Righi Tommaso, Fasola Emanuele, Iaia Mattia, Stefani Fabrizio, Volta Pietro
Water Research Institute - National Research Council (IRSA - CNR), Largo Tonolli, 50, 28922 Verbania Pallanza, VB, Italy.
Water Research Institute - National Research Council (IRSA - CNR), Via del Mulino, 19, 20861 Brugherio, MB, Italy.
Sci Total Environ. 2023 Sep 20;892:164555. doi: 10.1016/j.scitotenv.2023.164555. Epub 2023 Jun 1.
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.
放养鱼是世界各地淡水水域常见的管理措施，目的是增加渔业产量或支持受威胁的鱼类种群。普遍存在的有害影响可能会影响放流计划的实际效果。然而，评估放流的鳟鱼对野生种群的实际影响和相对贡献的研究却出奇地少。大理石鳟（Salmo marmoratus，居维叶，1829年）是意大利北部极度濒危的亚特有鲑科鱼类，是休闲渔业和保护工作的标志性物种，也是因再引入而受到负面影响的典型案例。例如，在过去几十年里，马焦雷湖第二大支流托切河中的大理石鳟被投放了不同孵化场培育的同属鲑科的鳟鱼（推定大理石鳟、大西洋鲑Salmo trutta Linnaeus 1758和推定地中海鳟Salmo ghigii Pomini 1941）。我们使用线粒体（D环）和核基因（12个微卫星和LDH - C1*）标记，对该流域野生和孵化场培育的大理石鳟个体的遗传变异性和基因流进行了表征，以研究放流活动对本地残留种群的有效性。尽管已表明大理石鳟与非本地褐鳟种群存在广泛杂交，但也检测到了属于纯本地种群的个体。然而，由于气候和水文不稳定或环境异质性丧失，其未来的存续可能令人担忧。此外，尽管每年都有大规模的放流活动，但在野生样本中，养殖的推定大理石鳟的贡献微乎其微，这表明自然繁殖是维持该野生种群的最大来源。野生鳟鱼和养殖鳟鱼之间存在重要的适应性差异，这可能是由于孵化场近亲繁殖系统的长期有害影响所致。最后，讨论了对放流管理改进的可能影响。
