Carp were first recorded in Victoria in 1862. However, it was not until the 1960's that the Boolara strain spread and infested the Murray Darling Basin.

Queensland

There is a genetic difference between Murray-Darling carp and Logan-Albert carp. This suggests separate introductions of carp to these two river systems. It is likely that those in the Murray-Darling spread from carp populations in New South Wales and Victoria into Queensland.

Distribution in Queensland

Carp are present in the following sections of the Murray-Darling in Queensland: Condamine-Balonne catchment, Paroo River, Warrego River, Nebine Creek, Culgoa River, Barwon River and MacIntyre River. Carp in these rivers comprise approximately 20 to 30 per cent of the total fish population.

Carp are also very abundant in the Logan and Albert rivers in south-east Queensland.

Potential for spread

Carp have considerable potential to spread throughout Australia as a result of their wide environmental tolerances.

Biology

There are several varieties (or strains) of Cyprinus carpio. These include carp (often referred to as common or European carp), Koi carp and mirror carp. They have very similar impacts on the environment.
Carp can be identified by the two barbels (whiskers) on either corner of their upper lip. Other distinguishing features include a forked tail, single dorsal fin and large scales. They are usually bronze or olive-green with a pale yellow to ivory underbelly.
Wild-form goldfish are often confused with carp as they revert to an olive-bronze colour in the wild. Goldfish do not have barbels.
Carp occasionally crossbreed with goldfish (Carassius auratus). Further research is required to establish whether goldfish-carp hybrids are fertile.

Reproduction

Female carp mature between 3 and 4 years of age and males between 1 and 3 years. They can live for up to 17 years.
Carp spawn several times in a season (from September to December in Australia), producing 80 000 to 1.5 million eggs. However, very few of the eggs survive to become mature fish.

Environmental tolerances

Carp have broad environmental tolerances. They can tolerate a wide range of temperatures (4-35°C) and moderately acidic water and are particularly tolerant of poor water quality - low oxygen concentration, high turbidity (muddiness), moderate salinity and high toxicant loads -which enables them to survive in conditions unsuitable for native fish.

Habitat preferences

Carp typically inhabit mid-latitude, low-altitude, slow-flowing rivers or standing waters. They are rarely found in clear, cool and swift-flowing streams.

Movement

Carp is a very mobile species, migrating up and down rivers throughout the year. This migration may be related to water temperature, food availability and nesting sites. Recent studies indicate that carp prefer to live in one area but individual fish are capable of moving long distances.

Feeding habits

Carp feed by filtering food from the water or sieving it from bottom sediments. They take sediment into their mouths and then expel the inorganic particles. This is called 'roiling'. In Australia, larval stages of carp feed on zooplankton (microscopic animals) and adults feed on crustaceans such as shrimp, aquatic insects and some plant material. Carp are opportunistic omnivores (i.e. eat whatever animal and plant matter is available). The diet of goldfish-carp hybrids is similar to that of carp.

Effect on environment

It is thought that carp may have a number of negative effects on the aquatic environment. However, a range of other factors could also be causing them.

More research is needed to determine the extent of damage actually caused by the carp.

Possible effects include:

Reduced water quality.

Carp feeding behaviour continually stirs up the bottom sediments, resulting in increased turbidity. This reduces the amount of light entering the water, which makes it difficult for plants to grow and produce oxygen and has detrimental effects on fish that rely on vision to locate their food.
Decline in native fish numbers.

There is anecdotal (non-scientific) evidence that carp displace native fishes. However, there is little scientific evidence to support this, despite the fact that carp are often the most common fish in a waterway. It is thought that increased carp populations may be a result of declining native fish populations rather than the cause.
Reduction in aquatic plants.

Studies indicate that carp can have quite a significant effect on aquatic plants through direct grazing (eating), physical uprooting of plants when feeding and increased turbidity. Shallow-rooted, soft-leaved and submerged vegetation is the most likely to be affected by carp.
Decline in small native animals such as insects and grubs.
Erosion.

Carp have been blamed for increased erosion of banks. However, this is difficult to prove as many other factors also cause erosion, such as felling trees on river banks and poor farming techniques.
Algal blooms.

Studies outside Australia have indicated that carp waste products increase nutrient levels, resulting in an increased concentration of phytoplankton (microscopic plants). However, carp density would have to be very high for this to have a significant effect. Whether carp are responsible for algal blooms in Australia is yet to be proven.
Degrading recreational areas.

High numbers of carp make areas less popular with recreational fishers. The high numbers plus the likely impacts, such as increased turbidity and a reduction in the number of aquatic plants, can also make an area less popular with tourists.

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Student resource i.2 Introductory

Priority species: Carp (Cyprinus carpio)

History of introduction

Australia