A matter of degree with a real line between them. A kittenfisher is a genuine person using flattering, out-of-date photos — they'll show up. A catfisher has invented an identity, often with someone else's pictures, and typically avoids ever meeting. Impersonation on its own isn't a crime everywhere; what catfishing is usually used for — fraud, extortion — is.
Side by side
Aspect
Catfishing
Kittenfishing
The person
Doesn't exist as shown
Real, just flattered
The photos
Often someone else's
Theirs, older
Will they meet?
Avoids it
Yes
Legally
Often fraud
Rarely criminal in itself
What each one means
Catfishing
Catfishing is creating a fake online persona to deceive someone — most often into a relationship, but also for money, harassment, or simple experiment. The person you're talking to doesn't exist as described, and the photographs usually belong to a real stranger who never consented.
Kittenfishing is presenting a mildly exaggerated, overly flattering version of your real self on a dating profile — old or heavily edited photos, an inflated job title, a couple of added inches of height — without inventing a fully fake identity.