Fertilized steelhead eggs were water-hardened at constant pH levels of 4.0, 4.5, 4.7, 4.9, 5.1, 5.5, 6.0, 6.5, and 7.2. Water uptake was significantly inhibited (P < 0.05) at pH 5.5 and lower. The ability of eggs to resist deformation when subjected to mechanical loads was significantly reduced at pH 6.0 and lower. Eggs transferred to pH 7.2 after water-hardening at pH 4.0, 4.5, or 4.7 gained additional water but the total amount imbibed remained significantly less than that expected for constant exposure to pH 7.2. In contrast, resistance to deformation rose to values typical of continuous exposure to pH 7.2. Eggs transferred to pH 4.0, 4.5, or 4.7 after water-hardening at pH 7.2 lost small but significant amounts of water. Resistance to deformation declined more sharply to values only slightly greater than those expected for continuous acid exposure. Reductions in water content associated with initial water-hardening were irreversible. However, back-transfers indicated that pH-induced changes in water content and resistance to deformation were fully reversible once hardening was completed. Analysis of results suggests that low pH interferes with cortical vesicle exocytosis, affects the osmotic activity of perivitelline colloids, and reduces capsule strength.