This funky-looking snake is the Tentacled Snake

To answer your question, the tentacles are little sensory organs. They hunt fish underwater, so maybe they help? They have a better tool than those tentacles for hunting fish, though, and it's behavioral.

For context, fish have a few extremely quick "starts" that are deeply embedded instinctive responses to threats. They happen quicker than a larger animal can really even think, and they start with a specific bend of the body. The most studied (and the most common I think?) is the "C-start", so named because it involves the fish bending its body into a C-shape away from a threat before they start swimming away.

Snakes have quick predatory reflexes, but a fish small enough for them to eat will be quicker. To overcome this fact, tentacled snakes have an incredibly simple and elegant trick.

To put it simply, the snake "herds" the fish into its mouth. It will slide in alongside the fish out of striking range, and suddenly flick a few vertebrae down the length of its body, on the opposite side of the fish from where the snake's head is. When the fish then instinctively "c-starts" away from the movement, it flees directly into the snake's waiting mouth.

Yes, this snake abuses the fish's aggro mechanics for maximum farm efficiency