Yesterday, near the Donggu tide gate on the Haihe River, several kilometers away from the site of the major explosion in Tianjin Port, a large number of dead fish were found floating next to a 200-meter embankment. The widest part was about four to five meters, and dozens of people were gathered to observe. What could be the cause of this massive fish death?
Poisoning leading to fish death
Fish have a single living environment and relatively poor resistance to toxins compared to other animals. Once toxins enter their living environment and the concentration exceeds the maximum dose that fish can tolerate, it will lead to a large number of fish deaths. This type of death is also related to the size and species of the fish. However, fish deaths caused by water poisoning often involve multiple species of fish dying simultaneously, and the relationship between the death of a single species of fish and poisoning is not significant.
Eutrophication leading to fish death
Eutrophication refers to an excessive amount of nutrients in the water, especially inorganic salts containing nitrogen and phosphorus. A large amount of domestic sewage (containing nitrogen and phosphorus) and industrial wastewater containing a large amount of organic matter are directly discharged into rivers, causing rapid increases in nutrients such as phosphorus, nitrogen, trace elements like iron and manganese, and some organic compounds in the water. This is when "eutrophication" occurs.
Excessive nutrients cause excessive growth of algae in seawater. Algae produce some highly toxic toxins, some of which are as toxic as pufferfish toxins. When marine animals consume these algae, the toxins accumulate in their bodies. At the same time, a large amount of algae need to respire and consume oxygen, leading to oxygen depletion in the water and causing massive deaths of fish, shrimp, and shellfish.
Seasonal reasons
Many fish species inexplicably die in large numbers in the summer. The main reason is that these fish are highly sensitive to temperature. In the summer and autumn, when the temperature rises, these fish cannot withstand the high temperatures caused by seasonal changes, resulting in large-scale deaths.
Weather reasons
Long periods of thunderstorms and rainy weather with low atmospheric pressure lead to low oxygen concentration in the water. Especially for fish populations that live in groups, they have a high demand for oxygen in the water. Due to weather conditions, they are prone to oxygen deficiency, which may also result in large-scale fish deaths.
Changes in water quality
Water can be classified as fresh water or salt water. Many freshwater fish cannot adapt to salt water. As freshwater fish flow downstream with rivers, at the junction of fresh and salt water, many fish die in large numbers due to their inability to adapt.
