I find this pretty interesting and it goes to show that the ELF/ULF studies may have some merit:
Electrosensory Organs of Catfish

Asano(1998) studied in detail the electrosensory organs of catfish, and argued that its specific ability should be considered in this connection. Catfish have extraordinary sensitive electrosensory organs all over their skin. The organs are the most sensitive to oscillating electric fields at frequencies from a few Hz to about 100Hz and can detect even 5 microvolts per meter in water in this frequency range. These organs are used as a tool for catching prey by catfish living in a murky habitat where optical senses are of little use.

That was from the page referenced by EQF on catfish.