I have two large goldfish that are 10 yrs old and up to now have had no problems. Recently, one of them seems to always have his mouth open. I rang a local fish shop and they told me to look and see if the fish had some gravel in his mouth. Checked and there's nothing there, but he also said it may be lockjaw. What happens if it is lockjaw. The fish is acting normal, eating and very healthy
