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BONY FISH!Osteichthyes!

Bony Fish!

!  There are about 24,000 species of bony fish. Bony fish have thin, flexible overlapping scales and a flap of bone that covers the gills called a gill cover or operculum. Both lobes of the tail are usually the same size and the mouth usually ends at the anterior end of the animal, unlike a shark, where the mouth is usually on the bottom surface of the body.

Scales and Tails! Bony Fish!

!  The mouth usually has more movement than in sharks and the teeth are fused to the jawbone Most bony fishes have a gas filled sac called a swim bladder. This allows the fish to adjust buoyancy to either float of sink.

Body Shape!

!  The body shape is related to the environment the fish lives and swims in. Fast swimming fish like the tuna have a streamlined body, while snappers have laterally compressed bodies suited for swimming in between coral reefs, kelp beds or rocky shores. This flattened body still allows for shore bursts of speed when necessary. !

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• Flounders and fluke live on the bottom and have flattened bodies and some eel-like fishes have narrow long bodies to move in and out of small spaces with in rock or coral structures. !

Flat Body Shape! Coloration!

!   Some fish use color to blend in with the background to camouflage themselves against predators. The special cells within the skin that have the colored pigments are called chromatophores. !

Coloration!

• Some will use color as a warning called warning coloration, which could say they are poisonous or taste bad. Cryptic coloration is the ability to blend in with the surroundings for camouflage. Open water fish will have countershading, which is a white bottom and a dark colored top.!

Countershading! Warning Coloration!

Locomotion!!  Swimming is a major part of a fish’s life. They

will swim to obtain food, get oxygen as well as escape predators. Most fish swim with a rhythmic side-to-side motion using the tail. This side-to-side motion is created using special band of muscles called myomeres. Muscles in fish can make up as much as 75% of the body weight. !

Obtain Oxygen! Deep Red Color Muscles!

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Staying Afloat!

• Bony fish use the swim bladder to help float but sharks don’t have that. They have a very oily liver and large pectoral fins to provide lift. Because fish don’t need the pectoral fins to stay afloat, they can use them for maneuverability and even swim backwards. The dorsal and anal fins are employed as rudders and can help steer the fish.!

Other Types of Locomotion!

!  Some fish use their pectoral fins to “crawl” along the bottom, while others like the flying fish use their pectoral fins to glide on the air. Other adaptations are to hold on like clingfish that will attach to rocks and remoras or sharksuckers that will attach to sharks, whales and turtles.!

Feeding!

!  Many fish are carnivores and will swallow small prey whole. Sharks on the other hand have the ability to bite off pieces of animals that are larger than they are. Sharks are not particular either, because a tiger shark was caught off of South Africa and in its stomach was half of a crocodile, the hind legs of a sheep, three gulls and two cans of peas.!

• Not all sharks are vicious killers. Nurse sharks live near the bottom and feed primarily on bottom invertebrates while the whale shark is a filter feeder. There are three specifies of filter feeding sharks and they all have adaptation to the gills called gill rakers that clean the gills and swallow the food caught in them.!

Feeding!

!  Bony fishes are very diverse in the way they feed. Most are carnivorous and will either chase their prey, eat it off the bottom or sit and wait for it. Their teeth are designed to hold the food and then swallow it whole. Deep-water fish usually have large mouths in order to capture and eat food larger than they are.!

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• Fish that feed on seaweed are known as grazers and some fish will filter feed using their gill rakers to clean the gills and eat the food. They are usually found in enormous schools and are an important food source for many marine organisms.!

Digestion!

• After being swallowed the food passes down an esophagus and into the stomach then into the intestines. A fish has digestive enzymes that help to break down the food it ingests. The blood takes up the nutrients and the undigested food passes out through the anus.!

Circulatory System!

!  All fishes have a two-chambered heart. Deoxygenated blood comes in from the body in the veins and pumped to the gills where gas exchange takes place. The oxygenated blood is returned to the body through arteries and capillaries.

Respiration!!   Fish obtain dissolved oxygen from the water in the gills as

the water passes called irrigation. Cartilaginous fishes open their mouth and force the water over the gills that have their own chamber that opens to the outside by gill slits.!

• Bony fishes have a more efficient mechanism to bring in water. They have only one gill opening and when the mouth opens the operculum closes and the pharynx expands and pumps the water out by closing the mouth and reversing the process. If the fish is a fast swimmer, it only has to open the mouth.!

Operculum! Gill Structure!• The gills are supported by a cartilaginous or bony

structure called a gill arch. Each arch bears two rows of gill filaments. Gill rakers are there to protect the gills and clean food particles and other materials from them when necessary. Each gill filament contains many rows of thin plates or discs called lamellae, which are rich in capillaries that give them the red color, and are where the gas exchange takes place.!

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• Once the oxygen reaches the blood, hemoglobin on the red blood cells transport the oxygen where it needs to go. Muscles that use a lot of oxygen during exertion have a protein called myoglobin, similar to hemoglobin that has the ability to store oxygen. Fast swimming fish like tuna and sharks have a large concentration of red muscle as opposed to white muscle like many of the fish you like to eat. Many other fish have this red muscle at the base of the heavily used swimming fins.!

Regulation of Internal Environment!

!  The blood of marine fish is less salty than the ocean water so they lose a lot of water through osmosis. They replace the water by drinking it and excreting the extra salt in a concentrated urine or by special cells in the gills called chloride cells. This goes to show that the kidneys are the most important organs in a marine fish.!

• In cartilaginous fishes they reduce osmosis by increasing the amount of dissolved molecules inside the body. They do this by retaining the urea, the waste produce of protein breakdown controlled by the kidneys. Cartilaginous fish can also absorb water through the gills and excrete the extra salt through the kidneys and special cells near the anus.!

Nervous System and Sensory Organs!

!   Marine fishes have a central nervous system with a brain, spinal cord and nerves. Most fish have a highly developed sense of smell used to detect food, predators and mates. The sensory cells are called olfactory sacs and are located on both sides of the head.!

!   Bony fish will also use their eyes to see food and predators. In order to protect the eyes of sharks in times of high light or attack, a nictitating membrane can close.!

• Cartilaginous fish also have sense organs called Ampullae of Lorenzini that can detect weak electrical fields. They also have inner ears with fluid filled canals that have the ability to perceive sound waves and help in balance.!

Behavior !

!  Many open water fish simply swim around but fish that live in smaller areas will establish territories and will defend them if necessary. Some fish will use sound by gritting their teeth or rubbing the bones or fin spine together to show territoriality.!

• Many fish will form well-defined groups called schools. The fish are usually the same size and makes the whole appear large. The fish are able to keep a constant space between each other. This can be advantageous as well as not. Killer whales and tuna will use the school as a large table with unlimited food.!

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Schooling Fish! Reproduction and Life History!

!  Reproduction is simple and involves a pair of gonads that produce either sperm or eggs. Fertilization is external and the female will lay thousands of eggs and the male will fertilize them. The timing of reproduction is controlled by sex hormones and is triggered by day length, temperature or availability of food.!

• Few marine fish are hermaphrodites. Some however can change sex from either male to female or female to male all controlled by sex hormones. Sea basses and groupers are examples of fish that can do this.!

Courtship!

!  Potential mates must get together at the right time to breed. Some fish will change color when they are ready and some sharks will come together only during breeding season.!

• Courtship is a series of behaviors that server to attract the male or female depending on the species. Some will dance or swim in a special pattern in order to attract the other. External fertilization is the norm in bony fish but internal fertilization is commonly seen in cartilaginous fish like sharks. Male sharks will use claspers and insert them into the female’s cloaca. He will usually bite her to hang on.!

Fin Damaged From Mating!

!  Most fish spawn eggs that are known as oviparous. In oviparous sharks, skates and rays the embryo is enclosed in a large leathery egg case that drops to the bottom. The eggs have extensions on either side to attach to things and only a few are laid at a time. The eggs have a large amount of yolk in a yolk sac that is attached to embryo’s belly.!

!   Some cartilaginous fishes are ovoviviparous, which means the egg develops in the female and a live young is produced. Some ovoviviparous sharks have only two young, because they used up the yolk and have eaten all of the other brothers and sisters. Only one is born on each side of the mother’s reproductive tract.!

!   A small number of sharks and rays are viviparous, which means the embryo absorbs nutrients from the mother like in mammals.!

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Development!

!  In most bony fishes the development is much quicker. The egg is thin and has the ability to absorb oxygen from the seawater. The embryo is supplied with nutrients from the yolk and after a few days a free-swimming larva emerges. Sometimes the larva looks nothing like the parent and will undergo a metamorphosis.!