Based on LXX’s και ξηρανθησονται, several pre-Qumran scholars have emended MT to read תיבש (=1QIsaa), which may be derived from √יבשׁ (“be dry,” HALOT, 384). This would explain the absence of the ‘ālep in תיבש as well as the presence of the yôd. Both MT (“their fish stink”) and 1QIsaa (“their fish dry up”) are possible in the context.
But following Kutscher, it is my view that the scroll’s scribe was impacted by the somewhat synonymous √חרב (hip’il, “to cause to dry up, run dry,” HALOT, 349), which appears five words earlier (although this theory does not explain LXX’s reading). Moreover, MT’s תִּבְאַ֤שׁ works well in the parallelism and should therefore be followed.
Donald W. Parry, Exploring the Isaiah Scrolls and Their Textual Variants (Supplements to the Textual History of the Bible 3; Leiden: Brill, 2020), 354