Ontogenetic variability in external morphology of native (Canadian) and non-native (Slovak) populations of pumpkinseed Lepomis gibbosus (Linnaeus 1758)

External morphology of native Canadian (River Otonabee, Looncall Lake) and non-native Slovak (River Danube) pumpkinseed was examined using both triple regression analysis (distance-based measurements) and geometrical analysis (coordinate-based measurements) within an ontogenetical aspect. In general, the results from the geometrical analysis comply with those from the triple regression analysis. The smallest pumpkinseed (predominantly juveniles) differed significantly from the largest pumpkinseed (predominantly adults) in all the three populations. The major difference was that adults had a deeper body and larger belly area than juveniles, which is probably associated with more space for gonads in mature fish. Developmental patterns and external morphology in pumpkinseed from the River Otonabee seemed to be closer to pumpkinseed from the Danube than to those from Lake Looncall. This suggests that, in the pumpkinseed examined, ontogenetic changes in external shape depend on environmental conditions (epigenetical information) rather than on geographical and/or genetical isolation. Further examination of early development, fecundity, number of spawning acts per season, parental care, egg size, age at maturation, etc., will follow to test this hypothesis.