ANY SELF-respecting angler knows the old saying that there are some fish only fishermen will eat. But hardly a fish exists for which there is not an appropriate and delicious recipe.

Conch, carp, ling, sheepshead or mullet -- eating unfamiliar fish is really no stranger than eating innards, like liver or tripe, or the eggs of chicken or fish or the curds of milk. Locally, the selection of fresh and unusual fish is broad. On the waterfront at Maine Avenue and Seventh Street SW, conch go for about $3 per dozen, ling for 60 cents a pound, carp for 50 cents a pound, mullet for about 90 cents and squid for about $1. That's only the beginning of the list.

And if you're talking economy, the men who trade at the wharf are willing to accomodate you. Several said recently they could be bargained down on a purchase, regardless of the poundage involved. Some added, however, that it's up to the customer to start the haggling.

Once you've bridged the gap, with foreign fish names comfortably assimilated into your vocabulary, try to think of why these unfamiliar fish are up for sale. Someone must be buying them. The Maine Avenue crowd says carp goes into East Indian foods; octopus, squid and others into Oriental cuisine and conch into chowders and salads.

There are other ways to cultivate more lasting friendships with these newfound kitchen companions. Learn how to identify a really fresh fish. Maybe the easiest thing to remember is that a fish should smell fresh. To educate yourself as to how "fresh" smells, take a wiff of a rotten one. The eyes should be clear and the fish should be firm to the touch.

The fishmongers at the wharf say they are not allowed to clean the fish they sell. They refer you to the Virgo Fish House ("Fish Cleaned 365 Days a Year"), a tiny shack where two men, armed with a couple of mean knives and two electric instruments reminiscent to barbershop razors, will clean your fish for about 20 to 25 cents a pound. Exercising their craft with silent efficiency, these men are amazing to watch if you're not overpowered by the smell and the flies.

Any creative cook can dress up these new and inexpensive fish friends. Most fish are tasty barbecued on a grill covered with perforated foil and basted lightly with homemade sauce listed below. Bluefish likes a spaghetti-type tomato sauce, as does conch.

A couple of warnings about a couple of fish. When it's not being used in gefilte fish, carp has a reputation for a slightly muddy taste with a lot of small, bothersome bones.

Some fish scholars advocate bringing a carp home alive, holding it in a large tub of clear, running water for a few days and killing it just before cooking.

Others say the fishmonger should be instructed to remove the large "mud vein" from the carp. To eliminate the bone problem, cut the carp every quarter inch or so. This should allow cooking oils to soften the small "y"-shaped bones. Carp likes to be poached "au bleu," in a court bouillion with vinegar or in red wine. It also works on Chinese dishes and curries.

Another warning. Don't be repelled by the ugliness of the poor, homely conch.

Clean the conch meat and cut off its "foot." Then make a scungilli salad (that's Italian for conch), like they do at Umberto's restaurant in Little Italy, in New York. Owner Oscar Ianello was willing to divulge his recipe.

"We steam the conch," he said. "After it's cooled, slice it. Then toss it in a little olive oil, garlic, parsley and lemon. Serve it cold."

Simple enough? Any one of the following recipes rivals that one in ease of preparation and good taste. The first, from Lafayette, La., is especially good for ling. JIMMY OWENS' FRIED FISH Fish, whole or filets Salt Red and black pepper Small jar of mustard Worcestershire sauce Cornmeal Chopped green onions Thinly sliced onion rings

Season fish thoroughly, inside and out, with salt and pepper. Dip in mixture of mustard diluted with enough Worcestershire to make a thin paste. Shake in cornmeal seasoned with salt, red and black pepper. Fry in very hot grease until done but do not overcook. As fish is done, drain and cover with chopped onions and onion rings. Continue making layers of fish and onions.

-- From "The Cotton Country Collection" of the Junior Charity League of Monroe, La. Recipe from Mrs. F.M. McGinn. CONCH CHOWDER (Makes about 8 cups) 5 to 15 conchs 1/4 cup lime juice 1 two-inch cube of salt pork 1 large onion, minced 3 tablespoons of flour 3 cups water 2 cups pared raw potatoes, diced 3 cups cooked or canned peeled tomatoes 1/2 diced green pepper 1/2 bay leaf 1/2 cup catsup 3 tablespoons butter

Beat the conchs in a canvas bag until they begin to disintegrate. Marinate for two hours in lime juice and chop finely. Saute the salt pork very slowly. fRemove and reserve the cracklings. Add the onion and conch to the fat. Stir and cook slowly about five minutes. Sift flour over the mixture and stir until blended. Heat and stir in the water. Add potatoes, tomatoes, green pepper, bay leaf, catsup. Cover and simmer until potatoes are done but still firm. Add the cracklings and butter. Simmer 8 to 10 minutes. Season to taste. -- From "Joy of Cooking" BROILED SHEEPSHEAD (4 servings) 4 fillets Salt and pepper 1/4 cup melted butter combined with 2 tablespoons lime juice Paprika Fresh parsley

Salt and pepper fillets to taste. Baste with butter-lime mixture. Broil four inches from coils, 5 to 8 minutes each side. Remove to platter, sprinkle with paprika and garnish with fresh parsley sprigs. FISH BARBECUE SAUCE 1 cup catsup 1 cup water 1/4 cup white vinegar 2 tablespoons Worcestershire sauce 2 tablespoons prepared mustard 1 garlic clove

Heat all ingredients in a saucepan for about 10 minutes. Remove garlic upon removal from stove. -- From "Southern Fish and Seafood Cookbook" by Jan Wongrey.