1 . The skeleton of bony fishes is made of bone and cartilage.
2. The skeleton of a bony fish gives structure, provides protection, assists in leverage, and is a site of red blood cell production.
3. Bony fishes have skeletons that are almost completely calcified. The vertebral column, cranium, jaw, ribs, and intramuscular bones make up the bony fish skeleton.
The vertebral column, cranium, jaw, ribs, and intramuscular bones make up
the bony fish skeleton.
1 Tail and trunk muscles.
a. The muscles of the tail and trunk consist of a series of muscle blocks called myotomes. The myotomes usually resemble the letter "W" tipped at a 900' angle.
b. The myotomes are separated by connective tissue called myosepta.
c. The horizontal septum separates the myotomes into dorsal (or epaxial) myotomes and ventral (or hypaxial) myotomes.
Muscle blocks called myotomes are separated by connective tissue called
myosepta.
2. Jaw muscles.
Jaw muscles usually consist of adductor muscles that close the jaw and abductor muscles that open the jaw.
3. Fin muscles.
The fin muscles consist of abductor and adductor muscles that move the fins away from and close to the body, and erector muscles that provide stability and flexibility in the fins.
1 . The nervous system of fishes is poorly developed compared to that of higher vertebrates.
2. A bony fish's brain is divided into three sections: the forebrain, the midbrain, and the hindbrain.
a. The forebrain is responsible for the bony fish's ability to smell. Bony fishes that have a good sense of smell, such as eels, have an enlarged forebrain (Bond,1979).
b. The midbrain is responsible for vision, learning, and motor responses. Blind bony fishes, such as blind cavefishes (family Amblyopsidae), have a reduced midbrain (Bond, 1979).
c. The hindbrain contains the medulla oblongala and cerebellum, which coordinates movement, muscle tone, and balance. Fast-swimming bony fishes usually have an enlarged hindbrain (Bond, 1979).
3. The spinal cord and a matrix of nerves serve the rest of the body.
1 . Bony fishes have a heart with two chambers: the atrium and the ventricle. The venous side of the heart is preceded by an enlarged chamber called the sinus venosus. The arterial side of the heart is followed by a thickened muscular cavity called the bulbus arteriosus.
a. The sinus venosus receives unoxygenated blood from the body. A valve at the end of the sinus venosus opens into the atrium.
b. The atrium has thick, muscular walls. The atrium receives unoxygenated blood and pumps it into the ventricle.
c. The ventricle is the largest and most muscular chamber of the heart. When the ventricle fills with blood it constricts and forces the blood through the bulbus arteriosus.
d. The bulbus arteriosus is a valve or series of valves that control blood flow out of the ventricle and into the ventral aorta. Blood passes through the bulbus arteriosus to the ventral aorta. From the ventral aorta, blood flows to the gill filaments, where it is oxygenated.
e. The spleen, kidney, and bones are sites of red blood cell production.
2. Oxygenated blood flows from the gill filaments to the organs of the head and body. A complex system of arteries, veins, and capillaries circulates blood through the body.
3. Some tunas (family Scombridae, tribe Thunnini) maintain a body temperature several degrees higher than that of the surrounding water. This heat is due to the modified circulatory system associated with the red muscle.
a. As red muscle functions, it generates heat. Muscle-generated heat warms the blood circulating through the red muscle, which then travels back to the heart through veins. Thus, blood returning to the heart from the muscle is warmer than blood traveling from the heart to the muscle.
b. Due to the nearness of arteries and veins, heat passes from warmer veins to cooler arteries within the fish's body, rather than dissipating to the cooler environment. This modified circulatory system retains heat in the red muscle.
c. A higher body temperature is an adaptive advantage in that it provides extra power for high-speed swimming.
d. A similar modified circulatory system warms the brain and eye of some species of tunas (family Scombridae, tribe Thunnini) and billfishes (family lstiophoridae).
1 . The esophagus in bony fishes is short and expandable so that large objects can be swallowed. The esophagus walls are layered with muscle.
2. Most species of bony fishes have a stomach. Usually the stomach is a bent muscular tube in a "U" or "V" shape. Gastric glands release substances that break down the food to prepare it for digestion.
3. At the end of the stomach, many bony fishes have blind sacs called pyloric caeca. Although the exact function of the pyloric caeca is unknown, it probably functions both in digestion and absorption of food.
4. The pancreas secretes enzymes into the intestine for digestion.
5. The intestine is where the majority of food absorption takes place. The length of the intestine in bony fishes varies greatly. Herbivorous bony fishes generally have long, coiled intestines, and carnivorous bony fishes have short intestines.
6. The digestive system terminates at the anus.
1 . Water enters the gill chamber through the mouth. A bony fish can remain motionless and breathe by pumping water over its gills by opening and closing its mouth.
2. Blood in the gill filaments absorbs oxygen from the incoming water.
3. Water exits through the gill openings located under the operculum.
4. Lungfish must return to the surface to breathe air. A lungfish swallows air to fill up an air sac or "lung." This lung is surrounded by veins that bring blood to be oxygenated. Its gills alone can't keep a lungfish supplied with enough oxygen to live. Other species such as tarpon (family Elopidae) can gulp air at the surface to supplement their oxygen demand.
5. Some species of bony fishes can absorb considerable amounts of oxygen through their skin (Bond, 1979).
1 . Many species of bony fishes have a gas-filled bladder called a swim bladder.
2. The swim bladder originally developed as an organ of respiration, as evidenced by the "lung" of the lungfishes.
3. In modern bony fishes that possess a swim bladder, the organ serves principally in maintaining neutral buoyancy. 4. In some fishes the swim bladder has adapted to function as a sound amplifier.
1. Both marine and freshwater fishes must regulate the movement of water across their body surfaces.
2. The tissues of marine fishes are less salty than the surrounding water.
a. Water is continually leaving the body of a marine fish through its skin and gills.
b. To keep from becoming dehydrated, a marine fish drinks large amounts of water and produces a small amount of concentrated urine. In addition, its gills are adapted to secrete salt.
3. The tissues of a freshwater fish are saltier than its surrounding environment.
a. Water is continually entering the body of a freshwater fish through its skin and gills.
b. Freshwater fishes do not drink water, and they produce large amounts of dilute urine.
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