Spaghetti with cockles and three-cornered garlic © Jason Lowe

"Save the cod" has become a motto of our times, and most of us are conscious that cod is a problem species. But what about all the other fish in the sea? It's true that you can Google the MSC (Marine Stewardship Council) or the MCS (Marine Conservation Society) to find out what fish to buy, but it can be confusing.

For me, one answer to the problem is to buy Hugh Fearnley-Whittingstall's new book, The River Cottage Fish Book. It's a big doorstop of a book and a great authority on a subject that we have all been ignoring for decades. Hugh has covered just about every species we have in the UK, informing us about MCS rating, minimum sizes (useful for us fishermen) and when to avoid eating during spawning seasons, etc. The book has some great, simple recipes using the lesser-known species that we don't normally see on the fishmonger's slab. Now that is obviously a problem because if the fishmonger isn't selling species such as grey mullet, gurnard and pollack, then how are we supposed to use them? If you are lucky enough to actually have a local fishmonger, then build up a relationship with him – all fishmongers buy either from markets or direct, so for them it's merely a matter of a phone call to get in a new type of fish for you.

Buying farmed fish may seem like an easy solution to the problem, but as with meat, you need to know the source of the product. Fish farming has had a lot of bad press over the years and it doesn't necessarily solve the problem of the continuing depletion of wild fish. We need to vary our species and make sure we utilise every bit of the fish. Don't leave the bones at the fishmonger – take them home and make a fish soup or a curry with the collar and cheeks.

Hugh's book has proved a real inspiration. I've lifted a couple of recipes from it here, and added a few of my own.

Spaghetti with cockles and three-cornered garlic

Serves 4

British cockles can be as rewarding as clams, and they cost a fraction of the price. I'm talking fresh cockles in the shell here – not the gritty ones you buy at seafood stands alongside the crab sticks. Most good fishmongers will stock live cockles or be able to get hold of them for you. The cockles need to be well rinsed under running cold water for a while and agitated using your hands every so often to remove any grit from their grooved shells.

Three-cornered garlic, or hedgerow garlic, has just started appearing and if you're a forager you will probably have harvested some already. It resembles garlic chives and you will probably have had a whiff of it if you've been on a country walk recently. If you haven't got access to any, then crush about 4 cloves of garlic and cook them with the shallots and toss about 2 tablespoons of chopped parsley in with the spaghetti at the end.

500g spaghetti
100ml white wine
1kg cockles, washed as above
4tbsp olive oil
2 large shallots, peeled, halved and finely chopped
A good pinch of dried chilli flakes
150g butter
A handful of three-cornered garlic
Salt and freshly ground black pepper

Cook the spaghetti in boiling salted water according to the instructions on the packet then drain in a colander, saving a little of the cooking liquid. Heat the white wine in a large saucepan, add the cockles and cook over a medium heat with the lid on, shaking the pan every so often, for 3-5 minutes until the cockles have all opened. Drain in a colander over a bowl to catch the juices and leave to cool a little. Remove half of the cockles from the shell and put to one side.

Meanwhile, gently cook the shallots in the olive oil for a couple of minutes with the chilli flakes, add the butter and the cockle cooking liquor, then toss with the spaghetti on a very low heat, add the cockles and three-cornered garlic and season. The sauce should be just coating the spaghetti – if it doesn't, add a little of the cooking liquor and more oil and butter. Serve immediately.

Mussel, spinach and bacon gratin

Serves 4 as a main course or 6 as a starter

This is a recipe from Hugh's book in which the shells don't feature in the end product. It's a very comforting dish and great for sharing. Mussels are at their best in the colder months and I would strongly recommend using sea spinach if you can can get your hands on it. Sorry Hugh, I've bastardised your recipe a bit here, but I know you like seaside foraging!

2tbsp white wine
1 shallot, diced
1kg mussels, scrubbed and de-bearded
1tbsp olive oil, plus a little more to finish
150g smoked bacon or pancetta, diced fairly small
1 fat garlic clove, finely chopped
About 400ml whole milk
50g unsalted butter
50g plain flour
500g spinach, thoroughly washed, tougher stalks removed
A squeeze of lemon juice
75g fresh white breadcrumbs
50g cheddar or Parmesan cheese, grated (optional)
Freshly ground black pepper

Place a large pan over a high heat and add the wine, 2 tablespoons of water and the diced shallots. Bring to a simmer, then throw in the mussels and cover with the lid. Let them steam open in the pan for 3-4 minutes, shaking the pan once or twice. Remove the mussels from the pan with a slotted spoon (discarding any that have remained fully shut) and set aside until they are cool enough to handle. Pick the mussels from their shells and set aside. Strain all of the cooking liquor through a fine sieve, or a coarse sieve lined with a cloth.

Heat the olive oil in a frying pan, add the bacon and sauté gently until it starts to crisp up. Add the garlic and cook for a further minute or so, being careful not to let it burn. Remove from the heat and transfer to a bowl.

Now you need to make a béchamel sauce. First combine the reserved mussel cooking liquor with enough milk to make 500ml and heat gently in a pan. Melt the butter in a separate pan. When it is foaming, add the flour and stir well to make a smooth roux. Gradually add the warmed milk, stirring well after each addition to prevent lumps. Bring to a simmer and cook gently for 4-5 minutes to give a smooth, creamy sauce.

Drop the spinach into a large pan of boiling water and cook for a minute, until wilted. Drain, leave to cool, then squeeze out excess water with your hands. Chop the spinach roughly.

Fold the bacon, mussels and spinach into the béchamel sauce. Season with freshly ground black pepper and a squeeze of lemon juice. Divide the mixture between 4 buttered shallow ovenproof dishes (or 6 ramekins if you're serving it as a starter) or spread it evenly into a large buttered gratin dish.

Sprinkle over the breadcrumbs, plus the cheese if using, and trickle over a little olive oil. Bake in an oven pre-heated to 200C/gas mark 6 for 10-12 minutes, until golden and bubbling. Serve piping hot, with crusty bread.

Red mullet woodcock style

Serves 2

Red mullet is sometimes called Bécasse de mer (woodcock of the sea) as, like a woodcock, the livers are highly prized. Hugh has mixed the livers here with various, almost Mediterranean, seasonings to emulate the traditional preparation of the woodcock.

2 very fresh red mullet (350-500g), descaled and gutted, livers reserved
1tbsp olive oil
25g unsalted butter
1 small clove of garlic, unpeeled
1 bay leaf
2 green olives, stoned and finely chopped
1 anchovy fillet, finely chopped
1tbsp white wine
Salt and freshly ground black pepper

Remove the livers from the fish and set aside. Season the fish. Place a large non-stick frying pan over a medium-low heat. Add the oil and butter, the garlic clove and then add the whole fish. Sizzle gently for about 8-10 minutes, then turn them over and continue cooking for 6-7 minutes or so, until cooked right through. Remove from the pan and keep warm.

Keeping the pan on the heat, remove the cooked garlic clove, then peel and chop it – it shouldn't be too burnt if you have cooked the fish gently. Combine it with the chopped olives and anchovy. Add this mixture to the hot pan, along with the livers and wine. Sauté for just half a minute to reduce the wine a little, then remove the pan from the heat and mash everything together with a fork.

Smear this paste over the skin of the mullet, and serve, accompanied by plain mash or sautéed potatoes and seasonal vegetables.

Blue swimmer crab soup

Serves 4-6

I spent a few days over the New Year down at Mitch Tonk's house in Brixham, Devon. We cooked up a storm on New Year's Eve with lightly salted pollack cooked in olive oil with the most buttery mash ever (pommes mousseline actually) and delicious Dexter beef chops cooked on the Okabashi grill – the rest of my stay turned into a bit of a blur.

During the day, the younger kids went crabbing off the marina pontoon with Robin Hancock of Wright Bros, the oyster bar in Borough Market. They proudly brought back a few blue swimmer crabs in their bucket and that gave me the idea of making a sauce to go with a whole baked turbot that we were planning to eat that night. The kids perched themselves on stools near the cooker armed with a wooden spoon and I took them through the process of making crab sauce. It was delicious; so much so that most of it was consumed before dinner, and we had to settle for Hollandaise instead. I'm sure the kids didn't expect their crabbing expedition to turn into a cook-up with such delicious results. So why don't we use blue swimmer crabs more? Even the poor old spider crab doesn't get much of a look-in. In Spain and France they are on display in most fishmongers for soups and stews, but here they are just regarded as a pest to fishermen because they eat all the bait before the brown crabs can get to it.

500-600g blue swimmer crabs
1tbsp vegetable oil
1 small onion, peeled and roughly chopped
1 small leek, trimmed and roughly chopped
3 garlic cloves, peeled and roughly chopped
1/2 tsp fennel seeds
10-15 strands of saffron
A few sprigs of thyme
1 bay leaf
40g butter
2tbsp tomato purée
3tbsp flour
1 glass of white wine
1.5litres fish stock, or a couple of good fish stock cubes in 1.5litres of hot water
100ml double cream
Salt and freshly ground white pepper

Put the crabs in the freezer for about 30-40 minutes then remove them and chop them into pieces. Heat the vegetable oil in a large heavy-based saucepan and fry the crabs over a high heat for about 5 minutes, stirring every so often until they begin to colour. Add the onion, leek, garlic, fennel seeds, saffron, thyme and bay leaf, and continue cooking for another 5 minutes or so, until the vegetables begin to colour. Add the butter and stir well, then add the tomato purée and flour, stir again and cook for a minute or so over a low heat. Add the white wine, then slowly add the fish stock, stirring to get rid of any lumps. Bring to the boil, season with salt and pepper, and simmer gently for 1 hour.

Blend the soup in a liquidiser or a strong food processor then strain through a fine-meshed sieve.

Return to a clean pan, season with a little salt and pepper, if necessary, and bring to the boil. To serve, add the cream and adjust the seasoning again, if necessary, and stir well.

Gurnard in beer batter

Serves 4

There are three species of gurnard regularly caught in the British Isles: the red gurnard, which is the most common, the tub gurnard, which is very similar and often larger though not as common as the red, and the grey, which is the biggest of all three. I used to catch them regularly as a kid by accident when fishing for other species on boats in Lyme Bay and never really appreciated them as a good fish for eating. They would normally be used and sold as bait for lobster and crab pots – but today I have a slightly different attitude towards these great-looking fish.

Gurnard is still underrated, and the larger fish have great eating qualities either simply pan-fried or deep-fried like this – so don't ignore them if you spot them on the fishmonger's slab. You can serve with the obvious accompaniment, chips, or mushy peas – or try making a posh version by blending some frozen, cooked peas coarsely with a little stock and butter and a sprig of mint.

2 large gurnard weighing about 800g-1kg each, filleted and boned
Salt and freshly ground white pepper
Flour for dusting
Vegetable or corn oil for deep frying

For the beer batter

150g self-raising flour
150-200ml light ale or lager

Pre-heat about 8cm of oil to 160-180C in a large thick-bottomed saucepan or electric deep-fat fryer. To make the batter, put the flour into a bowl, then stir in the beer and whisk to form a smooth thick batter, before seasoning.

Season and lightly flour the gurnard fillets then dip into the batter, holding them by the tail and ensuring they are well coated, and drop into the hot fat a couple at a time. Cook for 5-6 minutes, turning them occasionally with a slotted spoon until they are golden and crisp, then remove and drain on some kitchen paper.

Serve with chips and mushy peas.