Thousands of piscine specimens, in tall, stoppered glass jars, live in the nine windowless rooms that are his domain. Seen only occasionally by the general public, they lie behind the scenes at the museum, down long corridors lined with files and ledgers, in the depths of the Spirit House wing. Mr Crimmen rules over 4.5km of shelving crowded with sightless, sunken eyes, pale fins and slack jaws, perpetually swimming their final swim, suspended in 70 per cent alcohol.
For two centuries, pickling in alcohol has remained the most efficient way to preserve fish. (The earliest specimens in the collection are kept in ships' rum.) Among the ghostly company are a pair of Serranus Variolosus (aka groupers) caught on Captain Cook's second voyage to the Marquesas Islands in 1774, and a supercilious-looking Plectognathi Gymnoduntes (pufferfish) hooked by Darwin from the deck of the Beagle in the Galapagos Islands in 1835, floating nose-downwards in its slender jar.
Although this may sound a creepy place, a tour with Mr Crimmen is in fact a remarkably cheerful affair. He does not hesitate to throw off his jacket, roll up his sleeves, and haul the most spectacular specimens up from the odorous depths of the large central alcohol tank. "This is the head of a basking shark," he says, bodily yanking out an enormous glassy- eyed lump. "Harrods rang us up; they were selling a basking shark by the slice and asked us if we'd like the head." He lets it fall back into the brown liquid, alongside a "rather rare ray" and the stiff corpse of an enormous carp.
Shelves are labelled in fountain-penned script; one is marked "stomach contents" and another cabinet contains nothing but fish ear bones. When a fish is caught that cannot be identified, the specimens, together with the expertise of the department, will usually provide the answer. But although this vast collection is one of the biggest existing fish archives, it still doesn't hold a specimen of every fish in the world; they number around 24,000 different species. New ones are discovered all the time - Mr Crimmen has seen "thousands" in his 22 years at the museum. "We get visitors from all over the world. There's a global traffic of pickled fish - we send fish off by post for comparison in overseas laboratories. Identification stops here," says Crimmen. "If we can't identify it, either it's new, or nobody can."
Normally, the specimen collections at the museum are not open to the public, but as part of National Science Week (which ends on 22 March), it is possible to visit behind the scenes; tours are free on production of a valid Museum ticket. Behind-the-scenes tours of the fish and other museum archives are regularly arranged for Members of the Natural History Museum; Independent on Sunday readers can become members at a 15 per cent discount during National Science Week on production of this newspaper (normal rates: pounds 25 individual; pounds 12 child or OAP; family pounds 42).
! Natural History Museum enquiries: 0171 938 9123