Gammarus fasciatus

Gammarus fasciatus is found anywhere in the freshwater lakes and freshwater rivers. The species is considered the shrimp of Hamilton Harbour. (McMaster University 5/10/01)

Gammarus fasciatus lives in freshwater lakes and rivers, where salinity is very low (1% or less of the salinity present in sea water). It can also be detected in upper parts of estuaries. The species is characteristically found in warm, slow moving waters. Their habitat is characterized by highly oxygenated water and vegetation. In addition, the species lives in shallow waters. A study performed by Lonrad and Kolasa showed that only 4.1% of the population observed were found at a depth of 3m. The majority were found at a depth of 1m.

(Waterman 1960; Vernberg 1983; McMaster University 5/10/01)

Similarly to other members of the family Gammaridae, Gammarus fasciatus is laterally flattened from side to side. They have no carapace or stalked eyes. The anterior end of the species is characterized by the head (which is composed of six compound segments), and 2 antennae. The main body consists of the thorax (composed of 7 segments called pereonites), the abdomen (composed of 3 segments, the pleonites) followed by the uronites. The thorax is accompanied by 7 thoracic limbs called pereopods. The front two are used primarily for capturing food and the others function as walking legs. The abdomen is accompanied by three more legs, the pleopods. A special characteristic is the uropods, which are three small legs in the posterior end of the scud.

As many invertebrates, Gammarus fasciatus has an open circulatory system. The digestive system is categorized by a foregut, midgut and hindgut. Respiration is based on the function of the gills. The species uses the legs to create currents and bring along oxygenated water. Excretion is facilitated by the function of the antennal gland. As opposed to marine crustacea and some other freshwater species who produce isotonic urine, Gammarus fasciatus can produce urine hypotonic to the blood.

(Anonymous 1, 4/27/01; Anonymous 2, 4/27/01; Lockwood 1967; McMaster University, 5/10/01)

As in many malacostraca the mating process is preceded by preliminary behaviors such as special movements, like dances performed by the male in order to attract the female. The legs play an important role in reproduction. The sexually mature male clasps the female with the second pair of his legs and carries her with him as he is swimming or walking. The male pleopods do not function in copulation. The ova develop in the brood pouch, which are projections of the female legs. Hatching occurs after all the appendages of the embryo have developed. The young usually remain in the mother's marsupium until it is delivered by the female. Unlike other Crustacea, the young Gammarus fasciatus do not undergo metamorphosis.

(Larousse Encyclopedia of the Animal World 1975; Meglitsch 1991; Pearse 1987; McMaster University)

Gammarus fasciatus uses its legs (pereopods and pleopods) to walk on the solid surfaces of the freshwater environment. Locomotion is also described by swimming in the fresh, slow moving waters of its environment. G. fasciatus uses its first pair of legs to also create current and capture food. Courtship behavior is described above in the Reproduction section.

(Waterman 1960)

The mouthparts of the freshwater scud are located in the anterior end of the animal. The antennae, mandibles, maxillules, and maxillae are the body parts used for capturing and eating food. The thoracic limbs secondarily function in the grasping of the food by filtering, creating water current to attract food, and catching food.

Gammarus fasciatus is generally categorized as an omnivore. Their diet consists of algae, detritus, and fungi. The consumption of captured animal food or animal matter eaten and left by scavengers enriches their diet. Vegetable matter and phytoplankton are the primary producers that provide their nutrients to primary consumers such as Gammarus fasciatus. To complete the food web, the primary consumers can be eaten by the secondary consumers such as crabs and weakfish.

The diet of the young is usually based on small algae and animal food and it increases as the species grows.

(Waterman 1960; McMaster University 5/10/01)

Gammarus fasciatus has been considered a biomonitor. This means that they provide methods that can measure levels of particular metals in their environment. A model tested in 1994 by Amyot et al. showed that the uptake of nickel, lead, and cadmium by the species could predict the presence of these metals in their habitat.

(Gammarus fasciatus:Potential Biomonitors 5/10/01)

No negative effect of the species on humans has so far been observed.

Gammarus fasciatus is one of the most sensitive freshwater organisms to toxic substances such as diazinon and chlorpyrifos.

(Lee 1999)