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Questions and Answers
What is the primary function of the salt-absorbing cells in the gill epithelium of freshwater fishes?
What is the primary function of the salt-absorbing cells in the gill epithelium of freshwater fishes?
What is the main difference in salt concentration between freshwater and the blood of freshwater fishes?
What is the main difference in salt concentration between freshwater and the blood of freshwater fishes?
What percentage of all bony fishes are restricted to either a freshwater or a seawater habitat?
What percentage of all bony fishes are restricted to either a freshwater or a seawater habitat?
What is the term used to describe fishes that can pass back and forth between freshwater and seawater habitats?
What is the term used to describe fishes that can pass back and forth between freshwater and seawater habitats?
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What is the primary function of the opisthonephric kidneys in freshwater fishes?
What is the primary function of the opisthonephric kidneys in freshwater fishes?
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What is the main function of the operculum in fish?
What is the main function of the operculum in fish?
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Which type of fish can remove as much as 85% of the dissolved oxygen from water passing over their gills?
Which type of fish can remove as much as 85% of the dissolved oxygen from water passing over their gills?
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What is the term for the process by which fish swim forward continuously to force water into their open mouth and across their gills?
What is the term for the process by which fish swim forward continuously to force water into their open mouth and across their gills?
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What is the main respiratory surface used by freshwater eels during overland excursions?
What is the main respiratory surface used by freshwater eels during overland excursions?
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Which type of fish have a series of gill slits instead of opercular flaps?
Which type of fish have a series of gill slits instead of opercular flaps?
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Study Notes
Respiration in Fish
- Fish gills are composed of thin filaments with a thin epidermal membrane folded into platelike lamellae, richly supplied with blood vessels.
- Gills are located inside the pharyngeal cavity and are covered with a movable flap, the operculum, which provides protection and enables a pumping system for moving water.
- In elasmobranchs, gill slits replace opercular flaps, and water flows out of these slits.
- The branchial mechanism is arranged to pump water continuously and smoothly over the gills, with a countercurrent flow that maximizes oxygen extraction from water.
- Some bony fishes can remove up to 85% of dissolved oxygen from water passing over their gills.
- Very active fishes, such as herring and mackerel, use ram ventilation, swimming forward continuously to force water into their open mouth and across their gills.
- Some fishes can live out of water for varying lengths of time by breathing air, using devices such as lungs, skin, and air chambers.
Osmotic Regulation in Fish
- Freshwater is a dilute medium with a salt concentration much below that of the blood of freshwater fishes.
- Water tends to enter the body osmotically, and salt is lost by diffusion outward across the gills.
- Freshwater fishes are hyperosmotic regulators with defenses against water gain and salt loss, including:
- Excess water pumped out by the opisthonephric kidneys.
- Special salt-absorbing cells in the gill epithelium that actively move salt ions from water to the blood.
- These mechanisms allow freshwater fishes to devote only a small part of their total energy to maintaining osmotic balance.
- About 90% of bony fishes are restricted to either a freshwater or a seawater habitat because they are incapable of osmotic regulation in the "wrong" habitat.
- However, some 10% of teleosts are euryhaline, capable of passing between freshwater and seawater habitats with ease.
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Description
This quiz covers the structure and function of fish gills, including the composition of filaments and lamellae, blood supply, and the role of the operculum in facilitating respiration.
