Greater understanding of the habits of invasive carp species is helping researchers tackle the threat they pose to many aquatic environments, particularly in the US.

First introduced to US waters in the 1970s in a bid to control the growth of weeds and algae in ponds, fish such as bighead, silver, black and grass carp – collectively referred to as invasive carp – escaped into waterways after severe flooding and have been spreading upstream.

As we learn more about their behaviour in these waterways, it is clear decisive action is needed to prevent irreversible damage to ecosystems.

Conditions for egg development

Invasive carp tend to prefer slow moving water, but will spawn in areas with a faster current because eggs develop as they float downstream and may not survive if they sink to the bottom. 

Temperatures of 18 to 30 degrees C are ideal for spawning, as this range stimulates early development of the eggs. A long river is also necessary for development because it provides time for eggs to be suspended in the water column, while flood plains encourage development in juveniles.

Age of maturity varies between species, as do eating habits, with the Minnesota Aquatic Invasive Species Research Center (MAISRC) noting the following characteristics:

  • Bighead carp – Mature between 2 and 7 years old, with each female producing up to one million eggs per year. Adults and juveniles consume zooplankton.
  • Silver carp – Mature between 2 and 6 years old, with a single female producing as many as two million eggs each year. Adults eat phytoplankton, while juveniles also consume zooplankton.
  • Grass carp – Mature between 4 and 7 years, with each female producing up to two million eggs each year. Adults eat aquatic and terrestrial plants, while juveniles tend to prey on aquatic invertebrates.

Overwhelming ecosystems

The sheer volume of eggs produced by invasive carp species allows them to quickly overwhelm ecosystems and threaten the survival of native species.

Many will consume as much as 20% of their body weight each day, leaving little to support other fish, while scientists have raised concerns these species carry parasites that could do additional harm.

Bighead carp can live for at least 9 years, while silver carp live as long as 20 years. This lifespan, combined with the potential for rapid proliferation, gives these species the ability to dominate an ecosystem within a short space of time.

Researchers at organisations such as MAISRC are now studying ways to prevent upstream migration, combining laboratory trials with field tests. An exceptionally good sense of hearing makes acoustic deterrents ideal, while more drastic measures such as the use of pathogens are also under consideration.

Further Reading