Life history and genetic characterisation of sea troutSalmo truttain the Adriatic Sea

Abstract

The brown trout Salmo trutta is characterised by both anadromous (sea trout)and resident populations, naturally occurring in Atlantic and Ponto-Caspian rivers. Sea trout are currently considered absent from rivers of the Mediterranean area, probably because of the non-optimal chemical-physical characteristics of the Mediterranean Sea. However, the occasional bycatch of smoltified S. trutta in the Adriatic Sea is well known among fishermen and the biological explanation of this phenomenon is still controversial. The aim of this study was to compare the genetic diversity of freshwater and marine brown trout to try to understand the factors underlying the presence of putative anadromous brown trout in the Adriatic Sea.2. In this study, we analysed the genetic diversity of: (1) wild brown trout collected from the Esino River (central Italy); (2) a domestic strain of brown trout used for stocking the study area; and (3) a sample of Adriatic sea trout collected near the outlet of the Esino River. Together with genetic analysis, we carried out scale analysis in order to track the freshwater/marine stages of the life cycle in the sea trout samples. The genetic characterisation was carried out by polymerase chain reaction-restriction fragment length polymorphism analysis of the mtDNA fragment ND-5/6 and the nuclear locus LDH-C1* and by genotyping 15 microsatellite loci. The genetic polymorphism obtained was used to investigate intra-and inter-population genetic diversity, rates of genetic introgression between wild and domestic samples and the origin of sea trout specimens by using assignment tests.3. Our genetic analyses demonstrated that the sea trout analysed in this study are from the domestic strain of Atlantic origin used in central Italy for stocking activities. The level of genetic introgression between native and domestic samples is high in the Esino River. The populations more resilient to introgressive hybridisation appeared to be those living in the portion of the river network dominated by carbonate rocks. Assignment tests (GeneClass) suggest the existence of a link between stocking efforts and the freshwater origin of the sea trout. In addition, data obtained from the analysis of scales, size measurement, and sex determination | 461 SPLENDIANI Et AL.

Molecular characterization of rare anadromous Rhône River brown trout

“…Because the Atlantic trout is not natural in the Rhône basin or in any Mediterranean river, it is most likely that these eight sea trout come from restocking. These results are similar to other molecular studies realized on sea trout from the Adriatic Sea; sea trout from this area were also assigned to stocked Atlantic strains from hatcheries (Snoj et al, 2002;Splendiani et al, 2020).…”

Conservation Genetics of Mediterranean Brown Trout in Central Italy (Latium): A Multi-Marker Approach

“…The MA lineage identifies, although not exclusively, Salmo marmoratus (Cuvier, 1829) that is endemic of the Alpine watersheds draining to the Northern Adriatic Sea [1,2]. Nevertheless, haplotypes from the MA lineage are also found in wild native populations of Mediterranean brown trout from rivers flowing into the central Adriatic (e.g., Fiastrone, Esino, Aterno), including a tributary of the Tronto river (i.e., the Fosso Tufo) [6,25,28,69] and, more recently, from Corsican rivers [70]. Therefore, to the best of our knowledge, the occurrence of MA haplotypes in Rapido (RAP) and Simbrivio (SIM2) rivers provides the first remarkable records of such lineage in drainage basins of the Italian peninsula flowing into the Tyrrhenian Sea, as well as in the Latium region.…”

“…This may indicate mito-nuclear discrepancy and asymmetric introgression between markers, as also suggested by the lack of correlation between haplotype richness and the observed degree of admixture (LDH-C1*90 frequency) across populations (Figure 2E). Such a mismatch may result from various non-mutually exclusive mechanisms: native females preferably mating with domestic males (non-random mating), different fitness and/or migratory behavior associated with lineages and sexes [28,84]. Anyhow, if empirically verified, this would imply an underestimation of the Atlantic component based on the mitochondrial DNA in wild admixed populations.…”

“…In brown trout, fragments of the mitochondrial non-coding Control Region (CR) and various microsatellite arrays have been commonly used to assess neutral genetic diversity across populations. Specifically, the former is primarily employed for the identification of relatively ancient lineages (as defined by [5]), while the latter are extensively used for assessing genetic population structure even at the fine spatial scale [25][26][27][28]. When combined, they provide a useful tool to determine the distinctiveness of populations [29].…”

Short‐term homeostatic regulation of blood/interstitial fluid Ca2+ concentration by the scales of anadromous sea trout Salmo trutta L. during smoltification and migration

“…To address this question, here the authors of this study exfoliated scales from wild sea trout following a protocol developed in zebrafish Danio rerio (Metz et al ., 2014; Pasqualetti et al ., 2012a; Sire et al ., 2000). They then used a non‐invasive, extracellular, scanning Ca 2+ ‐sensitive microelectrode (Kühtreiber & Jaffe, 1990; Smith et al ., 1999) to measure biotic Ca 2+ fluxes into and out of both sides of the scale under different calcemic challenges set to mimic the homeostatic extracellular fluid (ECF)‐[Ca 2+ ] stress that might be induced by a variety of environmental Ca 2+ concentrations [Ca 2+ ] encountered during smoltification (Hoar, 1988; Rutkovska et al ., 2019) and anadromous migration (Eldøy et al ., 2015; Ruokonen et al ., 2018; Splendiani et al ., 2020).…”