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Osmoregulation in Fish

Preparation By Mandeep Poonia MSc. Final(14042001), GJU S&T Hisar(Haryana)-India

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Please listen and understand carefully bcoz at the end of

Presentation there are some questions related to what you

have learned

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Let’s first know about Osmoregulation

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What is Osmosis

The net movement of solvent molecules from a region of high solvent potential to a region of lower solvent potential through a partially permeable membrane.

OrOsmosis is defined as the flow of water/solvent molecules through a semi-

permeable membrane from a region of low solute cocentration to a region of high solute concentration, until equilibrium is established.

OrOsmosis is the diffusion of a fluid through a semi-permeable membrane. When a

semi-permeable membrane (i.e. skins of fruits and vegetables) separates a solution from a solvent, then only solvent molecules are able to pass through the membrane.

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What is Osmotic Pressure

The osmotic pressure of a solution is the pressure difference needed to stop the flow of solvent across a semi-permeable membrane.

orTo stop osmotic flow, some pressure must be applied to

the solution in order to prevent pure solvent from going through the semi-permeable membrane separating the two liquids; this is known as the osmotic pressure.

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Osmoregulation

Osmoregulation means the physiological processes that an organism uses to maintain water balance

It is used to compensate for water loss, avoid excess water gain, and maintain the proper osmotic concentration of the body fluids.

Most humans are about 55 to 60 percent water by weight (45 percent in elderly and up to 75 percent in newborn infants). Many jellyfish are 95 percent or more water.

Thus the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt concentrations is Known as Osmoregulation.

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Now we come toOsmo-regulation

in

Fish

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Now before discussing the main articlewe try to understand the different

parts of fish

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Because of their environment, osmoregulation in fish presents specific problems.

Fish have adaptations that enable them to deal with these problems.

Those which live in fresh water or sea water have different problems.

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1. FRESHWATER FISHProblems:• These fish are hypertonic to their surroundings.

This means their blood has a lower water concentration than the surrounding fresh water.

• As fresh water passes through the mouth and over the gill membranes, water molecules diffuse from the fresh water into the blood by osmosis.

• These fish must produce a very large volume of urine to balance this large intake of water.

• This large volume of urine carries salt with it, and the salt has to be replaced.

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Solutions by fresh water fish:

• To produce a large volume of urine the fish must remove a large volume of water from the blood by having a high rate of filtration into the kidney tubules.

• This is done by having a kidney with many large glomeruli - capillary networks from which fluid is filtered at the start of the kidney tubules.

• Salt replacement is solved by chloride secretory cells in the gills, which actively transport salts from the surrounding water into the blood.

21Movement of water and ions in freshwater fish

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2. SALTWATER FISHProblems:• These fish are hypotonic to their surroundings. This means

their blood has a higher water concentration than the surrounding sea water.

• As sea water passes through the mouth and over the gill membranes, water molecules diffuse out of the blood into the sea water by osmosis.

• These fish must replace the water which they constantly lose by osmosis

• They can also only afford to produce a very small volume of urine.

• Drinking sea water brings a large quantity of salt into the blood and this has to be removed.

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Solutions by seawater fish :

• To replace the water they lose, saltwater fish drink sea water.

• To produce a small a volume of urine they must have a low rate of filtration of water into the kidney tubules.

• This is done by having a kidney with relatively few small glomeruli.

• Salt is removed by chloride secretory cells in the gills, which actively transport salts from the blood into the surrounding water.

24Movement of water and ions in sea water fish

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Let’s explain it little more

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Now we again discuss diffusion,

equilibrium, osmosis,

osmotic pressure and osmo-regulation in fish

with a different approach

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Diffusion and Equilibrium

Diffusion is simply the tendency of molecules to passively move from an area where they are more highly concentrated to an area where they are at a lower concentration - as a result of random movement.

Note here, that it is the molecules as a whole which move from higher to lower areas of concentration.

There will be a net movement of molecules down the concentration gradient until a point of equilibrium is reached.

At this point, the molecules are moving at equal rates up and down the concentration gradient and there is no further net movement of the particles.

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Diffusion and equilibrium can be illustrated by :

placing a drop of methylene blue in a glass of water. One will observe that after some time has passed, this dye has dispersed throughout the water until an even color can be observed in all areas. The dye molecules diffused through the water randomly and reached a point of equilibrium such that there is no further net color change in the glass.

In a different scenario, one can imagine being in a large room where someone lights a cigarette. At first only the people nearest to the cigarette will smell the smoke. However, after some time, everyone in the room will smell it. When the cigarette is no longer burning, the scent will be evenly detectable throughout the room as the smoke molecules diffuse and reach equilibrium.

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Osmosis

• Osmosis is a concept similar to diffusion which involves the passive movement of water through a membrane which is permeable to the water, but not to the solutes dissolved in the water.

• With osmosis, the water moves from an area of lower solute concentration to an area of higher solute concentration.

• While this may initially seem to be the opposite of diffusion, one must consider that the water is still moving from where the water is most abundant to where it is least abundant. This is illustrated in the figure below.

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Osmosis and osomotic PressureThe figure illustrates two U-shaped tubes,each of which contain two different salt solutions separated by a semi-permeable membrane which allows only water to pass through it In Tube A, the left side contains a hypertonic solution – having a higher concentration of solutes, and the right side contains a hypotonic solution, having a lower concentration of solutes.

Isotonic is a term for solutions of equal solute concentration.

Water moves from the hypotonic side to the hypertonic side and in doing so, increases the salt concentration on the right side of the tube and decreases the salt concentration on the left side of the tube until the two concentrations are equal.

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Osmotic pressure and equilibrium

• Tube B illustrates equilibrium. At equilibrium water is moving though the membrane in both directions at an equal rate.

• The pressure needed to stop the water level from rising on the left side of the tube is called the "osmotic pressure".

• Water always has a net movement toward the solution of higher osmotic pressure.

• At equilibrium, both sides of the tube have equal osmotic pressures.

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Solution effect on cell

A cell placed into a hypotonic solution will have water rush inside of it (where solutes are more concentrated) and cause the cell to burst.

A cell placed into a hypertonic solution will experience dehydration as water leaves the cell for the surrounding environment.

A cell placed into an isotonic solution will experience water entering the cell at the same rate at which it leaves, and so will be at equilibrium and appear normal.

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Osmoregulation in fish (freshwater)

• Fish do not always find themselves in isotonic environments.

• Thus, their body cells must have a means by which to adapt to changing salt concentrations in their bodies and environments.

• Osmoregulation controls this balance of water/salt concentrations.

• Freshwater fish are hypertonic to their water environment and therefore, water is continually diffusing into the fish through the gill membranes into the blood.

• The gills are also permeable to respiratory gases, ammonia waste products, and ions.

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Movement of ions and water in freshwater fish

Therefore, while water moves in towards the higher osmotic pressure of the blood, sodium and chloride ions also diffuse out of the fish, moving down their concentration gradients to the external environment.

Freshwater fish must expend energy to regulate this ion loss and fluid uptake.

Marine fish experience the opposite situation as their bodies are hypotonic to their saltwater environment.

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Role of Kidneys and Gills• The continual uptake of water in freshwater species is

regulated by the kidneys which continually produce large amounts of dilute urine.

• Despite the importance of healthy kidneys to help counteract the problem of taking on water, some salts are also lost in the large amounts of urine as well as through the membrane of the gills.

• Fortunately, the gills are also a site of ion uptake. Special cells in gill contain sodium and chloride "pumps". These pumps are special enzymes that use energy to move the ions up their concentration gradient (remember that moving down a concentration gradient is spontaneous, as in diffusion, and requires no input of energy) to maintain their higher concentration in the body.

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Importance of Osmoregulation

• Thus, osmoregulation is a process that requires the expenditure of much energy on the part of the fish--even when they appear to be inactive.

• This constant expenditure of energy to maintain an osmotic balance is a reason why proper nutrition and low stress levels are important for healthy fish.

• Damage to the kidneys through bacterial infection or other means is often deadly as these organs extract the large amounts of water which continually diffuse into the fish's body.

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Fishes with strong osmoregulation

• Angelfish and discus are examples of fish that have very strong and efficient osmoregulatory systems.

• They do well naturally in their native environment where the osmotic pressure is great due to the extremely soft water of the Amazon river basin.

• However, when under stress, these systems can be impaired.

• This is why it is advised to add some salt to the water of fish under stress. The salt reduces the osmotic pressure.

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Why osmoregulation in fish is more important

• A sudden change in osmotic pressure can put great stress on the osmoregulatory system of a fish.

• This is of great concern when shipping fish to locations with water different from what they're adapted to.

• The fish arrives under great stress and is not able to regulate any osmotic pressure differences easily.

• This fact also highlights the effect of polluted water over different water organisms.

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Angelfish

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Discus Fish

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Now it is the time to know what you have

understand

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Question 1

• is the diffusion of a fluid through a semi-permeable membrane.

Question 2• The of a solution is the

pressure difference needed to stop the flow of solvent across a semi-permeable membrane

Question 3• The maintenance of constant osmotic pressure

in the fluids of an organism by the control of water and salt concentrations is Known as .

OSMOSIS

OSMOTIC PRESSURE

OSMOREGULATION

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Question 4• The molecules as a whole when move from

higher to lower areas of concentration, the process is known as .

Question 5• There will be a net movement of molecules

down the concentration gradient until a point of is reached.

Question 6• The solution having a higher concentration of

solutes is known as ____________ solution

diffusion

equilibrium

hypertonic

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Question 7• The solution having a lower concentration of

solutes is known as ___________ solutionQuestion 8

• ____________ is a term for solutions of equal solute concentration

Question 9• Water always has a net movement toward the

solution of _________ osmotic pressure

hypotonic

Isotonic

higher

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Question 10• Freshwater fish are hypertonic to their

surroundings. This means their blood has a __________ water concentration than the surrounding fresh water

Question 11• Seawater fish are hypotonic to their

surroundings. This means their blood has a __________ water concentration than the surrounding sea water

lower

higher

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