TOKYO (Reuters) - Big Japanese manufacturers grew less optimistic in January-March and they expect business conditions to worsen in the following quarter, a government survey showed on Thursday, underscoring the economy's fragile recovery from recession.

The business survey index (BSI) of sentiment at large manufacturers stood at plus 2.4 in January-March, compared with plus 8.1 in the prior three months, according to the joint survey by the Ministry of Finance and the Cabinet Office.

The BSI measures the percentage of firms that expect the business environment to improve from the previous quarter minus the percentage that expect it to worsen. Positive figures mean optimists outnumber pessimists.

Japanese firms plan to raise capital spending by 5.1 percent in the current business year to March 2015, the survey also showed, more than the 4.9 percent seen in the previous poll. Capital spending is expected to fall 3.9 percent in the next fiscal year.