Characteristics of different populations of the gudgeon (Gobio gobio L.) in Flanders, Belgium

We examined the possible effects of isolation on population characteristics of the gudgeon, Gobio gobio L., 1758. Isolated populations appeared to have significantly lower densities than non-isolated populations. Length-frequency distributions showed that most non-isolated populations had a healthy composition, with a larger number of young animals, and a smaller number of older animals. However, for some isolated populations this was not the case, despite the fact that some of them had high densities. Four condition factors were compared between isolated and non-isolated populations. They showed no relationship with isolation, although significant differences among populations were found. Fluctuating asymmetry (FA) was determined using metric and meristic traits. The meristic traits could not detect the presence of FA, but the metric traits showed that FA was present in some populations. Significant differences were found among populations, but the FA could not be related to isolation. The growth rate showed significant differences among populations, but was not related with isolation. The maximum swimming speed, oxygen consumption, ammonia production, and ammonium quotient were assessed in the laboratory. None of these parameters showed a relationship with isolation, but there were significant differences among populations. Overall, our results show that population density and distribution seem to be affected by isolation, while for the other parameters no effects of isolation were found. However, significant differences among populations were found for all other parameters.