crib safety

Claire
This may be a silly question. Last night I put Bear, 5.5 months, in his crib for the first time. He's been in a co-sleeper but he's now too big, so I've moved his crib in to our room. This is a photo of the crib. Last night I heard him snuffling and when I checked on him his arm had got through the gaps. Do you think it's dangerous? Is there anything I can do?