If you're asked to picture a creature having the time of its life, a fish probably isn't the first animal that comes to mind. But new research is challenging that perception.
The results, said Soares, are a step towards considering fish to be closer to other, "normal" vertebrates like cats and dogs. Soares studies mutualisms, or interactions between species that benefit both parties. In coral reefs, she says, one of the most fascinating examples is between the bluestreak cleaner wrasse, a sleek silver fish with a bold black stripe, and the threadfin butterflyfish, a yellow-and-white species with striking black markings.Since the study's publication, some scientists have questioned whether the findings are indeed evidence of fish experiencing pleasure. "Can we unequivocally say that this is pleasure in fish? I'm not sure that I would say it in those words.Having said that, it's very difficult to measure pleasure in animals, period, let alone fish," Susana Peciña, a biopsychologist at the University of Michigan-Dearborn who wasn't involved in the study, told NPR. Soares isn't surprised by the caution. She says human observers can more readily ascribe emotions like pleasure to mammals, like dogs or primates.They injected the butterflyfish with a low dose of an opioid mimic, a morphine-like drug that stimulates pleasure receptors. The fish's attraction to the cleaning area increased, says Soares.
