From Guardian:
Scientists have been wary of discussing the pleasures experienced by animals, seeing nature as a brutal struggle for survival. But as the similarities in physiology and biochemistry between humans and animals become ever clearer it becomes harder to ignore the joy of life in the wild. Animal behaviour scientist Jonathan Balcombe takes us on a tour of the sunny side of animal life, and argues that a shared capacity for feeling demands a radical shift in our relationship with the animal world.
Six-barred angelfish
“One of nature's many mutualisms is demonstrated by cleaner fishes which pluck parasites and nibble algae and loose skin from client fishes. These relationships, built on trust and cemented by the rewards of touch and nourishment, have been well studied, but I've yet to see any specific mention of the word pleasure in any of the papers I've read. Here a team of two cleaner wrasses provide spa treatment to an angelfish. It's clearly in the angelfish's interests to get rid of parasites, but there's mounting evidence for a more immediate, complementary benefit for this behaviour: the tactile ministrations of the cleaner wrasses feel good”
More here.