Abstract: IntroductionFish morphometrics has been in the hot-spot of ichthyological studies for many decades, but the initial steps date back to the time of Galileo Galilei (Froese 2006).Yet, the scientific basis for morphometry in fishes, and especially the mathematical way that weight relates to length, was set by Fulton, in 1906, who for the first time introduced fisheries science into 'allometry' (Froese 2006).Nowadays, the most commonly used relationships, that have been established for the majority of fishes (Binohlan & Pauly 2000, FishBase: www.fishbase.org:Froese & Pauly 2011), are those relating weight to body length (in the majority of cases, total body length (TL)), and different types of length (i.e., standard (SL) and fork (FL) length) to TL. Weight (W)-length (TL) relationships are of power type, i.e., W=a TL b .In this equation, a is the coefficient of body shape (Lleonart et al. 2000, Froese 2006, www.fishbase.org),and it gets values around 0.1 for fishes which are small sized and with a rounded body shape, 0.01 for streamlined-shaped fishes and 0.001 for eel-like shaped fishes.In contrast, b is the coefficient balancing the dimensions of the equation and its values can be smaller, larger or equal to 3 (Lleonart et al. 2000, Froese 2006, www.fishbase.org).In the first two cases (i.e., b<3 and b>3) fish growth is allometric (i.e., when b<3 the fish grows faster in length than in weight, and when b>3 the fish grows faster in weigth than in length), whereas when b=3 growth is isometric.Froese (2006) analyze 3929 weight-length relationships for 1773 species, and reports that b ranges between 1.96 and 3.94, with 90% of the cases falling inside the 2.7-3.4 range.The lowest values have been recorded for Cepola macropthalma, whereas the highest for Chaenocephalus aceratus.In principle, these types of relationships are allometric (82%), with a trend towards positive allometry (Froese 2006).Weight-length relationships are of high importance for fisheries science and can be used in a wide range of applications, such as: (a) estimation of biomass from length data; (b) estimation of a species condition factor; and (c) comparisons among life history and morphologic differentiations of the same species in different areas (e.g.,