Presence of Lactic Acid Bacteria in the Intestinal Tract of the Mediterranean Trout (Salmo macrostigma) in Its Natural Environment

Knowledge of the composition of the gut microbiota in freshwater fish living in their natural habitat has taxonomic and ecological importance. Few reports have been produced on the composition of the gut microbiota and on the presence of LAB in the intestines of freshwater fish that inhabit river environments. In this study, we investigated the LAB community that was present in the gastrointestinal tract (GIT) of Mediterranean trout (Salmo macrostigma) that colonized the Biferno and Volturno rivers of the Molise region (Italy). The partial 16S rRNA gene sequences of these strains were determined for the species-level taxonomic placement. The phylogenetic analysis revealed that the isolated LABs belonged to seven genera (Carnobacterium, Enterococcus, Lactobacillus, Lactiplantibacillus, Vagococcus, Lactococcus, and Weissella). The study of the enzymatic activities showed that these LABs could contribute to the breakdown of polysaccharides, proteins, and lipids. In future studies, a greater understanding of how the LABs act against pathogens and trigger the fish immune response may provide practical means to engineer the indigenous fish microbiome and enhance disease control and fish health.

Genotyping of Two Mediterranean Trout Populations in Central-Southern Italy for Conservation Purposes Using a Rainbow-Trout-Derived SNP Array

Mediterranean trout is a freshwater fish of particular interest with economic significance for fishery management, aquaculture and conservation biology. Unfortunately, native trout populations’ abundance is significantly threatened by anthropogenic disturbance. The introduction of commercial hatchery strains for recreation activities has compromised the genetic integrity status of native populations. This work assessed the fine-scale genetic structure of Mediterranean trout in the two main rivers of Molise region (Italy) to support conservation actions. In total, 288 specimens were caught in 28 different sites (14 per basins) and genotyped using the Affymetrix 57 K rainbow-trout-derived SNP array. Population differentiation was analyzed using pairwise weighted FST and overall F-statistic estimated by locus-by-locus analysis of molecular variance. Furthermore, an SNP data set was processed through principal coordinates analysis, discriminant analysis of principal components and admixture Bayesian clustering analysis. Firstly, our results demonstrated that rainbow trout SNP array can be successfully used for Mediterranean trout genotyping. In fact, despite an overwhelming number of loci that resulted as monomorphic in our populations, it must be emphasized that the resulted number of polymorphic loci (i.e., ~900 SNPs) has been sufficient to reveal a fine-scale genetic structure in the investigated populations, which is useful in supporting conservation and management actions. In particular, our findings allowed us to select candidate sites for the collection of adults, needed for the production of genetically pure juvenile trout, and sites to carry out the eradication of alien trout and successive re-introduction of native trout.

A comment on “Morphologic and genetic characterization of Corsican and Sardinian trout with comments on Salmo taxonomy” by Delling et al. (2020): protected Tyrrhenian trouts must be named

The introduction of the use of molecular data has caused debates on the taxonomy of Corsican and Sardinian trouts, also referred to as Tyrrhenian trouts (i.e. Salmo trutta, Salmo macrostigma, Salmo cettii). A recent study by Delling et al. (2020) (Morphologic and genetic characterization of Corsican and Sardinian trout with comments on Salmo taxonomy. Knowl Manage Aquat Ecosyst 421: 21) introduces important evidence regarding the taxonomy of these populations. However, their subsequent denomination as Salmo sp., that is, an undefined taxon, could have serious consequences on their future conservation management plans. Considering their threatened status, the Tyrrhenian trouts should be referred to as Salmo trutta until the ongoing taxonomic uncertainty can be unambiguously resolved. These populations must then be treated as an Evolutionary Significant Unit (ESU) or as an Operational Conservation Unit (OCU) for further conservation managements plans, as already done for other Mediterranean trout lineages.

The role of the south-western Alps as a unidirectional corridor for Mediterranean brown trout (Salmo trutta complex) lineages

The role of the south-western Alps as a corridor for Mediterranean trout (Salmo trutta complex Linnaeus, 1758) was evaluated in order to understand the influence of the last glacial events in shaping the spatial distribution of the genetic diversity of this salmonid. For this, the allochthonous hypothesis of a man-mediated French origin (19th century) of the Mediterranean trout inhabiting the Po tributaries in the Italian side of the south-western Alps was tested. A total of 412 individuals were analysed at the mitochondrial control region. The phylogenetic classification was carried out by using a Median-Joining Network analysis. Mismatch pair-wise analysis, molecular dating and Kernel density distribution analysis of the main mitochondrial lineages were evaluated to compare past demographic dynamics with the current spatial distribution of genetic diversity. The main outcomes resulted strongly in agreement with a biogeographic scenario where the south-western Alps acted as a unidirectional corridor that permitted the colonization of the upper Durance (Rhône River basin) by trout from the Po River basin. Therefore, the Mediterranean trout should be considered as native also along the Italian side of the south-western Alps and the allochthonous hypothesis should be rejected.

Pug-Headedness Anomaly in a Wild and Isolated Population of Native Mediterranean Trout Salmo trutta L., 1758 Complex (Osteichthyes: Salmonidae)

Skeletal anomalies are commonplace among farmed fish. The pug-headedness anomaly is an osteological condition that results in the deformation of the maxilla, pre-maxilla, and infraorbital bones. Here, we report the first record of pug-headedness in an isolated population of the critically endangered native Mediterranean trout Salmo trutta L., 1758 complex from Sardinia, Italy. Fin clips were collected for the molecular analyses (D-loop, LDH-C1* locus. and 11 microsatellites). A jaw index (JI) was used to classify jaw deformities. Ratios between the values of morphometric measurements of the head and body length were calculated and plotted against values of body length to identify the ratios that best discriminated between malformed and normal trout. Haplotypes belonging to the AD lineage and the genotype LDH-C1*100/100 were observed in all samples, suggesting high genetic integrity of the population. The analysis of 11 microsatellites revealed that observed heterozygosity was similar to the expected one, suggesting the absence of inbreeding or outbreeding depression. The frequency of occurrence of pug-headedness was 12.5% (two out of 16). One specimen had a strongly blunted forehead and an abnormally short upper jaw, while another had a slightly anomaly asymmetrical jaw. Although sample size was limited, variation in environmental factors during larval development seemed to be the most likely factors to trigger the deformities.

Morphological survey as powerful detection tool of pure and local phenotypes in Salmo trutta complex

The native Mediterranean trout populations in central Italy are at risk of extinction. Hybridization with the alien Atlantic trout represents one of the major threats to the species. The main aim of the research was to test the efficiency of morphological characterization in revealing alien trout introduction, pure lineages and local adaptations, in five watersheds of central Apennines (Italy). Data analysis was carried out for a total of 258 specimens already genetically identified. The results of the multivariate analysis, performed using 10 qualitative and 47 quantitative variables, revealed two distinct phenotypic groups and confirmed, at a morphological level, the genetic separation between Atlantic and Mediterranean trout. The morphological variables that play a key role in the discrimination of the Mediterranean trout were: (i) number of parr marks with striped pattern, (ii) adipose fin mainly with white color and without black spots, and (iii) number of black opercular spots, compared to the Atlantic trout. The geometric analysis revealed the importance of the spatial arrangements of spots on the fish flank and the shape of caudal peduncle in discriminating different Mediterranean populations. The information collected confirmed the powerful of morphological surveys in the screening of conservation status of wild trout populations.

Ecology and conservation of the Mediterranean trout in the central Apennines (Italy)

The Mediterranean brown trout (Salmo trutta complex) is one of the freshwater fish species complex at greater risk of extinction in the Mediterranean area. The introduction of alien invasive species and their interaction with the native fauna represent some of the major threats to the survival of this species. Currently, the genetic variability of the Mediterranean trout (Salmo trutta complex) is being compromised by the introgressive hybridization with the Atlantic trout (Salmo trutta Linnaeus, 1758). Therefore, it is necessary to gain further knowledge on genetic and demographic characteristics of Mediterranean trout populations, that, combined with environmental and angling data, will allow to undertake sound conservation strategies. The aims of the present study were to analyze: i) the demographic characteristics of the Mediterranean trout in seven central Apennine river basins where native populations are threatened by stocking with the domestic trout of north Atlantic origin; ii) the influence of both environmental parameters and different fishery management strategies on the status of native trout populations. The project focuses on 14 sites included in the Natura 2000 EU wide network of nature protection areas, established under the 1992 Habitat Directive. A total of 25 watercourses were investigated for a total of 32 sampling sites. A census of the fish fauna was carried out by electrofishing at each sampling location. Fish and environmental data were collected in spring and autumn 2014. The results obtained in the present research allowed us to detect the presence of three residual Mediterranean trout populations with a high degree of genetic integrity in the study area. The native trout populations were characterized by higher abundances and higher adult density values. Well-structured native populations with higher legal-size specimens density and poor body conditions in terms of relative weight were observed in the no-fishing areas, probably due to the presence of intraspecific competition phenomena. The environmental analysis confirmed the key role played by the geological characteristics of the central Apennines in shaping the introgression levels observed in the wild trout populations, while the recovery of the water quality appears decisive in the development of management strategies aimed at their conservation.