Growth in Nigeria, Africa’s biggest economy and oil exporter, slowed in the fourth quarter as crude revenue fell and manufacturers struggled amid a shortage of foreign-exchange for imports. Gross domestic product expanded 2.1 percent from a year earlier, compared with 2.8 percent in the third quarter, the National Bureau of Statistics said in a report on Tuesday. The median of 11 economist estimates compiled by Bloomberg was for growth of 2.85 percent. “These are very poor figures, and worse than expected,” analysts at Lagos-based FBNQuest, including Gregory Kronsten, said in a e-mailed research note on Wednesday. They had predicted fourth-quarter growth of 3.9 percent. “The poor data are the consequence of the exposure of Nigeria’s Achilles heel. The slump in the oil price has eroded government revenues and dramatically reduced the supplies of foreign exchange for an import hungry economy.”