They use a internal pouch which is named swim bladder.
Explanation; Oxygen will enter a fish’s mouth, and passes through their gills. The oxygen will be taken and gets carried by hemoglobin through their bloodstream. Hemoglobin will take out some of the oxygen into their swim bladder. The amount of oxygen will show if they will sink or rise. Your question is how do they rise. If he goes up too much, the meaning of this is when the gas diffuses into their blood and out the gills.
Got this from a writing, but rephrased it.
The rapid depolarization phase of the action potentials of myocardial contractile cells is due to Na⁺ ion.
The depolarization is caused when Na⁺ ions rapidly enters into neuron through open sodium channels. Sodium ions plays important role in various physiological process such as regulating blood volume, ph regulation, maintaining blood pressure, energy metabolism,osmotic equilibrium, excitation-contraction coupling, maintenance of cellular homeostasis, development and growth.
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The Answer is B, or the 2nd one since it starts from one cell and splits into 2 meaning it's under going mitosis.