These are fish brains.
As you can see here, fish brains develop greatly in the optic lobes and cerebellum, which are concerned with vision and balance respectively.
Did you know that fish can't feel pain? Studies have shown that fish brains are not sufficiently developed to allow them to feel a sense of pain or fear. The awareness of pain, as these studies reveal, come from specific regions of the cerebral cortex, an area that fish do not contain.
As you can see from this diagram here, there is no cerebral cortex. I haven't mentioned the pituitary, which is a endocrine gland about the size of a pea, which sits in a bony cavity. It secretes hormones. The olfactory bulb, as we all know, transmits odors, and works the same and maybe even better for fish. The cerebrum is self-explanatory.
Studies have also shown that humans can manipulate the growth of fish brains. Fish bred in captivity have smaller brains then those in the wild. But if one were to put more variety in a fish tank, something as simple as stones, the fish will develop a significantly larger cerebellum. They nest around these stones and move around less, and become more like their free cousins.
Though eating fish itself has been proven to be healthy for the human brain, eating an actual fish brain is not recommended because of the fucking horrible taste.
And now you know about fish brains!