Classification by salt concentration in water
The most commonly used classification
Primary freshwater fish, fish that can only live in fresh water all their lives. It accounts for 33. 1% of the total fish in the world, with about 8600 species.
Secondary freshwater fish, which lives in fresh water for most of its life, occasionally moves or inhabits brackish water and seawater. It accounts for 8. 1% of the total fish in the world, about 2 100 species.
Peripheral freshwater fish, which inhabit seawater or brackish water, will also live in fresh water or migrate into brackish water. Including upstream fish, downstream fish and marine fish that occasionally enter rivers. It accounts for 0.6% of the total fish in the world, about 160 species.
Classification by evolution, habitat and habits
Pure freshwater fish, fish that live in fresh water all their lives.
Migratory fish (two-way migratory fish) live in fresh water, ocean and other waters with different salinity at a certain period in their professional history. Include anadromous fish and downgoing fish. Sealed migratory fish on land geographically isolated from the sea.
Estuary fish, all fish that live at the intersection of fresh water, salt water and seawater.
It can be seen that both migratory and estuarine fish can live in seawater.
The order of salt tolerance of several freshwater fishes in the Yangtze River is bighead carp > grass carp > Megalobrama amblycephala > silver carp and its safe concentration is 1.5 1, and the upper limit of embryo salinity is 1.4. So these fish will die in the sea, so when raising these fish, we should control the PH value of these fish ponds.
This question is very pertinent, and the landlord didn't ask it wrong. And logical thinking is accurate.
I am in Weihai, Shandong. We are surrounded by the sea on three sides, with many estuaries and many fresh water reservoirs. We call the tributaries of the estuary' two living waters', and there are two special species of living fish in the two living waters, namely, shrimp and crab, freshwater fish and marine fish.
For example, two specialized aquatic species, puffer fish, jumping fish, barracuda and so on. , all like to be active in two living water areas or estuaries. Many people didn't expect that there were puffer fish in the estuary area.
In the estuary area and the area near the estuary, the proportion of fresh water is different, and the range of activities of marine fish and freshwater fish is also different. The most neutral areas are live fish (floating flowers), crucian carp and hairy crabs (similar to hairy crabs but thin). In addition to barracuda, puffer fish and jumping fish, there are some small fish species such as small black fish beans and third orders.
It is difficult to see big fish in the area where there are two flowing waters in the estuary, that is to say, even if freshwater fish species go downstream and marine fish go upstream, they have their own adaptability and comfort, and adjust their swimming range with the salinity of water. Just as we go to the plateau in the plain area, the body can obviously feel the change and adaptability.
Then the fish in the upstream go up to the general range of activities, and the fish in the flowing water still like to swim upstream, and the fish swimming downstream will be easily injured.
We also use fresh water loach to catch sea bass (dipped in seven-star perch flowers). Under normal circumstances, loach can survive for a long time in water storage and has strong vitality. Generally, it won't work in pure seawater for at most an hour.