This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 鯐 is uncertain. It visually combines 魚 (fish) and 走 (run), but the original purpose and formation are unclear.
The kanji combines 魚 (fish) and 走 (run). Picture a fish that runs or darts through the water, but remember its actual meaning is uncertain.
For すばしり, imagine a fish that is so swift it seems to 'sprint' (走り) like a 'submarine' (すばしり): the fish runs underwater, and the reading is すばしり.