Osteichthyes Lab

NAME _____________________________

OSTEICHTHYES LAB

PHYLUM: Chordates

SUBPHYLUM: VERTEBRATA "bone covering nerve cord"

CLASS: OSTEICHTHYES 'bony fish"

Fishes are the oldest vertebrate group and the most numerous and widespread of all living vertebrates today. 95% of all fish are in the class OSTEICHTHYES meaning "bony fish". All BONY FISH have three characteristics:

1). an endoskeleton made of BONE

2.) lungs or a SWIM BLADDER, and

3.) a body surface covered with SCALES

INTEGUMENTARY:

The skin of the perch is covered with SCALES (thin round discs of bonelike material that grow from pockets in the skin). The scales overlap like roof shingles and point toward the tail to REDUCE FRICTION AS THE FISH SWIMS. Scales grow throughout the fish's life and the resulting growth rings give a good approximation of the fish's age. Scales also PROVIDE PROTECTION.

The fins on a fish are adaptations for swimming and navigation and are supported by RAYS or SPINES which also PROVIDE PROTECTION FROM PREDATORS.

The two DORSAL FINS (one anterior and one posterior) and a ventral ANAL FIN help keep the fish upright and moving in a straight line. The paired PELVIC FINS and PECTORAL FINS are used to stop, move up and down, and even back up. The CAUDAL FIN extends from the tail for propulsion. The ANUS and UROGENITAL OPENING are located near the anal fin.

NERVOUS (Sense organs)

The LATERAL LINE system, which runs along each side of the fish, is a sensory structure which detects water pressure and vibrations in the water. Find the NOSTRILS (dead end pockets) and EYES (with NO EYELIDS).

Fish have a highly developed sense of smell and sight and the parts of the fish's brain that process info from these two areas (OPTIC TECTUM and OLFACTORY LOBES) are the largest parts of a fish's brain.

COLORATION:

Pigment cells (CHROMATOPHORES) in the skin give the fish its color and allow it to blend in with its surroundings. Notice the fish has lighter coloration on its ventral surface and is darker on the top so it is less easily seen from above or below.

RESPIRATORY/EXCRETORY:

On each side of the head is the OPERCULUM, a hard plate that covers and protects the GILLS. Water enters through the fish's mouth, passes over the gills, and out through the slits behind the OPERCULUM.

Water moving over the gills flows away from the head, while the blood inside the gills flows toward the head. This arrangement, known as COUNTERCURRENT FLOW, allows more oxygen to diffuse into the gills than would be possible if blood and water both flowed in the same direction.

The GILLS in a fish serve THREE FUNCTIONS:

1. EXCHANGE OF GASES

(oxygen is taken in and carbon dioxide is released),

2. REMOVAL OF NITROGEN WASTE

(AMMONIA is removed from blood and released)

3. OSMOREGULATION OF WATER/ION CONCENTRATIONS IN BLOOD.

(IONS are actively transported IN or OUT depending on environment

In order to stay alive an organism must keep the balance of ions and water in a constant range. This is done through a process called OSMOREGULATION, which means maintaining the proper balance of water and ions in the blood and body tissues.

FRESHWATER FISH:

Freshwater fish tend to GAIN WATER and LOSE IONS in their HYPOTONIC environment.

The GILLS in a perch (freshwater dweller) have special cells that ACTIVELY TRANSPORT sodium and chloride ions in through the gills to maintain the correct ion balance. The KIDNEYS also remove excess water by making urine. Freshwater fish urinate constantly to remove the excess water that is always entering their bodies from their hypotonic environment.

SALTWATER (MARINE) FISH:

The reverse happens in SALT-WATER fish. Since sea water is HYPERTONIC, water is constantly leaving the fish's body via osmosis and ions are entering through diffusion.

To maintain the water/ion balance, salt water fish urinate less and drink sea water to replace lost water. They excrete the extra ions taken in through special cells in their gills that maintain the proper osmotic concentration in their blood and tissues. Extra ions are also excreted in urine.

INTERNAL ORGANS: Use your scissors to slice along the ventral surface and peek inside to see the SWIM BLADDER (also called AIR/GAS BLADDER). This organ is thought to have evolved from the lungs of early bony fish. Gases (oxygen, carbon dioxide, and nitrogen) from the blood can be added to or removed from the SWIM BLADDER to control the fish's buoyancy. By adjusting the volume of gas in the swim bladder, a fish can remain suspended at any depth with no muscular effort.

MUSCULAR/SKELETAL

Fish are "top heavy" with muscle because the body muscles are concentrated along the dorsal surface and in the tail of your fish. (One of the reasons fish float "belly up" when they are dead). An ENDOSKELETON of bone provides support and helps in movement. Having an ENDOSKELETON allows a vertebrate to grow without molting.

Bones (called vertebrae) surround their SPINAL CORD, as well.

Now remove the skin and muscle on one side of your fish so you can see the internal organs. Fish, like all vertebrates, are EUCOELOMATES. The space you see surrounding the organs is true COELOM. Notice the location of the liver, gills, and heart. It is no accident these vital organs are so close together.

REPRODUCTIVE

Fish have SEPARATE SEXES. The male reproductive system consists