Hello there. My name isXXXXX and it sounds possible that he got into something that has caused an allergic reaction in his mouth. That is great that you rinsed out his mouth you want to make sure whatever caused the issue is no longer in his mouth. You can also give him benadryl. This will help reduce the reaction and calm down the irritation and inflammation. The dose is 1 mg per pound every 8 hours. This is a higher dose than in humans so it may seem like a lot but they require more. So i would dose him now, repeat in 8 hours. I would have him seen in the morning if his mouth is not back to normal or call and have him seen tonight if anything worsens. But the benadryl should definitely help. I would also check the yard and the house to make sure that he didn't get into anything else that could have caused this reaction. If not then I would hesitate to give him salmon in the future. I hope this helps and makes sense. Please do not hesitate if you have any further questions or concerns. I would be happy to help. Please do not forget to rate my response so I receive credit for my time. Thank you!