Ovarian monosaccharides (glucose and fructose): hormonal effects and their role in final oocyte maturation and egg quality in catfish Heteropneustes fossilis, Bloch.

ABSTRACT

In the catfish H. fossilis, ovarian glucose and fructose levels showed significant annual variations that could be correlated with the gonado-somatic index. The concentration of the sugars, which was low in resting phase of gonad increased with the onset of oogenesis, reaching the peak in prespawning (June) phase. Glucose is the predominant monosaccharide in the late oogenesis, while fructose in early oogenesis and resting phase. Administration of a single injection of HCG (100 IU/fish) decreased glucose at 4 hr but increased fructose (6 hr) in the resting phase. In the preparatory phase (active oogenesis), fructose decreased significantly at 4 hr and glucose at 6 and 12 hr. In the prespawning phase, HCG administration induced a significant decrease in glucose level at 2 hr but increased it significantly at 16 and 18 hr. Fructose concentration, on the other hand, decreased > or = 4 hr. The involvement of different energy substrates (glucose, fructose, 2-deoxyglucose and pyruvate) on final oocyte maturation and viability of eggs were demonstrated in an in vitro study, employing incubation of mature oocytes in medium containing one or the other energy substrates. Glucose at 4 and 8 mM concentrations increased the viability of eggs without affecting germinal vesicle break down (GVBD) and at high concentrations (16 and 32 mM) marginally increased GVBD but decreased viability. Pyruvate at high concentrations (> or = 8 mM) produced a positive effect on both GVBD and viability. Fructose and 2-deoxyglucose did not elicit any effect on these parameters. The results suggest that glucose has an active role in catfish oogenesis and maintaining egg quality and HCG influences monosaccharide metabolism in a season-dependent manner.