Water and ion balance in hydrating oocytes of the grey mullet, Mugil cephalus (L.), during hormone‐induced final maturation

Abstract

Sequential changes in water content and inorganic ion concentrations occurring in intra-ovarian oocytes of the grey mullet, Mugil cephalus L., during hormone-induced final maturation are described. Post-vitellogenic oocytes have a water content of 59.4%. During final maturation, oocyte water increases rapidly to a maximum of 84.8% at oviposition. Hydration is accompanied by a relatively small increase in dry matter due to the concurrent uptake of inorganic ions and an apparent uptake of organic matter.Net uptake of Ca" during hydration is negligible. Net uptake of Mg2+ and Na' occurs in less than equimolar proportions. Net uptake of K + and CI-occurs in greater than equimolar proportions prior to ovulation, returning to equimolarity at oviposition. Hence, hydration results in a dilution of intracellular Ca2+, Mg2+ and Na+ to minimum concentrations at oviposition. In contrast, K + and CI-concentrations are slightly elevated prior to ovulation, returning to initial levels at oviposition. A I:I stoichiometric relationship in net uptake of K + and CI-is evident. Intracellular osmotic pressure in post-vitellogenic oocytes is 203.4+ 18.0 mOsmol kg-I .Osmotic pressure rises to a peak of 421.3 + 17.3 mOsmol kg-I prior to ovulation, then declines to 313.3k 15.0 mOsmol kg-I at oviposition. This rise in osmotic pressure prior to ovulation cannot be accounted for solely on the basis of inorganic ion uptake and must be attributed to changes in intracellular concentrations of organic solutes as well. An apparent increase in nonash dry matter during hydration suggests that a net uptake of organic solute is involved. A relatively small organic molecule with high osmotic activity (e.g., amino acids) is implicated.

Hydration of rainbow trout oocyte during meiotic maturation andin vitroregulation by 17,20β-dihydroxy-4-pregnen-3-one and cortisol

“…This suggests that an uptake of organic matter still occurs, at least until ovulation, in the rainbow trout oocyte. A dry mass increase during in vivo hormone-induced maturation was also reported in grey mullet, Mugil cephalus, and was linked to an uptake of small organic molecules with high osmotic activity (Watanabe and Kuo, 1986). An uptake of proteins has also been shown during in vitro oocyte maturation in Fundulus heteroclitus (Selman and Wallace, 1983).…”

Hydration of rainbow trout oocyte during meiotic maturation andin vitroregulation by 17,20β-dihydroxy-4-pregnen-3-one and cortisol

“…This suggests that an uptake of organic matter still occurs, at least until ovulation, in the rainbow trout oocyte. A dry mass increase during in vivo hormone-induced maturation was also reported in grey mullet, Mugil cephalus, and was linked to an uptake of small organic molecules with high osmotic activity (Watanabe and Kuo, 1986). An uptake of proteins has also been shown during in vitro oocyte maturation in Fundulus heteroclitus (Selman and Wallace, 1983).…”

Evidence for a role of Na+,K+‐ATPase in the hydration of Atlantic croaker and spotted seatrout oocytes during final maturation

“…Similarly, it was concluded from earlier studies with mullet and plaice oocytes that hydration is the result of changes in both inorganic ions and organic compounds (Craik and Harvey, '87;Watanabe and Kuo, 1986). The induction of both hydration mechanisms appears to be dependent upon K + influx into croaker oocytes or ovarian follicle somatic cells, since no hydration occurred when the ion was omitted from the external medium.…”

“…A proportionally greater increase in K + compared to Na+ content has also been observed during hydration in the oocytes of other marine pelagic-spawning species (pelagophils), mullet (Mugil cephalus), cod (Gadus morhua), and plaice (Pleuronectes platessa) (Watanabe and Kuo, 1986;Craik and Harvey, 1987). In marked contrast, the moderate hydration observed in the oocytes of a freshwater fish, the ayu (Plecoglossus altiuelis), was accompanied by an increase in Na+, but not K+ content (Hirose and Ishida, 1974).…”

Effect of a low water concentration in chloride, sodium and potassium on oocyte maturation, oocyte hydration, ovulation and egg quality in rainbow trout

“…Together these results indicate that oocyte hydration is impaired during FOM occurring in low salinity water. Oocyte hydration has been described for several species (Finn et al, 2002;LaFleur and Thomas, 1991;Milla et al, 2006;Watanabe and Kuo, 1986). Liberation of free amino acids and an uptake of inorganic ions occur during maturation.…”

“…Oocyte hydration has been described for several species (Finn et al, 2002; LaFleur and Thomas, 1991; Milla et al, 2006; Watanabe and Kuo, 1986). Liberation of free amino acids and an uptake of inorganic ions occur during maturation.…”

Hydration of rainbow trout oocyte during meiotic maturation andin vitroregulation by 17,20β-dihydroxy-4-pregnen-3-one and cortisol

“…This suggests that an uptake of organic matter still occurs, at least until ovulation, in the rainbow trout oocyte. A dry mass increase during in vivo hormone-induced maturation was also reported in grey mullet, Mugil cephalus, and was linked to an uptake of small organic molecules with high osmotic activity (Watanabe and Kuo, 1986). An uptake of proteins has also been shown during in vitro oocyte maturation in Fundulus heteroclitus (Selman and Wallace, 1983).…”

Evidence for a role of Na+,K+‐ATPase in the hydration of Atlantic croaker and spotted seatrout oocytes during final maturation

“…Similarly, it was concluded from earlier studies with mullet and plaice oocytes that hydration is the result of changes in both inorganic ions and organic compounds (Craik and Harvey, '87;Watanabe and Kuo, 1986). The induction of both hydration mechanisms appears to be dependent upon K + influx into croaker oocytes or ovarian follicle somatic cells, since no hydration occurred when the ion was omitted from the external medium.…”

“…A proportionally greater increase in K + compared to Na+ content has also been observed during hydration in the oocytes of other marine pelagic-spawning species (pelagophils), mullet (Mugil cephalus), cod (Gadus morhua), and plaice (Pleuronectes platessa) (Watanabe and Kuo, 1986;Craik and Harvey, 1987). In marked contrast, the moderate hydration observed in the oocytes of a freshwater fish, the ayu (Plecoglossus altiuelis), was accompanied by an increase in Na+, but not K+ content (Hirose and Ishida, 1974).…”

Effect of a low water concentration in chloride, sodium and potassium on oocyte maturation, oocyte hydration, ovulation and egg quality in rainbow trout

“…Together these results indicate that oocyte hydration is impaired during FOM occurring in low salinity water. Oocyte hydration has been described for several species (Finn et al, 2002;LaFleur and Thomas, 1991;Milla et al, 2006;Watanabe and Kuo, 1986). Liberation of free amino acids and an uptake of inorganic ions occur during maturation.…”

“…Oocyte hydration has been described for several species (Finn et al, 2002; LaFleur and Thomas, 1991; Milla et al, 2006; Watanabe and Kuo, 1986). Liberation of free amino acids and an uptake of inorganic ions occur during maturation.…”

Hydration of rainbow trout oocyte during meiotic maturation andin vitroregulation by 17,20β-dihydroxy-4-pregnen-3-one and cortisol

“…This suggests that an uptake of organic matter still occurs, at least until ovulation, in the rainbow trout oocyte. A dry mass increase during in vivo hormone-induced maturation was also reported in grey mullet, Mugil cephalus, and was linked to an uptake of small organic molecules with high osmotic activity (Watanabe and Kuo, 1986). An uptake of proteins has also been shown during in vitro oocyte maturation in Fundulus heteroclitus (Selman and Wallace, 1983).…”

Evidence for a role of Na+,K+‐ATPase in the hydration of Atlantic croaker and spotted seatrout oocytes during final maturation

“…Similarly, it was concluded from earlier studies with mullet and plaice oocytes that hydration is the result of changes in both inorganic ions and organic compounds (Craik and Harvey, '87;Watanabe and Kuo, 1986). The induction of both hydration mechanisms appears to be dependent upon K + influx into croaker oocytes or ovarian follicle somatic cells, since no hydration occurred when the ion was omitted from the external medium.…”

“…A proportionally greater increase in K + compared to Na+ content has also been observed during hydration in the oocytes of other marine pelagic-spawning species (pelagophils), mullet (Mugil cephalus), cod (Gadus morhua), and plaice (Pleuronectes platessa) (Watanabe and Kuo, 1986;Craik and Harvey, 1987). In marked contrast, the moderate hydration observed in the oocytes of a freshwater fish, the ayu (Plecoglossus altiuelis), was accompanied by an increase in Na+, but not K+ content (Hirose and Ishida, 1974).…”

Effect of a low water concentration in chloride, sodium and potassium on oocyte maturation, oocyte hydration, ovulation and egg quality in rainbow trout

“…Together these results indicate that oocyte hydration is impaired during FOM occurring in low salinity water. Oocyte hydration has been described for several species (Finn et al, 2002;LaFleur and Thomas, 1991;Milla et al, 2006;Watanabe and Kuo, 1986). Liberation of free amino acids and an uptake of inorganic ions occur during maturation.…”

“…Oocyte hydration has been described for several species (Finn et al, 2002; LaFleur and Thomas, 1991; Milla et al, 2006; Watanabe and Kuo, 1986). Liberation of free amino acids and an uptake of inorganic ions occur during maturation.…”