Investigations on the
metabolism of viable and nonviable gilthead sea bream (Sparus aurata)
eggs
F.
Lahnsteiner, P. Patarnello-2003
Aquaculture, 223(1-4): 159-174
Abstract:
The present study investigated selected biochemical
parameters in viable and nonviable eggs of the gilthead sea bream, Sparus
aurata. During embryogenesis, S. aurata eggs had a balanced and
stable energy metabolism as the levels of adenosine nucleotides and
acetyl-CoA, and the adenylate energy charge (EC), remained constant. Mg2+-dependent
ATPase, which is involved in membrane-driven ion transport during oxidative
phosphorylation, increased in activity. In nonviable eggs, the levels of
ATP, acetyl-CoA, the adenylate energy charge, and the activities of malate
dehydrogenase were significantly decreased in comparison to viable eggs.
Viable eggs had high Na+/K+-ATPase
activity which remained constant during embryogenesis while Ca2+-ATPase
activity increased. These enzymes were similarly high in nonviable eggs
indicating that the ability for ion transport and for osmoregulation did not
differ. However, nonviable eggs contained nonphysiological high levels of
magnesium and calcium ions indicating ion influx from the seawater. As the
phospholipid levels were significantly lower in nonviable eggs, this ion
influx is thought to be related to changed composition of the oolemma.
Activities of glucose-6-phosphate dehydrogenase,
transaldolase, phosphofructokinase, and pyruvate kinase were constant in
viable eggs of S. aurata during embryogenesis. Pyruvate carboxylase
increased in activity in the embryonic stage. The occurrence of these
enzymes indicated the presence of the enzymatic system for glycolysis for
gluconeogenesis and for the pentose phosphate pathway. The monosaccharide
levels (i.e. total amount, glucose, fructose, galactose) increased steadily
during egg development. Monosaccharides are necessary for nucleic acid
synthesis levels, which increased during embryogenesis, and may also play a
role as osmotically active compounds. In nonviable eggs, levels of all
assayed sugars as well as activities of pyruvate carboxylase and
transaldolase were very significantly decreased.
Enzymes involved in the catabolism of proteins and
amino acids (proteases, aspartate aminotransferase, glutamate dehydrogenase)
were constant in the viable eggs with the exception of aspartate
aminotransferase, which increased significantly in the embryonic stage.
Nonviable eggs had lower activities of glutamate dehydrogenase than viable
eggs, while the other enzyme activities were similar. Amino acid levels and
inorganic phosphate levels were lower in nonviable than in viable eggs.