What is fish habitat?

Certain characteristics of the aquatic environment are essential to the survival of fish. Fish must be able to access the following features or habitat components at various stages of their life cycle to survive and thrive:

• a place to reproduce (spawn), and nursery and rearing areas
• access to food
• adequate shelter and cover
• access to other habitats (connectivity)

What makes an ‘ideal habitat’ depends on the species type and its life-cycle stage. Water quality parameters (temperature, salinity, pH, and dissolved oxygen), physical features (water depth and flow rates, substrate material, types of vegetation, and connections to other habitats), and other organisms in the environment are all important characteristics that will dictate which species you will find in a habitat.

Suitable spawning habitat

Most fish species have specific requirements for where they will deposit their eggs, and they will invest a great deal of energy to find the right place. Some species prefer spawning areas with abundant aquatic vegetation, while others require gravelly shoals shaped by wave action and still others prefer areas with an upwelling of groundwater.

Suitable spawning areas are often unique or limited to a water body and differ from areas that fish use to feed or grow from juveniles into adults.

The times that fish species choose to reproduce can also vary. Cold-water fish generally spawn in the spring or fall while cool and warm-water species prefer spring and early summer.

If spawning habitats are degraded, then the fish who usually reproduce there will abandon them. For lack of appropriate places to spawn, certain fish populations may decrease in abundance, and as a result, compromise a water body’s ecological balance.

Access to food

Young fish need to eat soon after they have hatched. Most start by eating plankton before moving on to larger prey, such as insects and even other fish.

The quality of the riparian zone determines what food is available because its aquatic vegetation serves as a refuge for insects and fish at the bottom of the aquatic food chain, and shoreline trees and shrubs provide a source of food for these ‘fish food’ species.

So, although it may not be obvious right away, cutting down shoreline vegetation can undermine the survival of fish.

Adequate shelter and cover

Fish are sometimes predators and sometimes prey. As prey, fish have a better chance of survival if they can access a place to escape their predators, such as around logs, rocks, and aquatic vegetation in shallow water.

The types of cover fish use can vary over their lifetime. For example, a young pike stays near shorelines in shallow waters with vegetation and fallen branches to evade its predators, but as it matures, the fish will move to deeper water offshore and use submerged logs as cover to ambush its prey.

If we clean up swimming areas or access to a water body by removing logs, rocks, and vegetation, we are taking precious cover away from fish. They will then have to leave these areas to go to other places that may not fully meet their requirements.

Access to other habitats

While structures such as dams and watercourse crossings provide numerous benefits, such as hydro-power generation, and are required for connected road and rail networks, they can form barriers that disrupt ecological processes – disconnecting rivers and lakes from wetlands and floodplains, altering water flows and impacting the movement of sediment. This ‘disconnection’ is sometimes called aquatic habitat fragmentation or loss of aquatic connectivity.

Barriers also limit the movement of aquatic species within a watershed. All fish need to migrate between different habitats to survive – they need specific places to feed, take cover, rest, and reproduce. An example of a fish species that must be able to migrate to complete its lifecycle is Atlantic salmon, who live in marine environments as adults and migrate into freshwater areas to spawn.

Obstacles as small as a 30 cm high weir or an embankment of a few dozen square meters may constitute impassable barriers for fish and prevent them from reaching sites that are essential to their survival. Individual fish health can also be impacted when barriers cause fish to expend more energy than normal to move through barrier structures.