se winstre hranfisc: #leftshark.
(More accurately ‘left whale’ but the best I can do.)
Image: From one of my favourite Tumblr blogs, Erik Kwakkel. Paris, Bibliothèque Sainte-Geneviève, MS 98.
Update 9 Feb 2015–
Since first publishing this post, another word for ‘shark’ has been suggested by @mwnciod on Twitter: sǣ-hund, m.n. It literally means ‘sea-hound’, which could very well be a shark, so says the Old English Wikipedia entry.
So we have se winstre sǣ-hund for #leftshark.