Energy metabolism in fish development [Oogenesis]

SYNOPSIS. During oogenesis the fish oocytes accumulate several substances of which lipids and glycogen are the major energy substrates. Oocyte maturation is accompanied by an increase in all the enzymes of carbohydrate metabolism. After fertilization, respiration and glycogenolysis are increased and the energy charge is decreased. During early embryogenesis glycogen appears to be the only substrate of glycolysis. Glycolysis and the citric acid cycle are the main sources of energy for the biosynthetic activities and for the maintenance of embryo morphology. There are two patterns of ontogeny of glycolytic enzymes in trout embryos. One group of enzymes does not undergo appreciable changes whereas enzymes within the second group exhibit variable activities. Marked changes in enzyme activity occur during fertilization and gastrulation. Lactate dehydrogenase (LDH) is of particular interest. Its activity increases during gastrulation. This increase in LDH activity is followed by a change in the isozyme pattern and in the adenylate charge. 1mmunochemical and histochemical localization of LDH revealed that its cellular distribution depends on the position of the cells in the embryo. Moving cells had higher levels of LDH activity. The lactate dehydrogenase isozymes appear to play an important role in the regulation of energy metabolism during fish embryogenesis. These gene products are useful biochemical markers of cellular differentiation and organogenesis.