Anatomy and Function of a Fish

Anatomy and Function of a Fish Reproductive, Nervous, and Endocrine System Part 4

Reproductive System • Reproduction is the process by which organisms produce offspring. • Reproductive organs: • Ovaries • Testes • Genital duct • Fish develop when eggs from the ovaries of a female are fertilized by the sperm from the testes of a male.

Ovaries produce eggs. • Testes produce sperm. • Genital duct: Eggs (in female) and sperm (in male) pass to the outside of the fish. • Fertilized fish eggs develop into embryos, which use the yolk in the egg as food.

Fish have many ways of spawning. • In the ocean, most males and females shed their eggs and sperm into the water in the same place at the same time. • Fertilization takes place externally. • Some females lay eggs in nests, where males fertilize them. • Other fish, including sharks and guppies, fertilized their eggs internally. • They hatch from the eggs inside the female’s body and are born alive.

There are advantages for external spawning. • When sperm and eggs are spawned externally, the parents do not care for the young, so little energy is used in the reproductive process. • When eggs are laid in nests, the parents often care for or guard the developing young. • More of their young survive, but the parents must spend considerable time and energy and may endanger themselves guarding the young.

When young are fertilized internally, only a few eggs are needed, and most of them survive the early stages of development.

Several groups of fish can change their sex. Example: Hawaiian cleaner wrasse • A male cleaner wrasse often has a harem, a group of females that stay with him. • If a male disappears, the dominant female in the harem assumes the male role and within several weeks, her ovaries become functional testes. • Some fish that change sex also change color patterns and behavior.

Nervous System • The nervous system is a complex group of tissues and organs that control most body processes. • Nervous System Organs Include: • Olfactory bulbs • Cerebrum • Optic lobes • Optic nerves • Cerebellum

Medulla • Pituitary gland • Spinal cord • Sensory nerves • Motor nerves

The nervous system uses biochemical signals. • It operates like a telephone system, with a master computer in its central office and a complex of cables and lines linking the parts of the system. • The nervous system has two major divisions: • Central nervous system • Peripheral nervous system

Central Nervous System • The central nervous system consists of the brain and the spinal cord. • The brain receives information from sense organs that monitor conditions both within and around the fish. • The brain interprets this information and sends response commands to the body. • The brain is surrounded and protected by the bones of the skull.

Olfactory Bulbs • The brain of a fish is divided into six major parts, each with a different function. • Olfactory bulbs: (Two) Control the organs of smell. • Sit side by side at the end of long stalks at the very front of the brain. • From the nostrils, they receive information about chemicals in the water. (This is the function. I might ask this on test/worksheet). • Olfactory nerves carry this information to the brain.

Cerebrum • Cerebrum: Consists of two lobes behind the olfactory bulbs. • The cerebrum controls the voluntary muscles and has limited memory. (This is the function.) • Memory is enough to learn simple tasks and adapt to new environments. • In higher animals like humans, this is the thinking part of the brain.

Optic Lobes 3. Optic Lobes: (Two) Located just behind the cerebrum. • Receive information from the eyes. • Responsible for vision. (This is the function).

Optic Nerves 4. Optic nerves: Connect optic lobes to the eyes. • They carry information from the eyes to the optic lobe.

Cerebellum • Cerebellum: Located behind the optic lobes. • Coordinates the movements of skeletal muscles once contraction and relaxation is initiated by the cerebrum. • When the command goes out from the cerebrum to swimming muscles, for example, the cerebellum takes over and ensures that the muscles work in proper rhythm and order.

Medulla • Medulla: Located under the cerebellum. • Connects the brain to the spinal cord. • Has multiple functions. • Controls hormone secretion. • Controls gill muscles for respiration. • Controls heart and muscles for digestion.

Pituitary Gland • The pituitary gland is located beneath the optic lobes. • It is the master gland of the endocrine system of the body. • The function of the pituitary gland is to secrete many hormones.

Spinal Cord • The spinal cord runs through holes in the vertebrae. • It acts like a telephone trunk line. • It is composed of long nerve fibers. • The function of the spinal cord is to carry sensory nerve impulses to the brain and transmit motor nerve impulses from the brain to the muscles, glands, and other tissues.

Peripheral Nervous System • The peripheral nervous system is the network of nerves that connect muscles and sensory organs to the central nervous system. • There are two types of nerves: • Sensory nerves: Carries information from sensory organs to the spinal cord and brain. • Motor nerves: Carry commands from the brain or spinal cord to the muscles and glands of the body.

Sensory Organs • The sensory organs send the information they receive to the central nervous system and the brain. • The general function of the sensory system is to detect changes in the environment and in the body. • The sensory organs include: • Eyes • Semicircular canals • Lateral line • Nostrils • Taste receptors • Ears

Eyes • The eyes of fish resemble human eyes. • The function of the eyes is to detect changes in light to allow the fish to see. • At the front of each eye is a lens held in place by a suspensory ligament. • The lens focuses images of objects on the retina. • To bring near and far objects into focus, the lens retractor muscles moves the lens back and forth.

The retina is a light-sensitive membrane rich in nerves that connect to the optic lobes of the brain by optic nerves. • When lights shine on the nerves of the retina, the optic nerves send impulses to the optic lobes.

Eyelids • The eyelids of humans move up and down (blink) to protect the eye and to coat the surface with fluid (tears). • The fluid keeps the delicate cells at the surface moist so that they do not dry out and die. • Because fish have no eyelids, their eyes are always open. • The eye of fish are in constant contact with the water, which keeps them moist.

Ears • Fish have two inner ears embedded in spaces in their skulls. • The function of the ears is to detect sound vibrations. • The lower chambers, the sacculus and the lagena, detect sound vibrations. • In humans, sound is detected in the cochlea

Otoliths • Small stone-like bones, called otoliths, float in the fluid that fills these chambers. • Like the otoliths in our ears, they help the fish to keep its equilibrium. • Otoliths also enable the fish to detect sound vibrations in the water.

Semicircular Canals • The semicircular canals of the ears detect changes in position and movement and control balance. • A small bulge at the end of each semicircular canal, called an ampulla, contains hair cells sensitive to movement. • When the fish rolls right or left, tail up or tail down, the liquids and otoliths push against the hair-like nerve endings lining the canal, sending messages to the brain.

Lateral line • Running along each side of their bodies fish have a row of nerves that register changes in pressure and water current. • The nerve endings are in a system of tubes and pressure-sensing nerve endings called the lateral line. • When water pressure changes or the fish enters current or another fish swims by, water moves faster through the tubes, activating their nerve endings. • The lateral line runs the length of the fish ending in pores on the head.

Nostrils • The sense of smell is well developed in some groups of fish. • Water circulates through openings in the head called nostrils. • The function of the nostrils is to detect chemicals dissolved in the water. Also used to smell.

In both humans and fish, the molecules from distant objects come in contact with sensitive cells in the nostrils. • Both humans and fish detect these odors. • Fish smell chemicals dissolved in water. • Humans smell chemicals in the air.

Olfactory Bulb • Sensory cells are clustered in the olfactory bulbs located in the forebrain. • When the cells are stimulated by these molecules, a nerve impulse travels to the brain, where the fish smells the substance in the water.

Taste Receptors • In most fish, taste receptors are in the mouth, but some fish have touch-and-taste receptors on their fins or other structures, such as the barbels of a goatfish. • The function of taste receptors is to detect chemicals of objects that touch the mouth or other special structure.

Endocrine System • The endocrine system uses chemicals called hormones to control important body processes. • Hormones can slow body processes, speed them up, or start new ones. • They can control processes such as: 1. Rate of growth 2. Development of sex characteristics 3. Capacity to respond to light and stress

The nervous system sends electrochemical signals to and from the brain at a speed of several hundred miles per hour. • By contrast, hormones act much more slowly than nerve impulses, but they can operate for long periods.

Endocrine Glands • The endocrine glands feed their chemicals into the bloodstream through capillary walls instead of through tubes. • A major endocrine gland is the pituitary, lying under the brain. Ending it Here!! Bring Gloves Tomorrow for Dissection!

Anatomy and Function of a Fish