Final answer:
Fishes regulate the gas content and pressure of the swim bladder to control buoyancy. They adjust the gas content by secreting or absorbing gases from the bloodstream and control the pressure by changing the volume of gas in the swim bladder. So, the correct answer is option a.
Step-by-step explanation:
Fishes control the gas content and pressure of the swim bladder in various ways. They adjust the gas content of the swim bladder by secreting gases into or absorbing gases from the bloodstream. This allows them to maintain appropriate buoyancy.
Additionally, fishes control the pressure by altering the volume of gas in the swim bladder, compressing or expanding it as needed. The swim bladder is not directly connected to the bloodstream for continuous regulation of gas composition and pressure.
So, the correct answer is option a.