Hormonal changes over the spawning cycle in the female three-spined stickleback, Gasterosteus aculeatus

Ovarian weights peaked in “ready to spawn” females, dropped after spawning, before again progressively increasing from 6 to 72 hps. Plasma T levels showed peaks at 24 and 48 hps and decreased at 72 hps, while E2 levels increased already at 6 hps and remained at high levels up to 48 hps. There was a strong positive correlation between T and E2 levels over the spawning cycle. Pituitary lh-β mRNA levels showed a peak at 48 hps, while fsh-β did not change. The neuropeptides and gpr54 did not show any changes. The changes in T and E2 over the stickleback spawning cycle were largely consistent with those found in other multiple-spawning fishes whereas the marked correlation between T and E2 does not support T having other major roles over the cycle than being a precursor for E2.