This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮱 combines 魚 (fish) with 老 (old). It is likely a kokuji created in Japan to represent a specific fish name, but the exact historical development is uncertain.
The left side is a fish 魚 and the right side is old 老. Picture an old, wise fish that has lived a long time, but remember its actual meaning is unclear.
For おおぼら, imagine an old fish named Oobora: the old fish 老 + 魚 is Oobora (おおぼら).