Hyper-realistic 4K video animation, fixed low-angle camera looking up through the aquarium glass. Two chubby cats (fluffy gray tabby and black-and-white tuxedo) float calmly underwater like adorable pufferfish, with huge spherical bodies, no legs—replaced by delicate translucent fish fins (pectoral front fins, dorsal and flowing caudal tail fins matching their fur colors and patterns). They slowly start to "swim" playfully: fins gently waving and fluttering, tails undulating smoothly, whiskers twitching, eyes blinking, small bubbles rising faster as they move closer together, nudge each other softly, then drift apart again. Water ripples softly on the surface, plants sway lightly, light caustics dance across their fur-fin blend, gravel shifts subtly. Soft ambient bubble sounds, gentle water movement. High detail on underwater fur-to-fin transition, fin translucency and motion, bubble trails, plant sway, and lighting refraction. Professional VFX style for cute, surreal, heartwarming "cats as fish" fantasy