Welcome to Daily Bitachon. We are now in our Sha'ar HaBechina series, finding oneness in creation, and today we are talking in general about what the Chovot HaLevavot calls the swimmers. The Physics of Buoyancy Aquatic creatures face a very interesting challenge: maintaining a specific depth without constantly exerting energy to keep from sinking or floating away. So, how do they maintain that stability? We have a wonder called the swim bladder. The Engineering: Most bony fish possess a gas-filled sac called a swim bladder. By adjusting the amount of gas inside this organ, a fish can achieve neutral buoyancy, effectively becoming weightless at any depth. Now, you could try this yourself; I learned this in camp. The best way, if you are stuck in the ocean and don't want to exert energy swimming, is to tilt yourself backwards and take a deep breath. Your lungs will fill with oxygen, creating your own little "swim bladder." That will keep you exactly above water. You hold your breath for thirty or forty seconds, then take another deep breath and just lean your shoulders back, and you have a way to stay afloat without swimming. Now, why they taught us that in camp—what the odds are you'll be stuck in the middle of the ocean—I don't know, but every once in a while, when I'm swimming in the pool, I'll do that. It's just fun. You relax and fill up the air in your lungs, so we also have that option. However, since the fish's organ is designed by Hashem specifically for this, it has certain chemicals that make it gas-tight, and it's positioned near the spine, which places the fish's center at the exact spot of buoyancy. Like I said, a person's lungs are not made for that; they aren't in the center, and therefore it doesn't quite keep you steady—your legs still dangle. Everything in human technology is just mimicking what God put into the wisdom of creation. Just as a submarine has ballast tanks, the fish maintains its upright and stable position automatically, remaining perfectly still in the water while waiting for prey or resting. Oxygen Extraction: The Counter-Current System The next big challenge is: how do you get oxygen out of the water? It is much easier to get oxygen out of air than out of water. Water is much denser and contains significantly less oxygen than the atmosphere. Inside a fish's gills, blood flows in the opposite direction to the water flowing over them. This is known as a counter-current exchange system. This arrangement ensures that the oxygen-poor blood always encounters oxygen-rich water along the entire length of the gill. If the blood flowed in the same direction as the water, the fish could only extract about fifty percent of the oxygen. With this reverse-flow design, a fish can extract up to eighty to ninety percent of the oxygen from the water. Navigation and Senses Another interesting thing about fish is their ability to migrate. We all know about the salmon that spends years in the open ocean, traveling thousands of miles, yet returns to the exact same stream where it was born to procreate. How do they do this? Magnetic Compass: Like birds, they have tiny crystals of magnetite in their brains that allow them to sense the Earth's magnetic field, acting as a compass. Wonder of wonders! Chemical Signature: As they get close to land, they use their incredibly sensitive sense of smell to detect the unique chemical signature of their home river, which they imprinted on themselves when they were just little baby fish. This is God's "programmed genius," what we call instinct. No human could find their way across an ocean to a specific backyard creek without a map and a satellite, yet the fish does it with a brain the size of a pea. Finally, how do you see through water? Light does not travel far in water, and it's pretty dark down there. So, fish have a sense that humans do not possess. Running down the side of a fish's body is a series of fluid-filled canals containing sensory hairs called the lateral line . This system allows the fish to detect minute pressure waves in the water. It can feel the movement of a predator or the vibration of prey from a distance, even in total darkness. They aren't just seeing; they are sensing vibrations. This is effectively "touch at a distance," allowing fish to swim in massive, tight schools without ever colliding, as each fish feels the pressure change of its neighbor instantly. These are the general points of wisdom regarding fish before we go into the specifics.