As director of animal sentience at the Humane Society Institute for Science and Policy, ethologist Jonathan Balcombe is someone I am unlikely to meet propping up the bar at the Flyfishers’ Club, leafing through a copy of Field & Stream. The subtitle to his latest book had me dreading a farrago of namby-Bambi, squirrel-kissing sentimentality, but I was mistaken: it is as cogent, salutary and substantial a study of piscine behaviour as I have read in years.

Balcombe and I love fish in different ways. As an angler of some commitment, I have spent fifty-odd years devising stratagems for their downfall, whereas he is convinced they are ‘individuals with minds and memories’. He does not think I should be hooking them in the jaw, and is profoundly concerned at the number of them killed by humans every year (estimated to be up to 2.7 trillion worldwide). He contends that fish feel pain, and to some extent I concur – they possess a dopamine system and, as this book proves, some can even get hooked on amphetamines, though that is not in the traditional repertoire of angling baits.

Wearing its learning lightly, What a Fish Knows is impressively rooted in science, some of it fairly recherché. The author’s own field notes range from Grandma, an elderly Caribbean reef shark, to the behaviour of garibaldis in his local Asian takeaway, and embrace such diverse specimens as the orange roughy and the unfortunately named slippery dick (Halichoeres bivittatus). The aim is to explore the sensory world (or Umwelt) of the subaqueous zone and to dispel myths about fish that continue to prevent us from appreciating how they should be treated. Along the way he describes various experiments on fish that have been carried out at different times: Karl von Frisch surgically blinded his pet catfish Xaverl; Norwegian vets have attached foil heaters to goldfish. Although he raises an eyebrow at some of these practices, he argues that our understanding of the complexity of the world’s 33,000 fish species has been beneficially enhanced by them.

This is a book full of wonders. Koi carp, it seems, can distinguish between the blues of Muddy Waters and the music of Schubert. Sockeye salmon detect one part of shrimp extract diluted in a hundred million parts of water. Male anglerfish have the largest nostrils relative to head size of any animal (this helps them to avoid, in the darkling depths, mating with the wrong anglerfish – there are 162 known species). The African elephantfish uses a form of electrical echolocation that detects time differences of pulses down to a millionth of a second. The orange-dotted tuskfish is a tool user capable of smashing clams against rocks; certain Limpopo tigerfish have learned to snatch swallows flying overhead at twenty miles per hour; the admirable archerfish – with the aplomb of some belted earl swivelling in his grouse butt – rotates its body while shooting water at passing insects, simultaneously compensating for ‘the optical distortion produced by the water-to-air transition’. Who knew what a fish knows?

One of the more intriguing sections concerns sex. Various species display parthenogenesis, sequential hermaphrodism and a penchant for oral sex (the female armoured catfish drinks sperm and passes it through her digestive tract for fertilisation in four seconds flat). The clownfish changes sex (that didn’t feature in Finding Nemo), the Japanese pufferfish woos his ladylove with sculptures in the sand, the female brown trout fakes orgasms (I shall have to watch out for that on my beat of the Itchen) and the Mauritian spotted mophead indulges in S&M. All right, I made up that last one, but there genuinely is a male Thai priapium that has his copulatory organ beneath his throat (plus ‘a fully functional testicle’) and the member (or gonopodium) of the otherwise humble mosquitofish can extend to 70 per cent of his body length.

As an eight-year-old, our author wrote a report for school about salmon mating: ‘you would think they are fighting but actually they are thoughrally injoing it’. Exactly.

As well as being agreeably prinked with good humour, this book generally eschews anthropomorphism and special pleading, though just occasionally we seem to be veering into ‘Cats Are People Too’ territory. I remained unmoved by the anecdote about how Seabiscuit, a goldfish, tried to rescue his companion, Blackie (who ‘died in June 2015, age six, apparently due to a faulty filter’). I am also unconvinced by divers ‘befriending’ individual fish – I have ‘petted’ wild stingrays in Tahiti and Seychellois bonefish, and it’s nothing more than cupboard love. Try it out on Barry the Bad ’Cuda and see how long the relationship lasts. The most hilarious tale concerns an Alaskan scientist on her Jamaican honeymoon whose husband becomes amorously excited while swimming, arousing the voyeuristic instincts of a host of angelfish.

Balcombe’s serious point is that factory ships, bottom trawling, by-catch dumping and ghost nets are ruinously depleting our stocks of fish. It’s a gloomy finale to the book, just as I was thoughrally injoing it.