Tuesday, February 7, 2012

Euhaplorchis californiensis: Controlling minds of fishes'

Title: Euhaplorchis californiensis: Controlling minds of fishes’

A cyst on the fish's brain http://happycleananimals.wikispaces.com/Euhaplorchis+Californiensis 


Euhaplorchis californiensis is a common common trematode in southern California and Baja California estuaries that spends most part of its life parasitizing in the brain of the Pacific killifish (Fundulus parvipinnis), one of the most common fishes in these estuaries and second intermediate host. E. californiensis has three hosts in its life cycle, i.e.,horn snails (Cerithidea californica), California killifish (Fundulus parvipinnis), and shorebirds [1]. The cercariae swim from their first intermediate host snail, penetrate into the skin of killifish then migrating into their brain as metacercariae. Once inside the brain, metacercariae encyst in the meningeal layer and on the brain surface [1]. The infected killifish display 4 times as many conspicuous swimming behaviors as uninfected ones, rendering them 10–30 times more likely to be eaten by birds, the parasite’s final host [1]. E.californiensis is found near the Pacific coast of California and northern Mexico [1].  

Symbiont description:

Euhaplorchis californiensis, a trophically transmitted parasite is a parasitic fluke from the phylum Platyhelminthes and the class Trematoda [1]. As with many trophically transmitted parasites, E. californiensis modifies behavior of the host to increase the likelihood of transmission to the next host (predator) [2]. The worm’s definitive hosts are a variety of shorebirds [2]. The fluke must get into the birds’ digestive system in order to reproduce.  This parasite matures in shorebirds, which feed on infected killifish than on uninfected fish [2]. 

Host description:

The definitive host where the parasite matures is the shorebirds [2]. The parasite, E.californiensis, has intermediate hosts, first being horn snails (Cerithidea californica) and the second one being Pacific killifish (Fundulus parvipinnis) [3]. The parasite is heteroxeneous because there is more than one host involved.

Life Cycle:

The lifecycle of E.californiensis is simple to understand. First, the eggs of E. californiensis are passed out through bird droppings. They are consumed by horn snails. The larvae of the worm develops inside the snail, while living inside a snail after hatching, E. californiensis inhibits the snail’s fertility for several generations. The cercariae swim out into the marsh waiting to be eaten by the killifish [4]. Second, in the killifish the cercariae cysts the fish’s brain causing it to swim near the surface and shimmer making it obvious to be eaten by a bird [4]. Third, the shorebirds eat the killifish along with the worm. The worm lays its eggs in the digestive system of the bird. The eggs are excreted around marshes and ponds where snails can feed on and continue the life cycle again [4].


Initially, there aren't any consequences since the predator in this host-parasite interaction benefits by acquiring food easily. According to Claude Combes, "Based on outdoor experiments, Lafferty and Morris estimated that after twenty days about 80% of the fish that were infected by more than 1400 metacercariae were eaten, versus approximately 20% of those infected by fewer than only 2% of those that were ininfected. [5]" According to Lafferty's observation on the performance of a population of unparasitized snails in the absence of infected snails, he found that they released more eggs and became densely populated [1]. Also if there weren't any parasitized snails in the natural environment the snail population will nearly double the amount [1]. 

An example of making the host more visible to the predator:

According to Claude Combes, “the last means used to get an infected host eaten, which may be the most common strategy of all, consists of making the host more conspicuous [5].” In other words, healthy parasitized species behave differently due to changes in behavior that may not have any effect on transmission but may cause the parasitized upstream host to be eaten by the downstream host [5]. Euhaplorchis californiensis infects the Pacific killifish (Fundulus parvipennis) that induces abnormal behavior in the fish such as flashing, shimmering, jerking etc and such abnormal behaviors increase predation by birds [5].


[1] Shaw, J.C. "Ecology of the Brain Trematode Euhaplorchis californiensis and its host, The California killifish (Fundulus Parvipinnis)." Journal of Parasitologists 2010. 96.3 (2010): 482-90.

[2] Fleisher, Paul. Parasites Launching onto a free lunch. Minneapolis, Minnesota: 2006. 85-6.

[3] Lafferty, Kevin D. "Altered Behvaior of Parasitized Killifish Increases Susceptibility to Predation by Bird Final Hosts." Ecological Society of America. 77.5 (1996): 1390-97.

[5] Combes, Claude. Parasitism: The Ecology and Evolution of Intimate Interactions. Chicago: 2001. 257.

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