, although a significant increase was noted in the volume of the cell occupied by endoplasmic reticulum at 6 months. These studies indicate that tissue ultrastructural changes occurred with food deprivation in eels and that these were consistent with previously observed alterations in tissue protein and enzyme activities. It is proposed that these modifications are associated with the mobilization of tissue metabolic reserves, and not necessarily a dramatic metabolic reorganization of American eel tissues during food deprivation.