The North American ethologist Jonathan Balcombe is well-known to a broader public by his bestseller ‚Pleasurable Kingdom‘. His latest book ‚What a Fish Knows‘ published in 2016 does not take second place. On 250 pages the author comes across all kinds of fish species and shows us the unbelievable diversity of abilities to see, hear, smell, and sense, to the point of amazing cognitive performances of our ‚underwater-cousins‘.