From Halopedia, the Halo wiki
Electric kesh are marine animals native to the warm equatorial oceans of Sanghelios. They, along with Snap-tails, are known to thrive in underwater limestone ridges and valleys roughly a kilometer away from shorelines. These scaly sea creatures are considered magnificent specimens among Sangheili fishers.  Their name would indicate that they are electrogenic and thus capable of generating electric fields around themselves.
List of appearances
- Halo: Shadow of Intent (First mentioned)
- ^ Halo: Shadow of Intent, page 68 (Google Play edition)