My cat has licked almost all the fur off of her belly and down between her inner back legs, also small patches on her arms. Could she be doing this because I have completely cut fish out of her diet? My other cat is allergic to fish, which is why I have taken fish out.
Yes, I agree with Keshlam in that cat allergies to food are common. Now, your other cat may have an allergy to the new food, and you may have to keep trying foods until you find one that satisfies both cats.
FOOD ALLERGIES: The thing that is difficult about cat food allergies is that you have to find a food with a main ingredient they've never eaten before. If you have the money, you can get cat food from your vet that has duck, lamb, etc. Usually, cats have not had these types of ingredients in over-the-counter foods. Your vet can really help in this area.
OCD / ANXIETY: However, another reason for this behavior in your kitty could be purely change. Cats are habitual creatures. When something changes, occasionally a cat can start, what we would call, an OCD behavior. This is what happened to one of my cats when I boarded him for the first time. I was young and didn't know any better. Plus, pet sitters weren't as prevalent. I left for a week on business to come back to my kitty who chewed the hair off his legs and stomach, similar to your situation. It became such a habit (or maybe some sort of calming technique?) that the OCD lessened through the years but never truly went away. Of course, I never boarded him again.
CHANGES: Have you made any other changes that would affect your cat besides the food change? --- Moving, working later, new person in your life, even moving furniture around. Cats are very sensitive to any type of change. If you can't think of anything, it is probably the food. Now, the hard part is determining whether it's the change itself or an actual food allergy. You will need your vet's help to isolate the true cause.
DISTRACTION AND LOTS OF LOVE: In the mean time, you can try distracting your cat with a toy, like a feather wand, when you see him chew himself. Lots of attention to let her know everything is ok always helps, too.
Best wishes to you and your kitty!
There may be a connection. Some cats do have allergies, though actually an allergy to fish is not uncommon, as you've found. I'd suggest trying another food, looking at ingredients to try to isolate specific items.
Good luck. I hope it isn't an allergy to turkey; as a friend found out, turkey is a common protein source in many cat foods even if it isn't the featured flavor.
There is a medical or psychological problem here. Licking is often a sign that your cat has itchy skin. Ringworm is common in cats and can cause excessive itching. Bacterial infections will also cause severe itching. Allergies, which can be caused by food, will irritate the skin in cats. Dry skin will do the same thing. Cats will also over groom themselves when they are suffering anxiety. Changes in a cat's environment will often cause anxiety. New pets in the home will cause a cat to experience anxiety. Indoor cats, who often aren't given adequate stimulation, will often develop psychological problems.