A、Because the fish population is increasing. B、Because the temperature there is increasing. C、Because the temperature there is d

Recently completed research reveals warmer oceans caused by global warming is making it more difficult for fish to breathe and survive.
    Biologists have known for years declining fish stocks arc connected to global warming, but a new study of eelpouts—big-headed fish that resemble eels—is the first to go deeper and see how warmer seas are connected to how fishes take in oxygen.
    Scientists studied the relationship between sea temperature and eelpouts counts in the Southern North Sea, combining data from the field with lab investigations of eelpout physiology.
    The researchers not only found the oxygen levels in the waters of the North and Baltic Seas have dropped because of increasing temperatures over the past 50 years--a factor that reduces fish population— they also discovered eelpouts need more oxygen in warmer waters, a second factor that is reducing their numbers.
    A key factor in the diminishing size offish stock is increased difficulty in absorbing oxygen via respiration and blood circulation caused by the warming waters.
    Animals tolerate a limited range of environmental conditions. Anything out of their tolerance can cause damage. Fish in the North Sea have evolved to tolerate a wider range of temperatures than fish elsewhere because of the large seasonal fluctuations there.
    Worldwide, warming waters can be expected to strain species that require lots of oxygen, forcing them to either relocate to cooler waters or face extinction.