What would happen if you put a freshwater gold fish into a 25% NaCl solution aquarium?

Question

You will need to be familiar with osmosis, hypertonic, isotonic, and hypotonic.

Answer 1

Hello!

Before we jump right in to the question, let's review what osmosis, hypertonicity, hypotonicity, and isotonicity mean in the context of our problem.

Osmosis describes the movement of water from an area with a lot of ions (higher concentration) to an area with fewer ions (lower concentration). Water wants to make the ratio of ions to water the same. For this problem, water will want to move in the direction of the solution with higher NaCl concentration.

Isotonic solutions are those that have the same concentration of ions as the target cell/organ/organism. Because isotonic solutions have equal concentration, water won't need to move anywhere to balance the concentration.

Hypertonic solutions are those with a higher concentration of ions compared to the target organism. Because they have a higher concentration than the target, water will want to flow from the target towards the hypertonic solution to balance the concentrations out. If we're talking about individual cells, the water rushing out of the cell by osmosis may cause the cell to shrivel up.

Hypotonic solutions are those with lower concentration of ions compared to the target organism. Because they have lower concentration than the target, water will want to flow towards the target from the hypotonic solution in order to balance the concentrations. In individual cells, if introduced to hypotonic solutions, water will rush into the cell by osmosis and may cause the cell to burst.

Now back to our problem: Is a 25% NaCl solution isotonic, hypertonic, or hypotonic?

For reference, 0.9% NaCl solutions are considered isotonic to human blood — so 25% NaCl is VERY salty! It is likely hypertonic to freshwater fish, who are used to swimming in water that doesn't have a lot of salt.

Because we know osmosis is the process by which water wants to move from less salty/concentrated to more salty/concentrated areas, we know that water will want to move from the fish to the solution.

Therefore, if placed in a 25% NaCl aquarium, a freshwater goldfish would likely lose water (become dehydrated).

Answer 2

I would be careful using the terms hypertonic and hypotonic here and specific percentages. The solute concentration in goldfish bodily fluids and cells is likely higher than freshwater, so there are various mechanisms to maintain osmotic balance. Without knowing more information, the correct way to respond would be that goldfish placed in a 25% NaCl solution will not be able to maintain osmotic balance, homeostasis, water will likely move out of cells at a higher rate and disrupt cellular and body functions.

Answer 3

Here we have a hypertonic solution (the environment concentration is higher) where the solute is present in greater quantity in the fluid outside the organism. This will lead to a net outflow of fluid toward the environment which means that the fish will get dehydrated and the cells will shrink.

Key points: In hypertonic solution, the fluid inside the cell flows outside the cell resulting in cell shrinkage. In hypotonic solution, the fluid flows into the cell leading to swelling of the cell. In isotonic solution, there is no net movement of fluid.

Answer 4

Follow the water! Osmosis is defined as the net movement of water molecules from an area of high water molecule concentration to an area of lower water molecule concentration. A goldfish is a freshwater fish living in an environment that is close to pure water, say 98% water. Therefore their cells will be about 98% water (isotonic to the pond they live in.) A 25% NaCl solution looks scary, but simply subtract 25 from 100 and you get 75% water (seawater is about 75% freshwater!) Now you know where the high and low water concentrations are located. The aquarium is a hypertonic environment. This means the water is higher inside the cells of the goldfish and will therefore rush out of the fish's cells causing crenation. Left unchecked, this would kill the fish!