Does compensatory growth modify fish scale shape?

Abstract

Although the shape of fish scales is useful for determining stock membership, the role of extrinsic (e.g. habitat, food type) and intrinsic (e.g. growth) factors in determining variation in fish scales shape has not been determined. This study examined whether fish scale shape changes as a result of compensatory growth in juveniles of the cyprinid roach, Rutilus rutilus (L.) reared on a fish farm in the UK. This was analyzed using geometric morphometric methods. Sufficient evidence was generated to accept the assumption that food availability and type between different growing-out facilities resulted in compensatory growth and this was sufficient to cause scale shape differences. This was tested using multivariate analysis of variance (MANOVA) analysis with the principal components scores of specimens (PCs) as dependent variables, to investigate whether fish scale shape (where the configuration of landmark coordinates were scaled, translated and rotated) form (where the configuration of landmark coordinates were translated and rotated not scaled) and allometry free (allometrically adjusting scale shape according to length) are related to holding facility (as fixed factor). Cross validated discriminant analysis was used to assess and compare the efficacy of shape, form and allometry free information. Identification rates are much better than chance with allometry free and shape alone, and classification is improved when size is taken into account.

Impact of environmental and genetic factors on the scale shape of zebrafish,Danio rerio(Hamilton 1822): A geometric morphometric study

“…compared to the shape of the whole body, scale shape is presumably less sensitive to short-term environmental effects and instantaneous processes, as well as it is less dependent upon the conditional state of fish. In accordance with the observations of Ibáñez et al [12], present results showed that although scale shape might also recover partly during the compensatory growth (i.e. with the normalization of feeding conditions), this process is much slower and presumably is not as complete as it is in condition related body shape parameters.…”

“…Based on positive field experiences, scale shape analysis has recently become a widely used tool for differentiating among populations or stocks of fish species [8,[10][11][12][22][23][24], for all that the background of these differences is still not exactly understood. In this study, it was shown, however, that both genetic and environmental factors contribute to intraspecific variability in scale shape of fish and might induce comparable differences.…”

“…however, the process of taking a proper morphometric image of the whole body is highly stressful for fish, and therefore, the investigation of a structural component, variable enough to distinguish populations and easy to collect without permanently damaging the animal is more expedient [8]. Assuming a strong genetic definiteness, scales, similarly to other hard structural components like otolith [1,17] and in general bony structures [33], are regularly used to distinguish among species or even populations of fish [10][11][12][22][23][24]. The examination of scales proved to be a practical and cheap tool to identify fish including archaeological samples as well [15,30].…”

“…Some studies have already addressed the questions whether the differences observed in the scale shape could be attributed to differences in life histories of populations, and whether environmental factors, such as recovering food quantity (i.e. compensatory growth) [12], or cadmium treatment [26,34] could affect the reliability of scale shape based stock identifications [12]. However, because of the complex effect of numerous factors and the high degree of genetic diversity, it is generally difficult to evaluate the relative importance of specific factors based on field samples [12].…”

“…compensatory growth) [12], or cadmium treatment [26,34] could affect the reliability of scale shape based stock identifications [12]. However, because of the complex effect of numerous factors and the high degree of genetic diversity, it is generally difficult to evaluate the relative importance of specific factors based on field samples [12]. Nevertheless, no controlled laboratory experiment has yet been reported on the potential role of environmental factors in formation of scale shape.…”