Fish Comparative Anatomy: Questions for Discussion 1. What structures play a rol
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Fish Comparative Anatomy: Questions for Discussion 1. What structures play a role in buoyancy and the generation of lift in cartilaginous fishes? In bony fishes? What advantages does the bony fish strategy have over the cartilaginous fish strategy? Are there any disadvantages to the bony fish strategy? 2. What fins are present on each of the fish that have been dissected? What are the functions of the various fins these fishes? Are the functions the same in both groups? 3. One of the trends observed in the evolution of vertebrate digestive systems is arn increase in the efficiency of nutrient extraction from food. What anatomical features o the shark digestive system reflect this trend? 4. One significant structure that is present in bony fish, but absent in jawless and cartilaginous fishes, is the operculum. What is the function of the op is it considered an evolutionary advancement? erculum and why 5. Describe the respiratory and circulatory systems of cartilaginous and bony fishesExplanation / Answer
1) Bony fish achieve neutral buoyancy through an air filled sac called the swim bladder. The swim bladder controls the fish’s buoyancy by varying the gas pressure inside the fish’s body to allow it to sink or rise in the water.”
Cartilaginous fish (sharks, rays) do not have swim bladders. Instead, they achieve neutral buoyancy by...
Storing lipids throughout their body.
Reduction of blubber.
Dynamic lift.
Sharks generate lift with their swimming motion. (This is why a shark’s fin is so important to a shark. They need it to swim)
Modern sharks most likely evolved their lighter cartilaginous skeletons to become faster swimmers, to evade predators and swiftly catch their prey. The loss of bone in their skeleton is also supported by the fact the oldest and most basal of all jawed vertebrates, the placoderms, had heavy bony skeletons. In the most recent phylogenetic analysis of lower vertebrates, the placoderms appear as being basal – or at a common evolutionary level – to sharks.
2)
3) Most sharks swallow their food whole or bite it into relatively large pieces. Sharks have U-shaped stomachs that use very strong acids and enzymes to dissolve most of what is eaten. The stomach produces an easily absorbed, soupy mush. Only this liquid mush enters the intestines because the pyloric valve (the valve between the stomach and the intestines) is small. Indigestible things, (like very large bones and non-nutritive items) are vomited.
Absorption of nutrients takes place in the intestines. Although the intestines are short, they have a large surface area due to infolding of the inner surface of the intestines. Some shark intestines are arranged in folds, some are in a spiral pattern, like a spiral staircase enclosed within a cylinder.
4) The operculum is a series of bones found in bony fish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding.
The opercular series contains four bone segments known as the preoperculum, suboperculum, interoperculum and operculum. The preoperculum is a crescent-shaped structure that has a series of ridges directed posterodorsally to the organisms canal pores. The preoperculum can be located through an exposed condyle that is present immediately under its ventral margin; it also borders the operculum, suboperculum, and interoperculum posteriorly. The suboperculum is rectangular in shape in most bony fishy and is located ventral to the preoperculum and operculum components. It is the thinnest bone segment out of the opercular series and is located directly above the gills. The interoperculum is triangular shaped and borders the suboperculum posterodorsally and the preoperculum anterodorsally. This bone is also known to be short on the dorsal and ventral surrounding borders.
During development the opercular series is known to be one of the first bone structures to form. In the three-spined stickleback the opercular series is seen forming at around seven days after fertilization. Within hours the formation of the shape is visible and then the individual components are developed days later. The size and shape of the operculum bone is dependent on the organism's location. For example, fresh water threespine sticklebacks form a less dense and smaller opercular series in relation to marine threespine sticklebacks. The marine threespine stickleback exhibits a larger and thicker opercular series. This provides evidence that there was an evolutionary change in the operculum bone. The thicker and more dense bone may have been favored due to selective pressures exerted from the threespine stickleback's environment. The development of the operculuar series has changed dramatically over time. The fossil record of the threespine stickleback provide the ancestral shapes of the operculum bone. Overall, the operculum bone became more triangular in shape and thicker in size over time.
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