Chapter 10 Vertebrate Fishes

Overview “Fish” has many usages extending beyond what are actually considered fish today (e.g. starfish, etc.). A modern fish is an aquatic vertebrate with gills, limbs (if present) in the form of fins, and usually with a skin covered in scales. With over 26,000 living species, fish include more species than all other vertebrates combined.

Overview They are adapted to live in a medium 800 times more dense than air. They can adjust to the salt and water balance of their environment. Their gills are efficient at extracting oxygen from water that has 1/20th the oxygen of air. A lateral line system detects water currents and vibrations, a sense of “distant touch.”

Fig. 24.1

Fig. 24.2 Fig. 24.2

Cartilaginous Fishes Approximately 600 species Skeletons composed of cartilage Teeth-like scales Lack gill covers Lack swim bladder Have spiracles – breathing holes behind the eyes Pores in shark’s snout contain nerve receptors that pick up electrical currents Lateral line organ detects vibrations in water Have internal fertilization

Bony Fishes These are the dominant fishes today More than 25,000 species Skeletons composed of bone Backbone made up of individual bones called vertebrae Has mucus-covered scales, which have growth lines that form bands (circuli), used to determine the age of the fish Have gill coverings called the operculum Have swim bladder

Class Osteichthyes (Bony Fishes)

Jawless Fishes Living jawless fishes are represented by hagfishes and lampreys. About 43 species of hagfishes are known and about 41 species of lamprey are described. Evolved from invertebrates Lack a true backbone Possess a notochord for support Live as parasites by attaching to, and feeding on the blood and tissues of a host fish

Class Agnatha (Jawless Fishes)

External Anatomy of a Bony Fish

How Does a Bony Fish… Sense its environment? Swim? Breathe?

Acoustic Senses The ears of a bony fish function in equilibrium, detecting acceleration, and hearing. The lateral line is a system of sense organs found in aquatic vertebrates, used to detect movement, vibration, and pressure gradients in the surrounding water. ... For example, fish can use their lateral line system to follow the vortices produced by fleeing prey.

Acoustic Senses In bony fishes, frequency range of sound production does not appear to be correlated with hearing sensitivity. Most species of bony fishes probably detect prey by sound. In water, sound travels more than four times the speed of sound through air.

Eyesight Bony fishes have a basic vertebrate eye, with various structural adaptations. A bony fish's eye includes rods and cones. Bony fishes, especially those that live in shallow-water habitats, probably have color vision. Certain visual cells are specialized to particular wavelengths and intensities. The eyesight in some species of bony fishes may be well developed. Goldfish have excellent visual acuity up to 4.8 m (16 ft.) away. Some species of bony fishes have no eyes. The blind cavefishes have no vision perception. Other senses help them find prey. The blind goby is born with eyes that degenerate as the goby matures.

Taste Bony fishes have taste buds in their mouths. Some species have taste buds along the head and ventral side of the body. Taste perception hasn't been extensively studied in bony fishes. Some species can detect some sensations, such as salty, sweet, bitter, and acid stimuli. Taste may be responsible for the final acceptance or rejection of prey items.

Smell Olfactory cells in the nasal sac detect tiny amounts of chemicals in solution. In general, the sense of smell is well developed in fishes. The nasal areas and extent of the sense of smell vary among species.

Electroreception Some bony fishes produce a low-voltage electric current that sets up a field around the fish. Tiny skin organs on the fish detect disruptions in the electric field that are caused by prey or inanimate objects. Electric organs are made up of cells called electrocytes that have evolved from muscle cells. Electrocytes typically are thin and stacked on top of one another. Electroreception is an adaptation for detecting prey and for navigation in murky water. Some other fishes produce stronger electric currents for stunning prey.

Locomotion in Water Speed Most fishes swim maximally at ten body lengths per second; a larger fish therefore swims faster. Short bursts of speed are possible for a few seconds.

Mechanism The trunk and tail musculature propels a fish. Muscles are arranged in zigzag bands called myomeres; they have the shape of a W on the side of the fish. Internally the bands are folded and nested; each myomere pulls on several vertebrae. Fig. 24.Fig. 24

Mechanism Fish undulations move backward against the water, producing a reactive force with two parts. The thrust pushes the fish forward and overcomes drag. The lateral force makes the fish’s head “yaw”; a large and rigid head minimizes yaw. The swaying body generates too much drag for fast speed. Fast fish are less flexible and generate all thrust with their tails. Fast oceanic fish have swept-back sickle-like tail fins, similar to high-aspect ratio wings of birds. Fig. 24.25

Fig. 24.18 Fig. 24.18

As different as a man may be from a fish, both creatures share some fascinating similarities in basic structure and function. Man and fish share such organs as the brain, stomach, liver, and kidneys. Other organs appear in different forms in different organisms; for example, the lungs in humans and the gills in fish are very different but both provide the same basic function of respiration. Finally, some organs (such as the fish's swim bladder) are simply not present in man.