Eating fish on Fridays is a longstanding tradition in Catholic households worldwide dating back to the first century of the modern era.

Why abstain from meat? Why on Friday? Why during Lent?

Meat once was for celebrations and feasting. Early Christians abstained from eating meat on Friday as a kind of sacrifice and reminder that acknowledged the death of Jesus on the cross on Good Friday.

This still holds true today in the Catholic Church, but only on Ash Wednesday, and Fridays during Lent.

It is the shared teaching of various religious traditions that fish belongs on a sanctified table because the eyes of the fish, which in life never close, are a reminder of God's eternal omniscience. (That may explain why so many people prefer filets to whole fish.)

Another reason for fish on Fridays, and on many other days, is that, when cooked well, fish offers is a delicious lean protein alternative to meat.

However, as overfishing has become a serious problem, contributing to the decline of many once common and plentiful species, it is incumbent on shoppers to learn which fish are good choices for sustainable harvesting and eating, and which are better avoided until populations rebound.

Choosing foods with respect for the ecosystems that sustain all life could be viewed as a secular way to sanctify mealtime.

The Environmental Defense Fund works with scientists and environmental groups to offer a unified voice from within the conservation community and to provide consumers with information to make sustainable seafood choices. They have a simple-to-follow rating system that can be found at seafood.edf.org/guide/best.

The best choices include fish from healthy, well-managed populations, and the fishing or farming methods used to catch or raise the fish cause little harm to the environment. Once you've chosen the eco-best fish of your fancy, there are many options for turning this fish into an easy but sophisticated and delicious repast. Broiling, pan-searing, roasting, poaching and grilling are all great options depending on the type of fish and the time of year.

Regardless of the cooking technique, a reliable rule of thumb when cooking fish is that it will take 8 to 10 minutes per inch of thickness to cook fish through. Of course there are exceptions. Some fish and shellfish, such as scallops, are better served à point - barely cooked through - to remain moist and tender. Meatier and fattier fish, such as mackerel, salmon, or bluefish, with an inherent oiliness, tend to stay moist unless significantly overcooked and are best cooked completely.

Fish is done when the fish firms up, is opaque throughout and has a flaky texture. Don't be afraid to take a fork or thin-bladed knife to check your fish for doneness. A temperature of 135 degrees generally means "done." For rare - such as you'd want when cooking expensive, high-quality tuna - a temperature of 120 degrees will suffice. Don't forget to check whether tuna is on the Eco-OK list this month before you buy.

Fish, like all food, will keep cooking when removed from the heat, so err on the side of just under-done. You can always cook something a bit more, but it is impossible to rescue a dry, overcooked fish dish.

With any techniques, you have many seasoning options. Very mild fish, such as flounder, need little more than salt, pepper and a squeeze of lemon. Stronger fish, such as blue, can take onions, garlic, capers, tomatoes, anchovies - as you like. Coconut milk and curry can enliven halibut or cod, and sea bass is always delicious steamed with ginger and soy.

When purchasing whole fish, consider asking the fishmonger to bone the fish, but leave it whole. This "butterflying" technique is common for small trout, but equally appealing for larger fish. Boned, with a head and tail, this fish can be prepared whole - roasted or poached, grilled or stuffed - and served with flair (and no bones to remove at the table).

A popular use for leftover fish, fish cakes, when made from scratch, can be tailored to your taste and to your budget. Whether prepared with leftover baked cod, or canned wild salmon, flaked fish held together with mashed potatoes or bread crumbs, seasoned with sautéed veggies, herbs or spices, these patties can be sophisticated or old fashioned in their simplicity and ease.

With a repertoire of good fish dishes, meatless Friday night can come around every week.

Oven-Poached Trout With Oyster Cracker Herb Stuffing

Makes 4 servings

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8 tablespoons (1 stick) butter

2 butterflied trout, about 3/4 pound each, head on or off

3/4 cup oyster crackers

Grated rind of one lemon

1/4 cup minced scallions or chives (or a combination), additional sprigs to garnish

3 tablespoons dill, minced fine

Salt and freshly ground pepper

1/4 cup fish, clam broth, or water

Juice of the lemon you grated above

Dill sprigs and sliced lemons for garnish

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1. Preheat oven to 425 degrees. Use about one tablespoon of the butter to grease a baking dish large enough to hold two trout. Place the trout on a counter, skin side down, open.

2. In a food processor, or with your hands, crush the oyster crackers, and mix them with 4 tablespoons of the butter, the lemon rind, and the minced herbs, until butter is blended into the mixture and the crackers are reduced to large crumbs. Add salt and fresh ground pepper to taste.

3. Place half of this mixture into the center of each fileted trout, and close the fish over the filling. Repeat with second fish and remaining stuffing.

4. Place both fish carefully in the greased pan, and pour broth or water. Cover with foil, and bake for 10-13 minutes.

5. While the fish is cooking, heat the remaining butter in a small pan over medium heat until it lightly browns and smells nutty. Remove from heat, and add the lemon juice, both to flavor the butter and to keep it from browning further.

6. To serve, drizzle the butter lightly over the fish, and arrange lemon slices, or wedges, and herb sprigs. Cut each trout in half lengthwise to serve.

Per Serving: 574 calories; 47 grams protein; 8 grams carbohydrates; no sugar; 39 grams fat; 187 milligrams cholesterol; 328 milligrams sodium; trace dietary fiber.

Fish Cakes

Makes 4 servings

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2 tablespoons unsalted butter

1/2 cup olive oil

1 small red onion, peeled and diced fine, about 3/4 cup

2 stalks celery, minced fine

1 red or yellow pepper, seeded, and minced fine

1 tablespoon capers (optional), drained if in brine, rinsed if in salt

2 teaspoons hot sauce (Cholula or Tabasco)

1 teaspoon Worcestershire sauce

11/2 teaspoons crab-boil seasoning (Old Bay recommended)

11/2 cup soft bread crumbs

1/2 cup mayonnaise

2 teaspoons Dijon mustard

2 extra-large eggs, lightly beaten

1/2 pound cooked salmon or cod, cooled and flaked with a fork into small pieces

Salt and pepper

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1. Heat butter and 1 tablespoon of olive oil in a large saucepan until shimmering. Add onion, celery, peppers, and capers, and cook for 5-7 minutes until vegetables are becoming softened. Add hot sauce, Worcestershire sauce, crab seasoning, 1/2 teaspoon salt, and 1/2 teaspoon pepper into the saute pan over medium-low heat, and cook until vegetables are quite soft. Cool to room temperature.

2. Heat oven to 350 degrees. Place the bread crumbs on a sheet pan, and toast in hot oven for 5 minutes until lightly browned, tossing occasionally. Cool.

3. In a large bowl, add 1 cup of the breadcrumbs, mayonnaise, mustard, and eggs. Mix well. Add the flaked fish and the cooled vegetable mixture and combine. Season well with salt and pepper to taste. Cover and refrigerate for 30 minutes. Mold into 8 pattie-shaped cakes. Sprinkle the remaining bread crumbs on the top and bottom of each cake, pressing gently to form a thin coating of crumbs on each side.

4. Heat the remaining olive oil in a large saute pan over medium heat. In batches, add the salmon cakes, and pan fry for 3 to 5 minutes on each side, until well browned. Keep warm in a preheated 250-degree oven, and serve hot.

Per Serving: 537 calories; 18 grams protein; 19 grams carbohydrates; 5 grams sugar; 45 grams fat; 147 milligrams cholesterol; 785 milligrams sodium; 2 grams dietary fiber.EndText

Seared Scallop Corn Chowder with Leeks

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5 tablespoons olive oil

1 leek, trimmed and well-washed, sliced into ¼-inch rounds

1 small carrot, sliced

1 tablespoon minced red pepper (optional)

4 cups flavorful fish stock

1 large russet potato, peeled and cut into 1/4-inch chunks

1/2 cup frozen corn

1 cup heavy cream

Salt, pepper

8-12 sea scallops

3 tablespoons fresh chopped herbs such as parsley, chives, or dill EndTextStartText

1. Heat two tablespoons of olive oil in a medium saucepan until shimmering. Add the leeks, carrot, and pepper (if using) and cook for 10-12 minutes until leeks are just lightly browning. Add the stock and potatoes, and cook until the potatoes are soft. Add the corn and cream, taste, and adjust seasoning.

2. Keep soup hot over low heat while the scallops cook.

3. Pat dry the scallops with paper towels, and remove the side muscle. Heat the remaining olive oil in a skillet until quite hot. Sprinkle each scallop with a pinch of salt, and place carefully into the hot pan to sear. Cook one to two minutes on each side. Remove from heat to a warm plate. Scallops will be barely cooked in the center and well browned on the outside.

4. Have four shallow bowls ready. Ideally, these bowls are warm from sitting in a warm spot in your kitchen, or from running under hot water in the sink and drying well. Spoon a serving of hot brothy chowder into each bowl. Top with two or three scallops, and sprinkle with chopped herbs. Serve immediately.

Per Serving: 517 calories; 28 grams protein; 32 grams carbohydrates; 3 grams sugar; 32 grams fat; 81 milligrams cholesterol; 581 milligrams sodium; 4 grams dietary fiber.