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Stickleback - (Gasterosteus aculeatus).

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Introduction

Stickleback. (Gasterosteus aculeatus) Sticklebacks are small, bony fish that exist throughout most of the world and are known to have a wide variety of subspecies, (for example Gasterosteus aculeatus williamsoni) that have phenotypically adapted to various environmental factors. They are small fish (2-4 inches) and are characterized by a row of free dorsal fins in front of the dorsal fin combined with the absence of scales. Male sticklebacks build intricate golf ball-sized nests, which he guards aggressively. Both males and females come together for a mating rituals. Breeding typically starts between the second and third year in the spring and summer. Males start to develop a deep red coloration on their throats and a blue tint in the eyes. They establish their territories by chasing other rival males away from their nesting site. Receptive females are led back to the nest where she deposits her eggs. The eggs are immediately fertilized by the male who then chases the female away. ...read more.

Middle

The egg of this cestode has a thin walled operculum, which upon hatching, releases the larvae. The free-swimming ciliated larvae development depends on factors such as temperature where cooler temperatures result in longer duration. The larvae is ingested by a Cyclops and the ciliated epidermis is shed inside to release the newly developed procercoid. The contagion of the stickleback occurs upon ingestion of the copepod. The procercoid develops into a plerocercoid and it starts to develop segmented proglottids once inside the gut of the stickleback. Infection of the stickleback by Schistocephalus solidus can be quite high, 14 worms and can be up to 92% of the body weight or even exceed it. Schistocephalus solidus induces a number of changes in its intermediate host, the threespine stickleback. This includes phenotypic changes that may improve the host fitness for predation. Behavioral changes may also enhance the infected stickleback to become a target for a definitive bird host. Because of these changes, the chance of the parasite to reach its next life cycle increases substantially. ...read more.

Conclusion

At the anterior end it has a sucker which has two central large hooks surrounded by 16 smaller hooks for attachment to the host. Trichodina species is a protozoa. The genus contains as many as 200 species, most of which are parasites on aquatic invertebrares, fish and amphibian. They are characterised by the presence of rows of cilia and sclerotised "teeth" that are used to attach the organism to the host. This protozoa swims freely in the water so transmit to the host at no specific time. Tricodina occurred only in 1998 and in particularily high prevelance in 1999. It cause extensive tissue damage to the host as it feeds and can lead to suffocation of the fish. Echinorhynchus clavula and Neoechinorhynchus rutili are both acanthocephala. They have proboscis at the anterior end of the worm with hooks, Echinorhynchus clavula having up to 200 hooks, Neoechinorhynchus rutili having 18 hooks. The most noticeable difference between the sexes of acanthocephala is that of body size, the female specimen is longer than the male and differences in size and shape of the proboscis, hooks, distribution of body spines, and the presence of papillae. ...read more.

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