Home Fish Science What do Fish need to Survive? (3-minute Read)

What do Fish need to Survive? (3-minute Read)

by gvald

Fish require certain levels of protein, carbohydrates, fat, vitamins and minerals in their diet to ensure their survival and development. The levels of these different nutrients (or simple foods) vary depending on the diet.


Not all types of fish live in the same types of water. Fish can tolerate different environmental conditions, such as:

  • Different amounts of salt
  • Different amounts of oxygen
  • Different types and amounts of food
  • Different water temperatures
  • Different hiding areas (cover and bottom)
  • Different breeding areas

What do fish need to survive?

Once the environment is adapted, the survival of fishes comes down to few things, a bit like us, they need oxygen and food. There are of course other factors, but this is not dependent on their lives, it is more comfort than anything else.



Without a good supply of oxygen in the water, fish cannot survive. Some fish, like carp, can live with less oxygen than others, like trout. What affects the amount of oxygen in the water?


Perennial plants in a lake or stream infuse oxygen into the water through photosynthesis – the process by which sunlight is used to produce food. Oxygen from the surrounding air can also enter the water. In a stream, water flowing over rocks takes in oxygen from the air.


Decaying plants use the oxygen in the water to decompose. Pollution, in many forms, reduces the amount of oxygen in the water. Chemicals dumped into the water trap oxygen and remove it from the natural system. Thermal pollution – the heating of water by industries – reduces the amount of oxygen the water can hold.


Water temperature affects the amount of oxygen the water can hold. Colder water contains more oxygen molecules than warmer water. Oxygen levels vary from place to place in the same stream.



The amount and type of food available to fish plays an important role in determining their presence in a particular water body. The level of competition with other fish also plays a role.

Each type of fish has its own temperature range where it can survive. Some fish live in a wide range of temperatures, while others require colder water. Although fish may not always be able to find the exact temperature they desire, they are often found in water that is close to that temperature.

The water in which a fish lives must contain enough oxygen. Good quality water supports more fish species and larger fish populations than polluted water. Water that is stagnant, polluted, or lacking in oxygen will support only a limited number of fish.


Good Water Quality

Water quality affects different species in different ways. Some fish can live in poorer water quality than others. For example, carp can live in water that trout could not tolerate.



Cover, such as aquatic plants, rocks, stumps, etc., is essential for many types of fish. Fish choose a particular type of cover for two main reasons. First, it allows them to hide from their enemies. Second, the cover puts it in a very good position to catch an unsuspecting meal or swim by.


In what environment can fish survive?

One of the main factors that differentiate one type of fish from another is salt. Some fish cannot live in a salty environment, and others absolutely need salt to survive. However, some fish species can live in both salt and fresh water!



Freshwater contains much less salt than the ocean. Most ponds, reservoirs and rivers in Canada are freshwater. Fish commonly found in freshwater are common carp, crappie, bass, perch, muskellunge, northern pike, trout and walleye.



Many species of fish live in the salt water of the oceans. It is the kidneys of the fish that allow it to properly balance the salt content in its body. The most common saltwater fish are sablefish, Atlantic cod, yellowtail, sea bass (also found in freshwater), speckled trout, tarpon, tuna, halibut, rockfish, white perch, lingcod and yellowtail snapper.


Brackish waters

An estuary is where freshwater streams and rivers mix with saltwater from the ocean. The amount of salt (the “salinity”) changes every day with the tides, rain, or drought. This water is called “brackish water”. The change in salinity determines the types of fish that can live there.

Some fish live in salt water, but swim against the current in fresh water to lay their eggs. These fish are called “anadromous”. They include salmon and some types of trout.

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