Generally, Gammarus pulex and other amphipods are rather omnivorous than strictly detritivorous freshwater crustaceans (for rivew, see MacNeil et al., 1977).

In particular, G. pulex is most attracted to the aufwuchs on the conditioned discs made of poplar (Populus canadensis) leaves and less to the leaves themselves (De Lange et al., 2005).  According to data obtained by these authors, fungi and bacteria within the conditioned leaves are more important than green algae Scenedesmus obliquus.

Exudates of isopod Asellus aquaticus trigger active feeding behaviour in G. pulex as potential predators (Bengtsson, 1982). It is shown that 15 individuals of A. aquaticus placed in the 1000 ml bottle actively release in the water amino acid exudates. Within the first 2 hours of incubation, arginine (8022 ng per liter), lysine, tryptophan and histidine are most abundant. Wisenden et al. (1999) have also shown that G. minus display feeding responses to odor of squashed sympatric isopod Lirceus fontinalis.

Wudkevich et al. (1997) have exposed Gammarus lacustris to chemical stimuli from injured conspecifics and to chemical stimuli from two types of natural predators: dragonfly larvae, Aeshna eremita, and pike, Esox lucius. An exposure to these three stimuli causes G. lacustris to reduce significantly the level of their activity suggesting the presence of an alarm pheromone in the body tissues of G. lacustris. Similarly, chemical stimuli from sculpin, Cottus gobio, and brown trout, Salmo trutta, induce short decreasing locomotory activity of G. pulex, whereas an odor of freshwater signal crayfish, Pacifastacus leniusculus, is indifferent (Åbjörnsson et al., 2000). There are no significant differences in activity of G. pulex exposed to water scented by sculpin or trout, these responses are also independent of the previous diets (G. pulex or isopod A. aquaticus) of predatory fish.

Yet, Kullman et al. (2008) have examined the tendency to aggregate in G. pulex in the absence and presence of predatory fish odor. In conditioned with the threespined sticklebacks Gasterosteus aculeatus water, amphipods significantly prefer to stay close to conspecifics.

Basic References

Åbjörnsson K., Dahl J., Nyström P., Brönmark C. 2000. Influence of predator and dietary chemical cues on the behaviour and shredding efficiency of Gammarus pulex. Aquatic Ecology 34, 379-387

Bengtsson G. 1982. Energetic costs of amino acid exudation in the interaction between the predator Gammarus pulex L. and the prey Asellus aquaticus L. Journal of Chemical Ecology 8, 1271-1281

De Lange H.J., Lürling M., Van Den Borne B., Peeters E.T.H.M. 2005. Attraction of the amphipod Gammarus pulex to water-borne cues of food. Hydrobiologia 544, 19-25

Kullmann H., Thűnken T., Baldauf S.A., Bakker T.C.M., Frommen J.G. 2008. Fish odour triggers conspecific attraction behaviour in an aquatic invertebrate. Biology Letters 4, 458–460

MacNeil C., Dick J.T., Elwood R.W. 1977. The trophic ecology of freshwater Gammarus spp. (Crustacea: Amphipoda): problems and perspectives concerning the functional feeding group concept. Biological Reviews of the Cambridge Philosophical Society 72, 349-364

Wisenden B.D., Cline A., Sparkes T.C. 1999. Survival benefit to antipredator behavior in the amphipod Gammarus minus in response to injury-released chemical cues from conspecifics and heterospecifics. Ethology 105, 407-414

Wudkevich K., Wisenden B.D., Chivers D.P., Smith R.J.F. 1997. Reactions of Gammarus lacustris (Amphipoda) to chemical stimuli from natural predators and injured conspecifics. Journal of Chemical Ecology 23, 1163-1173