A data logger is an electronic device that records data over time from sensors. It samples and saves data at predetermined frequencies. Data loggers are battery powered and can record without a computer. They are used to monitor conditions remotely like temperature or flow rate. The recorded data can then be downloaded to a PC for analysis. A swim bladder helps fish control buoyancy and maintain neutral density in water. It contains gas that can be adjusted to match the water's density to avoid energy expenditure swimming up or down. An experiment showed swim bladders demonstrate osmotic properties as pressure increased inside bladders in a sucrose solution, supporting their selective permeability.