Aggressive behaviour between Gymnocharacinus bergi (Pisces, Characidae) and other Neotropical fishes from a thermal stream in Patagonia

SILVIA ORTUBAY; MARIANA LOZADA; V´ıCTOR CUSSAC

ENVIRONMENTAL BIOLOGY OF FISHES

Año: 2002 vol. 63 p. 341 - 366

0378-1909

Gymnocharacinus bergi is a stenothermal endangered fish only found in the headwaters of a thermal stream withinthe temperate Somuncur´a Plateau (Patagonia, Argentina). In spite of the presence of other fish species in theValcheta Stream basin, none of these has been found at the headwaters. Temperature and salinity cannot accountfor the absence of extremely eurytopic Cnesterodon and Jenynsia. In addition, there is no evidence of diet overlappingor territory defence between these species and G. bergi. Therefore, we hypothesise that agonistic behaviourmight be related to G. bergi’s isolation. Experiments were performed in order to analyse interspecific interactionbetween G. bergi and individuals of the other two species. Cnesterodon decemmaculatus showed a submissivebehaviour while Jenynsia multidentata was clearly aggressive. G. bergi decreased its aggressive behaviour towardsC. decemmaculatus throughout the experiment. However, when placed with J. multidentata, its aggressive behaviourdid not diminish.We suggest that the characteristics of the agonistic behaviour displayed by J. multidentata, oppositefrom those displayed by C. decemmaculatus, might account for the absence of J. multidentata in G. bergi’s presenthabitat. With respect to C. decemmaculatus, other factors such as its low counter current swimming ability mightplay a major role in this phenomenon.