Risks to stocks of native trout of the genus Salmo (Actinopterygii: Salmoniformes: Salmonidae) of Serbia and management for their recovery.
Background. Insufficiently controlled stocking compromises the high diversity of wild trout stocks of Serbia. Native brown trout, Salmo cf. trutta Linnaeus, 1758, and Macedonian trout, Salmo macedonicus (Karaman, 1924), reveal remarkable diversity assessed using the mtDNA molecular markers, with the eight exclusive and several more widely spread haplotypes found in them. Four alien trout species and strains and one strain of Macedonian trout were introduced into the home areas of the native wild trout stocks in Serbia. In addition to them, wild trout stocks were also affected by farmed rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), and brook trout Salvelinus fontinalis (Mitchill, 1815), that regularly escape to streams, and from Ohrid trout, Salmo letnica (Karaman, 1924), and Arctic charr, Salvelinus alpinus (Linnaeus, 1758), stocked into streams and reservoirs. Risk of invasiveness that wild trout stocks are exposed to and their restoration were driving forces for this study. Materials and methods. Trout specimens from the Jerma River sampled in 2013 were additionally analysed for their mtDNA haplotype. The invasiveness potential of eleven alien trout species and strains introduced by stocking into wild brown- and Macedonian trout stocks in Serbia were assessed with the Fish Invasiveness Screening Kit (FISK). Results. Five of introduced trout species and strains were classified as having a high risk (sensu lato) and two of them as having a high risk (sensu stricto) of being (or becoming) invasive. Conclusion. Progressively rising and insufficiently controlled fishing and management with stocking of non-indigenous trout in wild brown trout stocks are the main current threats to the original diversity. Alien brown trout strains cross breed with native brown trout and incorporate into their stocks. Currently, feral rainbow-, brook-, and Ohrid trout reveal great invasive potential by naturalization in waters heavily stocked with them. The fisheries measures aiming to control and/or to eradicate alien strains of brown trout involve the restriction of stocking, landing of trout suspected as of alien strain or species, as well as the stringent control of stocking material used for the restorative stocking. They are mandatory, regarding the conservational dependence of wild brown trout stocks.