fresh-water catfish, (kokuji)
鯰 centers on the freshwater catfish, a specific fish species. It is a kokuji, a kanji created in Japan, so its meaning is tightly bound to that one creature.
鯰 is a kokuji formed by combining 魚 (fish) with 念, which likely contributes the sound ネン. It was created in Japan to represent the freshwater catfish.
The left side 魚 means fish, and the right side 念 suggests the idea of something sticky or clinging, like a catfish's smooth, adhesive skin. Picture a fish that seems to cling to the riverbed.
For ネン, imagine a catfish named Nen swimming in a pond: Nen -> ネン, and the fish's whiskers twitch as it glides through the water.
catfish (esp. the Amur catfish, Silurus asotus)
Wels catfish (Silurus glanis)
Lake Biwa catfish (Silurus biwaensis)
(person) slippery as an eel
electric catfish (any species of family Malapteruridae, esp. species Malapterurus electricus)
upside-down catfish (Synodontis nigriventris)
electric catfish (any species of family Malapteruridae, esp. species Malapterurus electricus)
woodblock print depicting a giant catfish (popular in Edo after the 1855 earthquake)