Intestine Morphometrics of Fishes: A Compilation and Analysis of Bibliographic Data

Abstract

Background. The examination of morphological features r elated to feeding in fish, as well as their relation with body length, are of increasing scientific interest. In the present study, information on intestine (gut) morphomet- rics that appear in the relevant literature has been compiled, analysed, and discussed. Materials and Methods. Search of gut-related bibliography was conducted, using online literature databases on fish feeding and ecomorphology. The resulted data was tabulated. Relationships between mean, m inimum, and maximum relative gut length (RGL) and intestine length weight index (ILW, Zihler's index), as provided by the original author, with species' fractional trophic levels (TROPHs; extracted from FishBase) were explored. Finally, using the relations between gut length (GL) and body length (L) provided by the original authors, regres- sions were reconstructed and compared based on species' feeding habits and taxonomy. Results. The amount of information related t o gut morphometrics referred to 498 species. The relations between GL and L referred to 71 species, but four species were omitted from the analyses. Mean, minimum, and maxi- mum RLG and ILW values were negatively related (for all cases: P < 0.01) with TROPH. The GL-L regressions performed for 67 species revealed the presence of two major groups as herbivorous fishes and carnivorous fish- es. Grouping according to species' taxonomic order did not form any significant g roupings. Conclusion. Existing information on intestine morphometrics is generally accumulated in a few scientific papers. All the analyses performed on the compiled data reinforced the pattern generally accepted that herbivores have longer intestines than carnivores. In addition, the influence of species' evolutionary history on comparisons of gut length between species with different feeding habits was not verified. Finally, equations relating RGL and ILW t o TROPH can be used for TROPH value estimates from morphological data that are easy to obtain, espe- cially in the lack of species' feeding habits data.