411 Folia Zool. – 53(4): 411–416 (2004) Pilot study on the morphological identity of wild brown trout (Salmo trutta) stocks in the streams of the Danube river basin (Serbia) Saša MARIĆ*, Vera NIKOLIĆ and Predrag SIMONOVIĆ Institute of Zoology, Faculty of Biology, University of Belgrade, Studentski trg 16, 11001 Belgrade, Serbia and Montenegro; e-mail: sasa@bf.bio.bg.ac.yu Received 11 February 2003; Accepted 25 November 2004 A b s t r a c t . This study aimed to define the morphological characters useful to discriminate wild from stocked brown trout Salmo trutta in Serbia. Rainbow trout Oncorhynchus mykiss and Ohrid Lake’s belvica Salmothymus ohridanus were also examined as outgroup taxa in order to understand better the overall variability and to reduce bias in the methodology applied. Certain continuous external morphological characters were found useful to distinguish clearly the wild and stocked brown trout in particular streams. Molecular analysis is needed to validate this result, which could permit rapid field assessment and subsequent conservation of wild or stocked origin of as yet uninvestigated brown trout stocks in Serbia. Key words: aboriginality, field assessment, morphometrics, conservation Introduction Morphological variability in salmonid fishes has been extensively discussed both in Europe and worldwide. However, these studies used analytic approaches so out-of-date that they are no longer worthy of citation. Whereas, progress in biochemical and molecular methods has enabled the clear definition of distinct taxonomic and phyletic lineages of the brown trout Salmo trutta L., 1758, including the reconstruction of their evolutionary history. Within the recognized lineages, however, particular isolates remain insufficiently explained in a taxonomic sense as regards the discrepancy between morphological and molecular data. K o t t e l a t (1997) has denied the relevance initially given to taxonomic results based exclusively on biochemical and molecular data (i.e. ignoring information on morphology, zoogeography and dispersal). The genetic character and purity of brown trout stocks in Europe have received much attention in the last 30 years, with contradictory conclusions about the impact of stocking on the native brown trout populations (M o r à n et al. 1995, K r i e g & G u y o m a r d 1985). The main aim of the present study was to compare the morphology of wild and stocked brown trout in Serbia to determine whether there are any morphological characters in wild brown trout that can be used as a quick field criterion for determining the status (wild or stocked) of captured fish. Materials and Methods Specimens of brown trout Salmo trutta, rainbow trout Oncorhynchus mykiss and Lake Ohrid belvica Salmothymus ohridanus were collected in the 1998–2000 from the streams located in Eastern and Western Serbia and the former Yugoslav Republic of Macedonia. The fish were captured by electrofishing, angling and gill netting between May 1996 and October * Corresponding author