Rachel Roddy's Recipe for Lemon Herb Crab Linguine

The fish auction starts at 4 p.m. Around 30 shoppers from restaurants, shops and markets sit on one side of the large, cool room that smells of the rock pool. A conveyor belt separates the buyers from the operation of the room: two auctioneers and four men move hundreds of polystyrene boxes containing thousands of creatures. Fish that, minutes earlier, had been unloaded from the boats we watched return from the sea and dock in the channel that crosses Fiumicino.

If you landed at Fiumicino airport, just outside Rome, you may have seen the canal as the plane curves in to land on a runway near the coast. It was built under Emperor Claudius in 46 AD, part of Portus, a large artificial harbor for a growing city backed by an empire. Built to complement Ostia, Ancient Rome's original mouth to the sea, Portus would eventually supplant it and for 500 years provide a vital conduit and powerful port. While Fiumicino's new name appears on maps dated 1582, urban and port redevelopment took place in the early 1800s and streets were named with a purpose: Via del Tonno (tuna ), Via dei Merluzzi (cod), Via dei Salmoni (salmon), Via delle Ostriche (oysters). Today, 25 trawlers and crew can fish in designated areas, then dock along the old waterway to bring 100 different species to the daily asta that takes place in a side street near the mouth of the canal.

I've been fishing aste before, so I expect to scream. Here, however, it's relatively quiet, save for clicks when shoppers tap a tiny remote device. The boxes of fish are loaded onto the conveyor belt, and also filmed so that their contents appear on a screen; a chain of buying fish for those who sit near the door. An electronic scoreboard details the type of fish, weight, cost, boat and fishing area. Shoppers click and clamor for anchovies, hake, red mullet, red bandfish and even brighter red gurnard, mackerel-like palamita, trevally, ray, cuttlefish, flying squid called totani, octopus, prawns and crabs.

My son is with me talking to a buyer called Maurizio who, between two clicks, tells him the names of the fish, and also secures our future custom by giving Luca what looks like a little shark. Early the next morning, we return to Fiumicino to find Maurizio, who runs one of the last stalls in the covered market. It's a dazzling array of pink, silver and white, scales and shells that reflect the light. There is a momentary moral dilemma; a good thing, I think - a reminder to think twice and ask questions. We taste local prawns and buy clams called telline, and a crab with incredible legs.

As a cook, eater and writer, I find the RSPCA advice to be helpful, clear and sobering. Before cooking, the crabs should be cooled or stunned into a dormant state (torpor) so that they can be humanely killed by poking them with a sharp knife. The Marine Conservation Society's Good Fish Guide recommendations are equally straightforward, a good thing when it comes to food. At this time Shetland brown crabs are a good choice.

A beautiful dish from a beautiful creature, so serve immediately.< p class="dcr-3jlghf">Prepare 10 minCook 10 minServes 4

300g white and brown crab meat, at room temperature 1 untreated lemon 2 tbsp heaped soup of finely chopped parsley A pinch of dried oregano 120ml extra-virgin olive oil 1 small red chilli, finely chopped450g linguine or spaghetti

Bring a large pot of water Bring to the boil, salt, stir, then add the pasta. Start a timer and cook until al dente, which will depend on the brand, but about nine minutes.

While the pasta cooks, stir crab meat, lemon zest and a tablespoon of its juice, herbs, olive oil and chilli in a large hot bowl (it is important that it is hot).

When the pasta is cooked, drain it or use a colander or tongs to lift it out of the bowl and toss gently with the other ingredients. Serve immediately.

The Guardian aims to publish sustainable fish recipes. Check the rankings in your region: United Kingdom;