Fish

What are Fish?

• Fish are aquatic vertebrates (animals with backbones) with fins for appendages. They "breathe" by means of gills.

• Fish make up the largest of the vertebrate groups with well over 20,000 species. Most taxonomists recognize 45 orders and 435 families of bony fishes. They can be found in a great variety of habitats in lakes, streams, oceans and estuaries.

Classification• Kingdom- Animalia• Phylum- Chordata• Sub Phylum- Vertebrata• Classes- Agnatha, Chondrichthyes, Osteichthyes

Characteristics of Subphylum Vertebrata

A notochord that has developed into a spinal cord protected byvertebrae and a head with a brain characterize organisms inthis subphylum.Vertebrates consist of the most complex, large, fast, and conspicuous

organisms. They include us, the organism that has had the most effect on the global biosphere.

Significance of Class AgnathaThis is the class of the jawless fish.

Species include lampreys and hagfish.Organisms in this class are significant because they may

represent the ancestor of bony fish/sharks.Scientists theorize that during the Cambrian period the first

of three gill arches on a jawless fish evolved into the first jaws. Having jaws allowed vertebrates to become very successful predators. Having jaws put organisms in class Chondrichthyes (sharks and rays) and class

Osteichthyes (bony fish) near the top of marine food webs.

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Figure 24.01

16.2

Figure 24.02

Classification of Fish

• Fish are classified according to the material which makes up their skeletons.

• Sharks, skates and rays belong to a group called cartilaginous fish because their skeletons are composed entirely of cartilage.

• Tropical fish are called bony fish (scientific name Osteichthyes) because they have skeletons made of bone.

AgnathaJawless fish: Lampreys, Hagfish

Types of Agnathans• Hagfish- Ocean

scavengers, not much is known about them.

• Lamprey- fresh and salt water, they are parasitic and prey on other fish.

* Both have cartilagenous skeletons and sucker-like mouths.

16.2

Figure 24.02

ChondricthyesCartilagenous Fish: Shark, Ray

Chondrichthyes• Sharks are adapted for a predatory

lifestyle.• Cartilage skeletons, stiff pectoral fins

(speed).• No operculum, must keep moving to

breathe.• Have live births.• Special scales feel like sandpaper.• Manta, and Sting Rays- live in

shallow water, have mouths located on the underside, are fairly docile, wide flat bodies and wing-like fins that are flexible.

Types of Chondrichthyes• Sharks and Rays-

have no operculum and must keep moving to breathe.

• Have different kinds of scales that feel and look more like sandpaper.

• Have skeletons made of cartilage not bones.

Characteristics of Sharks and RaysClass Chondrichthyes includes sharks, rays and their close relatives.

Sharks and rays don’t look similar on the outside, butshare a basic anatomy that classifies them together.

Sharks and rays are jawed fish, that lack a swim bladder, and have cartilaginous skeletons.

Special Attributes of Sharks and RaysSharks and rays are successful predators:

Subclass Elasmobranchii have cartilaginous skeletons. This characteristic saves energy. Saving energy is one of the

things that have made them successful predators.Sharks have a sense of smell that detect incredibly

diluted substances.Sharks have a “conveyor belt” of multiple rows of teeth.

They swing into place as old teeth wear out and fall away.

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Special Attributes of Sharks and Rays (continued)

Sharks and rays have other interesting characteristics:Both have lateral lines – lines of sensory hair along the

length of the body that detect water motion and vibrations.

Unique to elasmobranchs is electroreception – the ability to sense minute electricity created by muscles and nerves.

Sharks and rays have organs called ampullae of Lorenzini which you can see as visible pits near their snouts used to detect the electrical current.

Special Attributes of Sharks and Rays (continued)

Elasmobranchs differ in their reproductive strategy.Sharks and rays produce fewer, but more mature offspring.Most fertilize their eggs internally.

The male deposits sperm in the female via a pair of copulatory organs called claspers found at the base of the pelvic fins.

The female lays an egg case in which the juveniles develop for up to six months at which time one or more sharks or rays emerge.

A few shark species are ovoviviparous – the eggs hatch within the mother’s body.

They give birth to live young rather than egg cases.

The largest fish in the ocean.Shark size ranges from hand-sized to the

whale shark – the largest fish in the ocean. Whale sharks can reach 14 meters (46 feet). Basking sharks can reach 10 meters (33 feet). Megamouth sharks can reach 6 meters (20 feet).

All three are filter feeders that consume plankton.

Special Attributes of RaysSuperorder Batidoidimorpha of subclass Elasmobranchii consists of the

rays, which includes skates and guitarfish.Ray anatomy is well suited to life on sandy

bottoms or midwater.Specially adapted to life in midwater are

the eagle ray and manta ray.Pectoral fins have become “wings” that

stretch forward over the gills and are fused to the sides of the head.

Shoulder girdles are flattened and many bones are fused together for rigidity.

No longer need a tail for swimming, the tail has become a defensive whip in some species.

Rays literally fly through the water.The largest rays are mantas with wingspans

exceeding 8 meters (26 feet).Like the largest shark, the mantas feed on plankton.

Figure 8.14a

Figure 8.12a

Figure 8.04

Figure 8.05b

Figure 8.06b

Figure 8.07

Figure 8.08a

16.2

Figure 24.02

Fish Characteristics• Gills• Backbone (vertebrae)• Paired Fins• Single Loop Circulation• Two chambered heart

Types of Osteichthyes (Bony Fish)

Ray Finned: – Most fish are this type– Fins are supported by bony

structures called Rays.– Teleosts are the most advanced

form of ray finned fish (symmetrical tails and mobile fins).

Lobe Finned:– Fins are long, fleshy, muscular,

supported by central core of bones.

– Thought to be ancestors of amphibians.

– Examples are: Coelacanth, Lungfish

5 - 28

Characteristics of Bony FishClass Osteichthyes are jawed fish with bone skeletons.

Most have a swim bladder and scales.Most control buoyancy by adding or releasing gas to/from their swim

bladder. They control the swim bladders with oxygen gas exchanged to and from blood

circulation. Many have a special organ called the gas gland and the rete mirabile that

take up gases from the bloodstream for the swim bladder. This allows many species to hover nearly motionless in midwater.

Most bony fish reproduce externally.The female lays her eggs, the male

immediately fertilizes them. Their strategy is to produce a vast number

of off-spring with only a few expected to survive to maturity.

5 - 29

Characteristics of Bony Fish (continued)

Bony fish have characteristics for life on the reef and for life in theopen ocean:Bony fish have lateral lines that detect water

motion and vibrations.Most open ocean and schooling fish have a torpedo-like

streamlined shape that minimizes drag and turbulence. This fusiform shape is spindle-like, slightly broader at the

head and a V-shaped tail. This makes them fast swimmers.Most open-ocean and schooling fish have a lighter underside and

dark topside for concealment.Bony fish living in reefs and on the bottom use

survival strategies more diverse and includeconcealment and armor instead of swimming.For this reason, you see far more diversity in color,

shape, and size among reef and bottom fish.

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Figure 8.08b

Fish Anatomy

Fins

Figure 8.12b

Figure 8.14b

Fish Anatomy

Fins

Fish Respiration• Water flows over Gills as fish

opens mouth and swims.• Water flows opposite

direction of blood flow.

• O2 diffuses from the water into the blood.

• Gills are made of thousands of gill filaments.

• Gills are covered by the Operculum.

Figure 8.15

Up Close and Personal

Gills

• Oxygen enters the bloodstream and carbon dioxide diffuses out at the gills, which are feathery structures found along the sides of the head.

• The gills of a healthy fish are bright red due to the high level of oxygen in the blood that is very close to the surface of the gills. (Without oxygen, the gills would be brown.)

• In bony fish, the gills are covered by a bony place called an operculum.

Skin

• The skin of most bony fish is covered with bony scales that look like shingles on a roof.

• Bony fish scales are waterproof and help protect the fish.

• Glands in the skin in which the scales are embedded secrete a layer of mucus that covers the entire body

• Mucus helps protect fish from infection.• Handling fish removes this mucus coating and

can be harmful to the fish.

Shape

• The shape of a fish's body tells a lot about its lifestyle.

• Fish with fusiform, or streamlined, bodies are usually fast swimming predators that may swim at high speeds much of the time or are capable of great bursts of speed.

• Many tropical fish are laterally compressed (flattened from side to side).

• Fish with this shape are not very streamlined but they do not rely on speed for catching food or escaping from predators.

• Their body shape is perfectly adapted for hiding in the cracks and crevices of rocks and reef.

• They can move into these areas to hide, to escape predators or to get at food that cannot be reached by other fish.

• Fish with this body shape, like angelfish, are very maneuverable and capable of short bursts of speed.

• They are often camouflaged with disruptive coloration.

• Other fish are flattened from top to bottom. • Fish with this body shape spend most of their

time at the bottom. • They are usually camouflaged or can change

color to match the bottom.

• Fusiform(Streamlined)

• Laterally Compressed(Flattened from side to side)

• Depressed(Flattened from top to bottom)

• Eel-Like(Body shaped like a snake)

Fins

• Fins are used for swimming and sometimes for protection.

• Some fins are paired and others unpaired. • The paired fins are the pectoral and pelvic

fins. • The unpaired fins are the dorsal, caudal (tail)

and anal fins.

• The way the fins are used varies among different groups of fish.

• Most fish use their tails to move through the water and their other fins to steer with.

• Fins are most bony fish are flexible and supported by visible spines and rays.

• The shape, location and size of a fish's fins are closely linked with its way of life.

Pectoral Fins

• The paired pectoral fins are usually responsible for turning, although they can be used for other functions such as tasting, touching, support and as a source of power for swimming.

Pelvic Fins

• Paired pelvic fins add stability and are used for slowing some bony fishes.

Dorsal Fin

• This may be a single fin or be separated into several fins. In most bony fishes, the dorsal fin is used for sudden direction changes and acts as a "keel" to keep the fish stable in the water.

Caudal (or tail) fin

• This is responsible for propulsion in most bony fishes

Anal Fin

• The anal fin adds stability.

Tails• The shape of the tail can be an indicator of how

fast a fish usually swims.• Crescent-shaped: Fish with crescent-shaped tails

are fast swimmers and constantly on the move.• Forked: Fish with forked tails are also fast

swimmers, though they may not swim fast all of the time. The deeper the fork, the faster the fish can swim.

• Rounded: Fish with a rounded or flattened tail are generally slow moving, but are capable of short, accurate bursts of speed.

• Fish with continuous caudal fins (dorsal, caudal, and anal fins attached) are able to swim in and around cracks and crevices.

• Fish with lunate caudal fins tend to be the fastest fishes and maintain a rapid speed for long durations.

• Many continuously swimming fish have forked caudal fins.

• Fish with truncate caudal fins are usually strong, but slow, swimmers.

• Fish with rounded caudal fins are usually strong, but slow, swimmers.

Eyes

• Fish are visual predators. • Many nocturnal fish have large eyes to help

them feed at night. • Fish such as sharks have pupils that dilate and

constrict, and some sharks also have an eyelid that closes from the bottom upward.

• Bony fish eyes lack both of these characteristics.

Mouths

• The position of a fish's mouth gives a general indication of where it feeds in the water column.

• Fish with up-pointing mouths like hatchetfish primarily feed on the food flakes that float or hang near the water surface.

• Some fish with mouths on the underside of their head, like the catfish, feed on the bottom.

• Large For eating whole fish or chunks of fish

• Small For nibbling on plants and small animals

• Dorsal For eating near the surface

• Anterior For eating in the water column

• Ventral For eating on the bottom

Breathing Underwater

• Fish, like most organisms, need oxygen to survive.

• The oxygen that fish "breathe" is dissolved in the water.

• The oxygen enters the water surface by diffusion or in the water from plants as a byproduct of photosynthesis.

• Water enters the fish's mouth, moves across the gills and passes out the gill slits or operculum.

• The gills are made up of a bony or cartilaginous arch supporting a large number of paired gill filaments.

• Numerous small projections with very thin membranes on each filament are the sites of gas exchange (oxygen to carbon dioxide).

• Beneath the thin membrane is a network of blood vessels.

• Oxygen diffuses from the water through the membrane into the blood and carbon dioxide diffuses outward.

Senses

Sight:

• Most fish have well-developed eyes on the sides of their heads.

• This placement allows them to see in all directions.

• The structure of the eye is very similar to that of other vertebrates.

• In fish, focusing on near and distant objects is achieved by moving the lens backward and forward by muscular action.

• Fish that are colorful can probably see in color.

• Bony fish that are active at night have large eyes that help them see in the dark.

Smell:

• Fish can smell odors in the water with receptors inside blind sacs, called nares, located on the head.

• Nares are similar to our nostrils, but fish do not use them to breathe.

• The sense of smell is well developed and is useful in detecting distant odors.

Taste:

• For fish, taste is more of a close range sense. • Taste buds, which can be found on different parts

of the fish, are used in the identification of food. • Taste buds are located in and around the mouth,

and, on some fish, on the skin and even on the fins.

• Barbels, whisker-like structures near the mouth of fish such as catfish, are covered with taste buds and are used in locating food.

Hearing:

• Fish have ears but they do not open to the outside and cannot be seen.

• Hearing in fish is well developed. • Water carries sound much better than air and

the sound waves are picked up through the fish's body.

Lateral Line:

• A line of holes runs along both sides of a fish from the head to the tail.

• The holes have nerve connections that are sensitive to vibrations.

• The lateral line is used form schooling, avoiding obstacles and detecting prey and predators.

Electroreception:

• Some bony fish can detect weak electrical fields through pit organs on their heads and faces.

• This ability is used for locating prey (all living things give off weak electrical fields), avoiding obstacles in murky water and in migrating.

Buoyancy

• Neutral buoyancy, the ability to remain motionless in the water without rising or sinking, is of great importance to a fish.

• It allows a fish to spend energy feeding, escaping predators or mating that would otherwise be needed to maintain its position in the water.

• Several strategies help achieve neutral buoyancy.

• Most bony fish have a structure called a swim bladder, which is a balloon-like organ in the body cavity.

• Gases from the blood are added or removed to control buoyancy at different depths.

Fish Behavior

• Behavior is the action of a fish in response to its environment including other animals.

• The most interesting and sometimes the most obvious behaviors involve interactions with other individuals.

Migration:

• Many species of fish migrate during their life cycle.

• It is well known that salmon make long migrations to spawn.

• Other fish migrate in response to changing environmental conditions, such as temperature or abundance of food.

Schooling:

• Many fish congregate in groups called schools.

• A school is a group of similarly-sized fish of the same species aligned and swimming in the same direction.

• Sight seems to be the primary means of maintaining the school.

• The lateral line may also be used.

Aggression:

• Aggressive behavior is an interaction between two fish of the same species (intraspecific) or different species (interspecific).

• It is usually associated with reproduction or the defense of feeding territory.

• It includes posturing, direct attacks and displays such as fin flaring and changes of color.

Resting:

• Some fish spend a good portion of their day resting.

• Resting reduces competition, provides protection from predators and may help in energy conservation.

Communication:

• Senses play an important part in fish communication.

• Visual communication is important to most fish.

• Body movements, postures, colors and color patterns are the primary means of visual communication.

• Sound is also used for communication. • Sounds are produced by grinding teeth,

flexing or contracting muscles and vibrating the swim bladder.

• Fish also communicate by releasing chemicals called pheromones.

• These are chemical signals produced by an animal that, when released, influence the behavior of others of the same species.

• The sense of smell is important for this form of communication.

Cleaning:

• Some tropical fish are cleaners. • They pick parasites from other fish. Cleaning

fish, such as wrasses, are brightly colored. • They establish cleaning stations that other fish

approach in order to be cleaned. • Body posturing, a form of visual

communication, is used to initiate cleaning.

Color

Red

• Red is a common color in fish. • You might think that red fish would be very

easy for a predator to find. • However, most fish that have this coloration

live in dark or deep water, or are nocturnal (active at night).

• In deep water, red light is filtered out quickly so red is a good camouflage.

• At night, red-colored objects appear gray.

Countershading

• Many fish are dark on top and light on the bottom.

• When seen from above they "disappear" by blending in with the dark color of the depths of the bottom.

• Seen from below, the light belly blends into the sky above.

Disruptive Coloration

• This is a form of camouflage. • The patterns and lines break up the outline of

the fish and help it to blend into the background.

• This confuses predators since the fish shape is not easily identifiable.

Eye Spots

• Eye spots are a form of mimicry. • They eye spot, usually found near the tail, may

be used to draw attention away from the real eye which is a target that a predator might strike.

Warning Coloration

• Many fish use bright colors to "advertise" the presence of venomous spines or some other defensive mechanism

Camouflage

• Many fish have colors or patterns that match their backgrounds.

• Some fish can even change color to match different backgrounds either to hide from prey (if an ambush is planned!) or to hide from a predator.

Food

• As a group, bony fishes have a diverse range of food preferences.

• They may be herbivores (plant-eaters), carnivores (meat-eaters), omnivores (plant- and meat-eaters) or detritivores (animals that eat decomposing plants and animals).

• Some of the animals common in the diets of bony fishes include worms, marine snails, mussels, clams, squids, crustaceans, insects, birds, amphibians, small mammals and other fishes.

• The amount of food a bony fish eats is directly related to its size, its metabolic rate and the temperature of its environment.

• Warm water fishes, such as tropical fish, generally have higher metabolic rates and require more food than coldwater species of the same size.

• The esophagus in bony fishes is short, expandable and layered with muscles so that large objects can be swallowed.

• Most species of bony fishes have a stomach with gastric glands that release substances that break down the food to prepare it for digestion.

• The intestine is where the majority of food absorption takes place and the digestive system terminates at the anus.

Reproduction in Fish

• In most species of bony fishes, sperm and eggs develop in separate male and female individuals.

• Fertilization is predominately external and, in some instances, internal.

• Males and females may look similar, or they may look very different.

• Male/female characteristics may include size, coloration, external reproductive organs, head characteristics and body shape.

• While reproduction in bony fishes is generally cyclic, various factors may influence bony fish breeding such as changes in the duration of sunlight, temperature changes, moon stages and presence of spawning areas.

• Bony fishes show at least three types of embryonic development: egg layers (oviparous), egg retainers (ovoviviparous) and live bearing (viviparous).

• Depending on the species, fish parents (male and/or female) may scatter, hide, guard or brood eggs.

• There is great variation in the development stage at which offspring are released from the parent fish.

• The number of offspring is inversely related to the chance a single egg has to reach maturity and reproduce; in general, species whose eggs have little chance to reach maturity lay the most eggs.

• For the most part, many species give no care to their eggs or young.

Figure 8.25

Fish Reproduction• Most Fish reproduce sexually, and

fertilize their eggs externally (Sharks-internally).

• Spawning is the process of fertilizing eggs.

• Baby fish are called FRY.

Fish Circulation

• Fish heart has 2 chambers• Single loop circulation

• Blood flows into gills, picks up O2, goes to the body, returns to the heart.

Fish Adaptations• Lateral Line System- used to detect

vibrations, orient the fish in water, it is a line of cells running down the side of the fish.

• Operculum- gill cover, movement of operculum allows more water to be drawn in.

• Swim Bladder- a gas filled sac that helps the fish maintain buoyancy. Sharks don’t have a swim bladder!

• Fins- Dorsal, Caudal, Pectoral, Pelvic, Anal.

Adaptations

Air Bladder Operculum Lateral Gills Line

Fins

Figure 8.02

Figure 8.16a

Figure 8.16b

Figure 8.17a

Figure 8.17b

Figure 8.17c

Figure 8.17d

Figure 8.17e

Figure 8.18a

Figure 8.18b

Figure 8.19

Figure 8.22

Figure 8.24

Figure 8.28