Roach habitat shifts and foraging modified by alarm substance 1. Field evidence
Gliwicz, Z. Maciej; Dawidowicz, Piotr
Archiv für Hydrobiologie Volume 150 Number 3 (2001), p. 357 - 376
published: Jan 20, 2001
ArtNo. ESP141015003001, Price: 29.00 €
Under laboratory conditions, roach from the lowland lakes of Europe display a regular and strong fright reaction (aggregating, hiding and reducing feeding rate) in response to cyprinid skin extract used as an alarm substance. However, roach response to the same concentrations of the skin preparation was transitory and obscure in their natural lake habitat (a stratified mesotrophic lake of 87 ha and 27 m maximum depth) where roach was a dominant fish feeding offshore. A short-lasting difference between fish densities in the treatment and reference 20 ha areas, and a small albeit clear difference in their mean depth during evening feeding offshore, were found (echosounding). No difference in gut fullness was found between the roach treatment and reference areas. Vague differences between the treatment and reference areas were also revealed in rudd of another lake (l6 ha area, 26 m maximum depth). The weak response to the alarm substance in the field as compared to the laboratory conditions could result from the fact that fish are less reluctant to accept greater risk under the limiting food levels of natural habitats. Moreover, the reference areas in the field, unlike the reference variants in the laboratory, are not free of alarm substance from the everyday activity of piscivores. The transience of the wild-fish response to alarm substance and their ability to compensate for reduced feeding, show that the undesirable effects of a dominant planktivore on planktonic herbivores cannot be curtailed in a sustainable way by using counterfeit information on increased predation risk in a lake designated for water-quality improvement.