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Nervous Anatomy
Pineal Organ
Corpus pineale
A light-sensitive organ on top of the fish brain - sometimes called the "third eye," it regulates circadian and seasonal rhythms.
Region: Head Universal in fish Unique to: all
📖 Overview
The fish pineal is a functional photoreceptor, sensing light through the skull and secreting melatonin in darkness. This controls circadian activity, spawning timing, and seasonal migration. Some primitive fish (lampreys, lungfish) even have a visible pineal spot on the skull.
✨ Fun Fact
The lamprey pineal has photoreceptors indistinguishable from those in the retina - a living reminder that the vertebrate brain still contains light-sensitive tissue.
🔗 Related Nervous Structures