They are plucked off pizzas and discarded from caesar salads across the country, but somebody, somewhere has been eating too many anchovies. The fish that has divided food fans for years is today named on a list of unsustainable fish and shellfish that ethical consumers should not eat.

Anchovy is among dozens of "fish to avoid" highlighted by the Marine Conservation Society (MCS). Anchovy populations in the Bay of Biscay have been struggling since 2002, as overfishing left fewer adult fish to provide eggs. The fishery suffered a complete failure in 2004 and is now officially closed. Stocks in the other big European anchovy fishery - off the Portuguese coast - are also critical. Anchovies are still legally caught there, though quotas have been restricted.

In a report on hundreds of types of fish, the society has awarded each kind a ranking from 1 to 5, after assessing its biology, stock status, management and the impact of the farming or fishing method. Sixty-nine received the worst rating of 5, including monkfish from north and northwest Spain, North Sea cod and dogfish. Others to avoid include the Atlantic salmon, common skate and swordfish.

The society's list does not label entire species unacceptable to eat, but tries to explain that whether a certain type of fish is sustainable or unsustainable depends on where and how it was caught. It gives Dover sole caught by wasteful beam trawling in the North Sea and Irish Sea a 5 rating and says they should be avoided, while those from a sustainable fishery off Hastings are rated 2 and recommended.

Such detail is rarely made available to consumers, with current legislation only requiring the common name and rough geographical location to be included on labels. The society is calling for better labelling in restaurants and shops to help consumers choose more environmentally-friendly options.

Sam Wilding, a fisheries officer with the society, said: "Labelling of seafood sold in the UK is lacking detail, and as such is not fit for purpose. This is leading to confusion. It is vital that consumers are given better information to act upon if we are to reduce the tragedy of overfishing."

He said anchovies in European waters were at an all-time low. "There are not many anchovy left in European waters, and we say people should avoid them, to give populations a chance to recover."

Willie Mackenzie, oceans campaigner at Greenpeace, said: "You pick up some tuna in a supermarket and it might say it comes from the Indian and Pacific oceans. Well, that covers half the world, it could be one of several different species, and it could have been caught in lots of different ways. We really need better labelling with more detailed information to help consumers do the right thing."

Chris Brown, head of ethical and sustainable sourcing at Asda, said more detail risked confusing customers. He said Asda stocked marlin, which features on the MCS's "fish to avoid" list, but claimed it was sustainable because it was not deliberately targeted, but caught as inevitable "by-catch" in a sustainable tuna fishery off Sri Lanka, and would otherwise be disposed of. "I can't write all of that on the label," he said.

Brown said it was down to retailers to take more responsibility, and accused some restaurants and supermarkets of confusing the situation by selling sustainable ray, but labelling it as unsustainable skate, because customers are more likely to buy familiar species.

The society said cod demonstrated why precise labelling was important, with cod from the north-east Arctic a more sustainable choice than those from the North Sea.The MCS has certified some cod fisheries in the Pacific as sustainable, and also said consumers could choose organically-farmed Atlantic cod. Wilding called on shoppers and diners to ask more questions about the source of their fish. "Our advice is to ask the waiter or waitress. They might not know at the moment but part of what we're trying to do is to improve training, and raising awareness is important for that." He said the society had produced a pocket-sized version of the list that could be used as a reference.

Philip MacMullen, head of environmental responsibility at the industry body Seafish, said: "It is genuinely difficult to be sure of all the details of any given fish supply line. To this extent advice given via lists ... must match the reality of the available information. We should not be raising unrealistic expectations. The complexities of fisheries also mean that it is difficult to rely on a simple eat-and-avoid list. Fish stocks are dynamic and can change their status quite quickly."