“A Brain Heater in the Swordfish”, Francis G. Carey1982-06-18 (, ; backlinks)⁠:

The brain and eye of a swordfish are warmer than the water. Associated with one of the eye muscles is a tissue that heats the brain.

This brain heater is rich inmitochondria and cytochrome c and is supplied with blood through a vascular heat exchanger.

It protects the central nervous system from rapid cooling during daily vertical excursions which may take the swordfish through a wide temperature range.