Trait-based approaches are increasingly popular in ecology to describe communities andtheir responses to natural or anthropogenic changes. Morphology is an integrative trait that combinesfunctional and evolutionary information. However, the objective and quantitative description of themorphological diversity is quite challenging. Modern morphometrics encompass an array of mathe-matical approaches that turn shapes into quantitative variables. For models with no or only a fewhomologous points, outline analysis (e.g., elliptical Fourier transform) converts the outline geometryinto quantitative variables, which can be used in the multivariate framework. The elliptical Fouriertransform here describes the shape of 85fish species found in the North Sea. This study shows thatthe main component of morphological diversity in the North sea is the elongation and developmentof dorsal, pelvic, and caudalfins. The spatial distribution of morphological diversity decreases along alatitudinal gradient, with higher diversity in the southern part of the study area. Compared to speciesdiversity, our results indicate that environmental conditionsfilter morphological traits in the northernNorth Sea. Outline analysis is a powerful approach to provide an objective description offish mor-phology and to improve our understanding of the diversity of large marine ecosystems.