Monterey Bay Salmon & Trout Project

Fish have highly developed nervous systems organized around a brain. Fish brains have several clearly visible parts.

The most anterior parts of a fish's brain are the olfactory bulbs. These are connected to the two lobes of the cerebrum by stalks. In fish the cerebrum is primarily involved with the sense of smell. It also seems to control behaviors such as taking care of the young and exploring the environment. The optic lobes process information from the eyes. The cerebellum coordinates body movements and the medulla controls internal organ functions and maintains balance.

Posterior to the brain is the spinal cord, which is the hollow dorsal nerve cord that characterizes chordates. The spinal cord is enclosed and protected by the vertebral column. Between each set of vertebrae, a pair of spinal nerves exits the cord and connects to the internal organs and muscles.

Most fish have superbly designed sense organs. Fish like trout and salmon, which are active in the daylight, have well-developed eyes and color vision nearly equal to the average human. They also have extraordinary senses of taste and smell. Chemo receptors (chemo-means chemical) are located all over the head and much of the body surface. Salmon can distinguish between the odor of their own home stream and that of another stream while they are still far out at sea. Most fish have ears inside their heads, but they do not hear well. However, a series of pores connected to canals beneath the skin cover the head and the sides of their body. This system, called the lateral line system, detects the motion. Some fish-electric eels, catfish, and sharks-can detect electricity.

Reproduction