French investigators will begin examining the black box data recorders from the Air France Rio to Paris flight that mysteriously crashed over the Atlantic in June 2009, killing all 228 people on board.

The two flight recorders were shown to journalists for the first time as they arrived in Paris after being fished from the ocean bed off Brazil, where they had lain two and a half miles down for almost two years.

The boxes – which are fluorescent orange rather than black, so they can be seen in wreckage – have been preserved in mini aquariums that imitate the conditions of the water they were found in.

They were transported, under French armed guard, via French Guyana after being recovered at the beginning of May following a record-breaking 23-month search that many had feared would be fruitless.

Scientists from France's BEA air accident inquiry agency at Le Bourget airport, north of Paris, will immediately begin the painstaking task of checking whether the information held by the boxes is still intact and possible to read.

The flight data recorder should hold the technical co-ordinates of the flight of the Airbus A330 jet, and the cockpit voice recorder should contain the pilots' final conversations.

If this information is readable, the boxes will yield the secrets of the crash of Flight AF447, which dropped into the ocean in unexplained circumstances.

The boxes will be examined under microscope and then tested electronically before technicians attempt to extract the data from memory cards.

Jean-Paul Troadec, of BEA, said that, if the cards were relatively intact, it would take a few hours to obtain the data. Months of analysis would follow in order to establish what happened.

But if the cards had degraded at the bottom of the ocean it was impossible to say how long it would take to extract information. He said it would be clear by Monday whether the cards were readable.

The report into the crash will not be ready until the end of this year at the earliest, but it is more likely to be ready at the start of 2012.

French authorities also announced that they would not recover all human remains from the ocean bed wreckage if it became clear that their decomposition made identification impossible.

Last week, the first body was retrieved, still strapped to its seat. The remains appeared partially decomposed. A second body was later recovered.

Investigators said it would take until next Wednesday to establish whether DNA identification was possible.

Experts had warned that the cold temperatures and lack of oxygen on the deep ocean bed could mean bodies were comparatively well preserved. But they could rapidly decompose as they are abruptly moved to warmer surface waters and into the air.

Families have been divided over whether to recover the victims' remains, with some wanting a funeral to be held and others wanting to leave the bodies where they are. About 50 bodies are known to be in the wreckage.

A judicial investigation for manslaughter against Airbus and Air France was opened in France in March.