Proposed standard weight equations for brown
trout (Salmo trutta Linnaeus, 1758) and Barbus tyberinus Bonaparte, 1839 in the River Tiber basin (
Angeli Valentina , Bicchi Agnese, Carosi Antonella, Spigonardi Maria Pia, Pedicillo Giovanni, Lorenzoni Massimo.
Cellular and Environmental Biology University of Perugia, via Elce di Sotto
Abstract: Relative weight is an index of condition that provides a measure of the well-being of a fish population. The index is calculated on the basis of comparison between the actual weight of a specimen and the ideal weight of a specimen of the same species in good physiological condition (standard weight). Two methods forcalculating the standard weight are proposed in the literature: the RLP method and the EmP method. Although the RLP method is widely used, it has some limitations; as it uses the weights derived from the TL/W regressions of different populations to calculate the index, it is influenced by the size distribution of the specimens. The main aim of our research was to work out equations for calculating standard weight that would be valid for two species in the River Tiber basin. To this aim, 91 (N = 18216) different populations of brown trout (Salmo trutta L.) and 64 (N = 12778) different populations of Barbus tyberinus were examined. A further aim was to compare the validity of the two proposed methods (RLP and EmP) of calculating relative weight. For brown trout, the equations calculated with regard to the River Tiber basin are as follows: log10Ws = - 5.197 + 3.117 log10TL (RLP method); log10Ws = - 5.203 + 3.154 log10TL – 0.015 (log10TL)2 (EmP method), where TL is the total length. The equations calculated by means of the two methods for Barbus tyberinus in the River Tiber basin are as follows: log10Ws = – 5.072 + 3.040 log10 TL (log10 TL) (RLP method) and log10Ws = – 4.917 + 2.987 log10TL + 0.003 (log10TL)2 (EmP method).
Key words: Relative weight (Wr), index of condition, RLP method, EmP method, length-weight regression.