Fish Migration

By WONNE Afronelly

Fish form an important link in the food web, from food for wildlife to food for humans, as well as providing nutrients for plants when they die. Small, medium and large fish are an essential part of human natural heritage.

According to the World Fish Migration Foundation, about 50 million people in the Mekong River basin depend on the river and the food it provides for nutrition and income. The collapse of fish stocks has a devastating effect on the food security of these people, which includes millions of the world’s poorest people.

What is Fish Migration?
Fish Migration is a situation triggered by natural or human-made factors that make fishes swim short or long distances daily, yearly, or longer, either to complete life cycle or to avert danger and pollution. Fish migration is necessary for the success and prosperity of aquatic life.

Is Fish Migration the same as Migratory Fish?
Nope. Migratory fish are species that require different environments for significant phases of their life cycle, such as reproduction, production of babies, growth and sexual maturation, and lovemaking. Are you surprised at lovemaking? Well… the butterflyfish are known to stay loyal to one partner in their lifetime.

Three Types of Migratory Fish

Potamodromous species like Carps are freshwater fish and live their entire life cycle within inland waters of a river system, but migrate across distances for different purposes within the river.
Oceanodromous species like Tunas live their entire life cycle in the sea but migrate long distances for different purposes as well.
Diadromous migrate between fresh and saltwater and has two types anadromous and catadromous.

Anadromous species like the salmon hatch in freshwater, but their growth phase in the sea. They migrate back to freshwater for spawning and breeding.

Catadromous species like the eel, are the opposite! They are usually found in freshwater habitats but migrate to sea to spawn and for breeding.

Why do fish migrate? 

  • Search for food and water.
  • Reproduction, production of juveniles, growth, and sexual maturation.
  • Proper osmoregulation and more suitable climate conditions.
  • Human environmental pollutants: artificial light, noise, water abstraction, barrier installation, habitat destruction, or incidence of chemical pollution.

Benefits and Importance of Fish Migration

Primary Food Source 
Many human populations depend on the presence of predictable migrations of fish for their subsistence and livelihoods.

Conservation and Procreation
Fish migration is significant for the proper environmental conditions for spawning to prevent the extinction of species. 

Sustainable exploitation
Fish migration enables fast-moving species to settle in areas incapable of inhabitation by otherwise slow rapid fish swimmers as well as exploit fluctuating resources.

Implications and Barriers to Fish Migration

Loss of Livelihoods
When fish can’t complete their migration because of barriers to fish passage – like dams, road culverts, low water levels, and sluices, it recklessly distorts the food web. More than 6 million barriers in the U.S. alone keep fish and other aquatic species like mussels, from reaching their travel destinations. 

Loss of Habitat and reproduction sites 
Construction of dams, sluices, affects migratory fish habitat. Transformation of lotic to lentic environment habitats can cause the elimination of species that spawn in relatively fast-flowing water during or after river impoundment.

Solutions: Why help fish migrate?

To help stabilize food security and livelihoods as well as sustainable economic growth of valued commercial fish species. Sustainable migration techniques would ensure fish can pass to accommodate species of different migratory behavior, size, and swimming ability especially small catadromous species with limited swimming abilities, which can help reduce the implications of barriers to fish migration. 

Every effort will help recover threatened and endangered migratory fish and support sustainability, so we need to play a positive role today no matter how little.