Underwater Amazon

Jeremy Wade explains why Manaus fishmarket is an ‘accidental temple to biodiversity’

In the geographical centre of the Amazon stands an ornate structure of wrought iron, fabricated in Europe a century ago and reputedly designed by Eiffel. Inside, early each morning, down either side of a long hallway, crowds of people inspect weird and wonderful creatures which, although abundant in Amazonia, are not normally seen outside this building.

We are in the fish market at Manaus, accidental temple to biodiversity, and as such well worth a non-shopping visit - where the peculiar forms and lifestyles of the species on view give a graphic insight into the nature of the Amazonian ecosystem.

Take the bulky black-and-green fish looking rather like our European carp - until you notice the crushing plates set in muscle-packed jaws. Much prized for its firm, tasty flesh, the tambaqui feeds almost exclusively on the seeds of trees that, half the time, are nowhere near water. It pulls off this unlikely feat thanks to an unlikely feature of Amazon geography: the annual flooding of huge areas of forest - to a depth of ten metres or more. So abundant is this seasonal feast that during the rest of the year, when it is confined to the river channels, the tambaqui lives on its fat reserves. Fish bought from the market between August and December will have empty stomachs.

Another species on view that makes the most of this season ticket into the forest is the aruanã and again the clues are in its design: a long body with a paddle-like tail for propulsion, ruler-straight back for a stealthy approach just below the surface, big eyes set high on the head, and a huge lower jaw that opens like a drawbridge. Also known as the ‘water monkey’, the aruanã specialises in surface-to-air attacks on insects minding their own business up trees. It can grab prey from branches a metre above the water. Most aruanã are caught in nets, but any spotted with puncture wounds will have been shot by sharp-eyed bow-fishermen.

There are also fish here that exploit the less obvious opportunities provided by low water. Laid out on a slab in a corner are huge fillets looking like two-metre-long kippers. This is the meat of the pirarucu, one of the world’s largest freshwater fish, sometimes weighing as much as 150 kilos (3OOlb). When the water level falls, in the Amazonian ‘summer’, some backwater lakes become very shallow and deoxygenated, and the fish in them become torpid. But not this giant predator. It is able to absorb oxygen from air gulped at the surface, and so remains active while the smaller fish it feeds on are sluggish and vulnerable.

Unfortunately for the pirarucu, however, its habit of periodically surfacing, then burping a trail of bubbles, makes it vulnerable to fishermen, who hunt it with thick-cord nets and harpoons. Add to this the market’s (unaccountable) taste for salted, as opposed to fresh, pirarucu, and the result has been a wholesale onslaught. In recent years numbers have declined to the point where it is a protected species. But for many riverside dwellers, selling salted pirarucu meat is one of very few ways to earn some cash, so they still find their way to market.

In fact, such is the city’s demand for food - a million-plus inhabitants and growing - that many of the fish on view will have come, packed in ice, from tributaries and lakes a week’s journey, or more, away by boat. Manaus has become the centre of a food web that reaches right into the region’s furthest extremities. Despite the Amazon’s vastness, therefore, harvesting fish stocks sustainably is becoming a matter of some urgency - not just for humans but also those others with a vested gastronomic interest: dolphins, caimans, otters, many species of birds, the odd jaguar...

And not just predators. Scavengers also have a stake. Looking once more round the market hall - at the bright colours, striking patterns, armour-plated bodies, tentacles, teeth - we are suddenly aware of an absence. The Amazon’s most famous fish is not here. This is nothing to do with declining stocks, however. Although good eating, if somewhat bony, the piranha is not really a commercial species: normally it is eaten only by the riverside dwellers.

The most interesting way to see piranhas is to catch your own. Pay a visit to a backwater lake when the water is low and the fish are concentrated. No special tackle is needed: Just a short piece of line, a hook, and some cut fish or meat. A cane pole is an optional extra. To stop fish severing the line, local people make their own long-shanked hooks from 5-8cm (2-3in) of stiff wire bent at one end.

Unhooking requires careful handling and concentration - their dentition really is formidable. Despite the tales, however, they are not normally a threat to swimmers - although there are rare ‘hungry’ lakes around, and anybody with a bleeding cut shouldn’t swim anywhere.

A more exciting method of rod-and-line fishing is casting artificial lures that mimic small fish. This can tempt red-bellied piranhas weighing close to a kilo (2lbs) and black piranhas potentially twice that size. Often other predators get in on the act, too: notably tucunaré. (the ‘peacock bass’), toothy traíra, and sometimes aruanã. Lumps of fish offered on the riverbed will pick up bottom-feeding catfish such as the red-tailed pirarara or the zebra-striped surubim - if a stingray doesn’t get there first (a fish that poses a much more real threat to paddlers than piranha). There’s even a chance, hard to believe 1500km (900 miles) from the sea, of a shark snaffling the bait. Local fishermen still take them, and sawfish, very occasionally on their catfish-lines - moth-eaten stuffed specimens can be seen hanging in the Casa Dragão fishing-tackle shop near the market.

Even without sharks, though, visitors to Amazonia have the opportunity to marvel at more fish species in a couple of days than during a lifetime in Britain - perhaps dozens (from a total of some 3,000) of different variations on the fish theme, some of them hard to believe. Biodiversity ceases to be just a word, a dry and distant academic concept. In the Amazon’s fish it can be spectacularly seen.

Jeremy Wade is a freelance writer who has covered aspects of Amazonia for the Sunday Telegraph and BBC Wildlife magazine.