Fishes are very sensitive to their surroundings. The body temperature of fishes is controlled by the water temperature. The temperature of ocean is increasing every year. And that excess heat in the water will bring biological changes in fishes. Their behavior will change to adapt with the rising temperature of the ocean water. Their reproduction behavior, swimming ability and growth will be affected by the excess heat in the ocean water. For reproduction activity fishes need a certain range of temperature in the right time. Slight increase of the ocean water temperature will affect their reproduction process in a great scale. Beside the ocean water temperature is also very important to determine the sex of fishes. So the population of certain fishes highly depends on the ocean water temperature.

Ocean acidification is another reason for lower rate of fish reproduction activity. Ocean water needs to main a specific ph level. Fish eggs are highly sensitive to the ph level of ocean water. Highly acidic water is also difficult for larvae for finding suitable place habitat. It also disturbs larvae to navigate their way to home.

Due to global warming, sea water level is also rising. And this change is crucial for fish because mangrove forest are good source of food and habitat. And sea level rising is destroying the mangrove forests worldwide. Heavy storm and unusual rainfall is also big problems for the habitat of the fish.

Global warming possess threat in some other indirect way for fishes. Global warming is causing fires in the forest. Intense fires sometimes burn out the root system of the forest. And that may cause erosion and saltation of nearby rivers. That kind of even sometimes alter the ecosystem of the river. Earlier peak river flows in the spring can also be a problem for their navigation. That means if the snow starts to melt before summer that means there will be less waterflow during summer season and that will make difficult for adult fish to return from the ocean. It also makes difficult for the juvenile fish to make it to the ocean. In a word, global warming cause snow melting at the wrong time that makes difficult situation for fishes to navigate from rivers to ocean when they need to move.

Oxygen level of water drops as the atmospheric temperature rises. That creates problem for cold water fishes. Because cold water fishes are extremely sensitive to the water temperature fluctuation. Excess heat in the water makes immune system of fishes very weak. They become more vulnerable to the poisons, parasites and diseases. A river becomes unsuitable as a habitat for fish if the water of the river stay hot for a longer period of time.

Almost 3 billion people depends on fish as their main source of protein. Almost 12 percent of the world population depends on the fishing related jobs worldwide. According to a report of msc.org It creates almost 2.9 trillion dollars of economic benefit every year. However global warming will cause a huge damage to the economic growth of the developing countries if fish populations start to decline.

Source: nwf.org
 msc.org

Image source: Rediff.com