Yes, pet rats can eat ugli fruit.

Ugli fruit, also known as uniq fruit, is a citrus fruit that is a hybrid of grapefruit, orange, and tangerine. It has a unique flavor and is safe for rats to consume in moderation.

Ugli fruit is a good source of vitamin C and dietary fiber, which can be beneficial for your pet rat’s health. When offering ugli fruit to your rat, provide small pieces or slices. Rats have small stomachs, so a small portion is typically sufficient. Remove any seeds or tough parts before serving.
It’s important to note that while fruits like ugli fruit can be a healthy addition to a rat’s diet, the majority of their food should consist of a balanced rat pellet or block that provides all the necessary nutrients. Fruits should be offered as occasional treats and should not replace their primary food source.
Always wash fruits thoroughly before offering them to your rat. If you have any concerns about your pet rat’s diet or health, consult with a veterinarian who specializes in small animals for specific dietary recommendations and to ensure your pet rat’s overall well-being.
Also explore the compatibility of these foods for your pet rat:
Fish, Peanuts, Coffee,
Further Reading :
https://www.pdsa.org.uk/pet-help-and-advice/looking-after-your-pet/small-pets/your-rat-s-diet
https://www.thesprucepets.com/feeding-pet-rats-1238500
https://vethelpdirect.com/vetblog/2022/10/20/what-makes-a-good-diet-for-a-pet-rat/