Selfish fish sweat blood swiming in the sea!

中文翻译：自私的鱼在海里拼命地游着.
另外帮你在查到了一些sweet blood的用法：
1.The student sweat blood while wait for the examination result.
学生们焦虑不安地等待考试成绩.收藏指正
2.They are all sweat blood to get the work finished before Friday
为了赶在星期五前完成,他们都在拼命做收藏指正
3.In the last century,there were no trade unions,and so workers could be made to sweat blood.
上个世纪没有工会,因此人们可被驱使着累死累活地干活.收藏指正
Selfish fish sweat blood swiming in the sea!
中文翻译：自私的鱼在海里拼命地游着.

的确

1楼说的没错，字面意思就是“自私的鱼在海里拼命地游着”，或者说，自私的鱼即使是在海里也会焦虑不安。
延伸一下，应该有类似“小人常戚戚”的意思在吧。