Limited contribution of hatchery-produced individuals to the sustainment of wild marble trout (Salmo marmoratus Cuvier, 1829) in an Alpine basin.

Fish stocking constitutes a common management practice in freshwaters all over the world, to enhance fisheries or to support threatened fish populations. Pervasive detrimental effects may affect the real effectiveness of stocking programs. However, studies assessing the real impacts and relative contribution of stocked trout in wild populations are surprisingly few. The marble trout, Salmo marmoratus (Cuvier 1829), is a critically endangered sub-endemic salmonid in Northern Italy, and an iconic species for recreational fishing and conservation, also representing an emblematic case of species negatively affected by restocking. For instance, marble trout inhabiting the Toce River, the second largest tributary of Lake Maggiore, has been stocked with different hatchery congener trout belonging to the Salmo trutta complex (putative marble trout, Atlantic trout Salmo trutta Linnaeus 1758 and putative Mediterranean trout Salmo ghigii Pomini 1941) over the last decades. Using mitochondrial (D-loop) and nuclear (12 microsatellites and LDH-C1*) markers, we characterised the genetic variability and gene flow among the wild and hatchery individuals of marble trout of this basin, to investigate the effectiveness of stocking activities on the native residual population. Despite extensive hybridization of marble trout with non-native brown trout stocks was shown, the presence of individuals belonging to pure native stock has been detected as well. However, concerns could be advanced regarding its future persistence, due to climatic and hydraulic instabilities or loss of environmental heterogeneity. Moreover, despite ongoing yearly massive stocking activities, a negligible contribution of reared putative marble trout in the wild sample has been documented, suggesting that natural recruitment represents the greatest source of this wild population sustainment. Important adaptive differences between wild and domestic trout are present, likely due to the deleterious long-term effects of the close breeding system of hatcheries. Finally, possible implications for stocking management improvement have been discussed.

The Italian Alpine and Subalpine trouts: Taxonomy, Evolution, and Conservation.

During the last 150 years, the trout-culture industry focused on enhancing trout populations by stocking, in response to the growing anglers' demand and the habitat degradation associated to the rapid urbanization and hydropower development. The industrialized north of Italy, home to the Italian Alpine and subalpine trout populations, is the source of most of the revenues of the national trout-culture industry. Its rapid growth, and the massive introduction of non-native interfertile trouts eroded the genetic diversity of native lineages, leading to harsh confrontations between scientists, institutions, and sportfishing associations. We review here the state of the art of the taxonomy and distribution of the northern Italian native trouts, presenting both scientific results and historical documentation. We think the only native trouts in this region are Salmo marmoratus, widespread in this region, plus small and fragmented populations of S. ghigii, present only in the South-western Alps. We strongly recommend the interruption of stocking of domesticated interfertile non-native trouts in this area, and recommend the adoption of Evolutionary Significant Units for salmonid fishery management. We further propose future research directions for a sustainable approach to the conservation and ecosystem management of the fishery resources and inland waters of northern Italy.

Mediterranean swordfish (Xiphias gladius Linnaeus, 1758) population structure revealed by microsatellite DNA: genetic diversity masked by population mixing in shared areas.

BACKGROUND: The Mediterranean swordfish stock is overfished and considered not correctly managed. Elucidating the patterns of the Mediterranean swordfish population structure constitutes an essential prerequisite for effective management of this fishery resource. To date, few studies have investigated intra-Mediterranean swordfish population structure, and their conclusions are controversial. METHODS: A panel of 20 microsatellites DNA was used to investigate fine-scale population structuring of swordfish from six main fishing areas of the Mediterranean Sea. RESULTS: This study provides evidence to reject the hypothesis of a single swordfish population within the Mediterranean Sea. DAPC analysis revealed the presence of three genetic clusters and a high level of admixture within the Mediterranean Sea. Genetic structure was supported by significant F ST values while mixing was endorsed by the heterozygosity deficit observed in sampling localities indicative of a possible Wahlund effect, by sampling admixture individuals. Overall, our tests reject the hypothesis of a single swordfish population within the Mediterranean Sea. Homing towards the Mediterranean breeding areas may have generated a weak degree of genetic differentiation between populations even at the intra-basin scale.