My kitten ate tuna and has diarrhea with a swollen bum. Is it serious?

A sudden change in diet can lead to diarrhea, even blood diarrhea. But it can also be caused by a GI illness or intestinal worms among other causes. Feed Boz a bland diet of boiled white meat chicken (no bones) in small amounts several times a day for a couple of days. Then slowly add back in his normal diet. If the diarrhea continues on the bland diet, he starts vomiting food, stops drinking water, starts vomiting water, or becomes very lethargic, he will need to see a vet right away. Best of luck.

My biggest immediate concern would be for intestinal parasites. Most kittens have them, and if she hasn't seen a vet yet and been dewormed, she needs to. She's suffering pretty significant fluid losses for a tiny creature. Make an appointment tomorrow, and bring a stool sample with you, so that the type of parasite can be determined and appropriate treatment started.

He does look very sore and any diarrhoea which lasts more than 2 days in young kittens should be treated as they can rapidly become dehydrated and malnourished if not absorbing food and water sufficiently. I would get a stool sample checked for parasites and also start him on a specialist, highly digestible intestinal diet for 3-5days followed by a good quality kitten food introduced gradually. Probiotics can also be helpful

Poor Jameson. This is pretty common in kittens for many different reasons. It could be stress related from moving to her new home. She also could have some intestinal parasites that is causing the diarrhea. You said you have not changed her food, so I"m assuming she is eating what she was on at the shelter. IF you have changed from that, this could also be causing diarrhea. I worry about her anus bulging. They strain when having diarrhea and this could lead to a rectal prolapse. I think she should see a veterinarian so they can test for intestinal parasites and hopefully get her started on some diarrhea medications and possibly a bland diet. They can also help with dehydration by giving her some fluids under her skin as these little guys can become dehydrated very quickly. Hope this little girl can get turned around soon.

It will go down one the stools become normal, i suspect at the moment he is suffering from diarrhea and this is why the anus looks like that, once the stools become normal again the anus will recover.

Luckily it looks like her anus is just swollen and red causing it to protrude. I don't see any sign of a prolapse thankfully. Try and keep it clean and comfortable until you can get to the vet tomorrow.

Swelling of the anus/rectum could be due to constipation/hard stools, anal gland issues, allergies, irritation, or other problems. You would need to have the area looked at by your vet to determine what is going on and get the appropriate treatment. Be sure to let your vet known of any other issues you may have seen such as changes in appetite, energy levels, stool habits, etc. You can also use an Elizabethan (cone) collar to prevent your cat from licking/chewing at the affected area if it is bothersome until you can get to your vet.