如何理解VOA中的这一句话
前文大意,渔业学生在海上围起来的渔场练习撒饲料喂鱼.
The surface of the water literally bubbles as thousands of cod come up to feed.They're monitored from the boat by an underwater camera.
无法明白之处是"literaly bubbles as thousands of cod come up to feed",整句话意思不明,另外literaly在这里表达什么意思?简要解释即可,