Can rats eat melon?

Yes, but only a little: rats can eat melon. Melon appears on the PDSA’s chart of safe fruit and veg for rats. Woodgreen lists it as a treat, the University of Minnesota includes it among foods you can offer, and the Swiss animal welfare society (STS) counts melons as suitable fruit. The Zurich animal welfare society (Zürcher Tierschutz) lists melon as an occasional food. None of the sources mentions watermelon specifically.

How to serve it: peeled, a small piece

Good to know: The PDSA’s chart says to give fruit only in very small amounts as a treat, since it is high in sugar, though its page suggests small amounts of fresh fruit and vegetables daily. RSPCA Australia lists fruit as a treat to give infrequently and in small amounts, the Merck Veterinary Manual says limited amounts, and the Zurich animal welfare society (Zürcher Tierschutz) says occasionally. The Swiss animal welfare society (STS), on the other hand, counts fruit as daily fresh food, the University of Liverpool’s veterinary practice mentions small daily amounts, and the Royal Veterinary College suggests some fruit daily, so we err on the side of caution.