Ligula intestinalis


Ligula is thought to be the most important tapeworm that infests cyprinids and can be a major threat to natural and farmed fish populations. The adult worms can be from 10-100cm in length and up too 1.2cm in width. The virulent nature of this parasite leads it to commonly filling every available space within the body cavity whatever the initial size of the host; the weight of the parasite can, on many occasions, exceed the total body weight of the fish. Once hosted by the fish the parasite will usually reside in the body cavity for the duration of the fish's life.

The importance of this parasite is justified when considering the fish species it hosts. In the UK it can be found in the body cavities of roach, rudd, gudgeon, bream and dace.


 

Interestingly, the fish is not the major host of Ligula; the cycle starts in the body of birds. The life expectancy in the major host is a maximum of 5 days, but in this time they will lay a multitude of eggs. These eggs are passed into water via the faeces of the bird. Once in the aquatic medium they hatch and are eaten by a wide range of copepod zooplankton. The cycle continues when the fish ingests the copepod. The worm then burrows through the gut wall and continues to develop in the fish's body cavity. The cycle is then complete when the bird eats the tapeworm hosting fish.

There are numerous health implications when hosting Ligula. Clear distension of the body wall as the worm increases in size is probably the most visually astounding feature. This distension can cause impairment of muscle development and also reduces streamlining; this causes and increased risk of predation. There can also be affects on several blood parameters. Reduced growth, anemia, dark colouration and erratic swimming are also side affects of ligula, but the largest chance of mortality occurs through the susceptibility of secondary infections.

Atractolytocestus huronensis (hosts - carp) Bothriocephalus acheilognathi (host - carp)
Monobothrium wageneri (host - tench) Ligula intestinalis (host - cyprinid sp.)
 
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