Mediterranean Trout Research Articles

Flank spot number and its significance for systematics, taxonomy and conservation of the near-threatened Mediterranean trout Salmo cettii: evidence from a genetically pure population.

The number of spots on the flank of the Mediterranean trout Salmo cettii population from Tellesimo Stream in Sicily, Italy, varied between seven and 37, with a median and mode of 21, numbers much lower than those reported in the literature and different from those of other Italian trout populations. This finding could be ascribed to the phenotypic plasticity of the species or, alternatively, could provide evidence to support the different origin of Sicilian autochthonous trout. Given the ease of use of this character for the identification of native fish, it could be particularly important for conservation and management purposes.

The Effects of Paleoclimatic Events on Mediterranean Trout: Preliminary Evidences from Ancient DNA.

In this pilot study for the first time, ancient DNA has been extracted from bone remains of Salmo trutta. These samples were from a stratigraphic succession located in a coastal cave of Calabria (southern Italy) inhabited by humans from upper Palaeolithic to historical times. Seven pairs of primers were used to PCR-amplify and sequence from 128 to 410 bp of the mtDNA control region of eleven samples. Three haplotypes were observed: two (ADcs-1 and MEcs-1) already described in rivers from the Italian peninsula; one (ATcs-33) belonging to the southern Atlantic clade of the AT Salmo trutta mtDNA lineage (sensu Bernatchez). The prehistoric occurrence of this latter haplotype in the water courses of the Italian peninsula has been detected for the first time in this study. Finally, we observed a correspondence between frequency of trout remains and variation in haplotype diversity that we related with ecological and demographic changes resulting from a period of rapid cooling known as the Younger Dryas.

Territorial and foraging behaviour of juvenile Mediterranean trout under changing conditions of food and competitors

Territoriality is probably the most important ecological mechanism regulating densities in stream-living salmonids. Body size is typically regarded as the best predictor of territory size, but food abundance and competitor density may be key driving factors. However, a global analysis of literature data showed no clear patterns on the relative causal role of those factors on determining territory size in juvenile salmonids. Thus, in a factorial experiment, we estimated to what extent simultaneous variations of fish size, competitor density, and food abundance affected the size of foraging and defended areas of Mediterranean brown trout (Salmo trutta). In contrast with former studies, we found that foraging areas were larger than defended territories. Foraging and territorial behaviour changed significantly under varying density and feeding regimes. Foraging areas decreased with increasing competitor density and food availability, and there was a strong interaction between these two factors. Defended territories decreased with increasing density, irrespective of food abundance. Although our findings showed a significant allometric relationship between fish length and territory size, the data contained much unexplained variability. Our findings suggest that defended areas are relatively fixed for a given trout length. However, at extremely high population densities, defended areas decreased. Thus, under extreme competition, such as during critical periods right after emergence, trout may subdivide available habitat and thereby moderate density declines.

ENGLISH

Mediterranean river ecosystems have a highly endangered biodiversity;consequently, a monitoring activity is neededto identify the most impacted areas, the risk factors and to evaluate the efficacyof protection and restoring activities. This is particularly true for tributaries that are often overlooked by public agencies, while they are central elements for the protection of biodiversity. According to the Water Framework Directive (W.F.D.) this requires a multidisciplinary approach, linked to the study of the physicochemical, hydromorphological and biological characters of the water environments. In this study the results are reported of a monitoring activity in the Tellesimo Stream, a high quality Sicilian water course, wheretwo fish species included in the I.U.C.N. Red List as Critically Endangered (Anguilla Anguilla)and Near-Threatened (Salmo cettii) live. According to the WFD multidisciplinary approach, both a biological quality index (I.B.E.), using benthic macroinvertebrates as indicators, and a chemical-microbiological quality index (L.I.M.) were used. The two indexes gave different and sometimes contrasting results. This led to ascertaindifferent environmental risks for this stream: a seasonal (autumn) pollution, detected by I.B.E., probably due to the illegal discharge of olive mills waste water into the karst system, and a lighter but more chronicalteration, detected by L.I.M., probably due to theagricultural and/or small industrialactivities existingin the catchment area. These results highlight the need to use different methods to evaluate stream quality: in fact this allows the identification ofdifferent risk factors that sometimes can act in a very subtle or unseen way.

Semen Quality of Threatened Native Population of Mediterranean Brown Trout ( Salmo cettii , Rafinesque 1810) in the Biferno River (Molise Region - South Italy)

Semen Quality of Threatened Native Population of Mediterranean Brown Trout ( Salmo cettii , Rafinesque 1810) in the Biferno River (Molise Region - South Italy)

Morphological and genetic characterization of Sardinian trout Salmo cettii Rafinesque, 1810 and their conservation implications

The morphological and genetic structure of Western Mediterranean trout Salmo cettii inhabiting basins in Sardinia was completed to assist the design of its conservation programmes. Genetic analysis of protein-coding LDH-C1 plus sequencing mitochondrial control region gene and analyses of morphological characters described 253 specimens from seven localities in two basins in Southwest Sardinia. Nuclear and mitochondrial analyses revealed all of the fish were pure-bred native S. cettii, with no introgression from allochthonous S. trutta. The novel 18 mtDNA control region haplotypes were clustered in an ‘insular’ clade, strictly related to the Adriatic haplogroup, and depicted a radial network around two ancestral haplotypes. Completion of discriminant analysis using data on body pigmentation and quantitative morphologic parameters revealed three phenotypic groups within the fish. Each population and phenotype, characterised by high values of nucleotide and haplotype diversity, were not genetically differentiated and not geographically structured according to the two hydrological basins. Geometric morphometric analysis, based on 15 landmarkers, revealed pronounced and highly significant differences in body shape morphology between populations, suggesting S. cettii is locally adapting to extreme environmental conditions and so future management plans for these populations should treat the two basins as distinct morphological units.

Life+ Trout Project (LIFE12 NAT/IT/0000940) for the recovery and conservation of Mediterranean trout (Salmo trutta complex) in the central Apennines (Italy).

Life+ Trout Project (LIFE12 NAT/IT/0000940) for the recovery and conservation of Mediterranean trout (Salmo trutta complex) in the central Apennines (Italy).

The evolutionary jigsaw puzzle of the surviving trout (Salmo trutta L. complex) diversity in the Italian region. A multilocus Bayesian approach

Mediterranean trout populations display a diversity of phenotypes, representing a valuable model for the study of adaptation and a puzzling dilemma for taxonomists and biogeographers, which is further entangled by the widespread introgression of allochthonous genes.In this paper we analysed DNA polymorphism at multiple loci (sequence variation of the mitochondrial control region and eight nuclear fragments and length variation at eleven nuclear microsatellite loci) in representative samples of the autochthonous taxonomic diversity described in Italian trout populations (Salmo marmoratus, S. carpio, S. cenerinus, S. cettii and S. fibreni) and in samples from hatchery-originated strains of Atlantic S. trutta. We employed model-based clustering and Approximate Bayesian Computation in order to: (i) describe the phylogeographic structure of Italian autochthonous trout populations; (ii) evaluate a set of evolutionary/biogeographic models. The inclusion of hatchery-originated strains allowed to account for man-mediated allochthonous introgression in Italian populations.Our results (i) showed that the analysed sample consists of two main autochthonous evolutionary lineages, including the marble trout populations on one side (‘marble’ lineage) and the three peninsular populations of S. cettii, S. cenerinus and S. fibreni on the other side (‘peninsular’ lineage); (ii) indicated that S. carpio originated from a ‘peninsular’ population, with a possible, limited contribution from the ‘marble’ lineage; (iii) pointed out that the ‘marble’ lineage started diverging before the separation of the ‘peninsular’ lineage from Atlantic S. trutta; (iv) suggested that a model of divergence involving gene flow from the ‘peninsular’ population into the ancestral gene pool of ‘marble’ trout is most consistent with the genetic data; (v) provided evidence that the autochthonous trout gene pools in the Tyrrhenian and Adriatic basins of the Italian peninsula started diverging very recently (most likely after the last glacial maximum).

A new biological indicator to assess the ecological status of Mediterranean trout type streams

Fuelled by the generalized degradation of freshwater ecosystems, the development of tools to assess their ecological status has been the focus of intensive research in the last decades. Although fish are one of the key biological quality elements used to describe the ecological status of rivers, fish metrics that accurately respond to disturbances in Mediterranean trout type streams are still lacking. In these systems, multimetric indices are not optimal indicators because of their low species richness and abundances, thus alternative approaches are needed. Since carrying capacity defines the potential maximum abundance of fish that can be sustained by a river, its relationship with actual density (D/K ratio) could be an accurate indicator of population conservation status and consequently of the ecological status of the river. Based on this rationale, we modeled carrying capacity dynamics for 37 brown trout populations during a 12-year study period. We analyzed the response of the D/K ratio to a gradient of increasing environmental harshness and degradation in order to assess its suitability to accurately measure brown trout conservation status. Our results showed that the D/K ratio was highly sensitive to temporal and spatial variations in environmental conditions and the levels of human-induced environmental degradation. Variations in the environmental and human degradation factors included in the best explaining regression models developed for the whole population and by age classes accounted for between 58 and 81% of the variation in the D/K ratio. Likewise, the D/K ratio was sensitive to both general and life stage specific disturbance factors. Further analyses helped identify the factors limiting population abundance. Therefore, the D/K ratio could be an interesting indicator to consider when defining objective management plans and corrective actions in degraded rivers and streams subject to Mediterranean climatic conditions.

Fecundity, egg and alevin size in the River Irminio population of the threatened Salmo cettii Rafinesque-Schmaltz, 1810 (Sicily, Italy)

Summary This study reports the first available data on the reproductive biology of an Italian Salmo cettii trout population. Fecundity, egg and larvae size were determined in 38 females collected by electro-fishing before spawning (January–February, 1993 and 1994) in the River Irminio (SE Sicily, Italy; 36°57′36″N; 14°46′18″E), probably the southernmost trout river in Europe. The smallest ripe female was 16.3 cm long and the largest 31 cm (SL). Fecundity was described according to: Log F = −0.669 + 2.592 × Log SL, which is comparable to the most fecund European trout populations. This can be explained by the productivity of this river: on the basis of the results it was not possible to use fecundity to discriminate between nominal brown trout and Mediterranean trout (i.e. no taxonomic fecundity differences were found) nor to show clear-cut differences in fecundity between Atlantic and Mediterranean habitats. Bigger females produced significantly larger eggs, which in turn produced significantly longer alevins at hatch. This significantly positive relationship was still present after 15 days and at the resorption of the yolk sac. The interplay between high fecundity and large egg diameter (i.e. high allocation in egg mass) could be particular to this trout, and produced very high GSI values that showed no significant relationship to length. The data reported in this study are particularly important for the design and implementation of effective management and conservation measures for this threatened trout species.

Population and family structure of brown trout, Salmo trutta, in a Mediterranean stream

The physical arrangement of closely related individuals is expected to significantly influence the pattern of population genetic structure. For example, if related individuals are non-randomly distributed and included in samples, this may lead to exaggerated conclusions about genetic differentiation. In the present study, we compared population structure v. family relationships of brown trout (Salmo trutta L.) along a Mediterranean stream (Pyrenees) by using eight microsatellite loci. Results showed low levels of genetic (FST) differentiation between collections in a 6.5-km transect along the stream, and a significant correlation between genetic and geographical distance matrices, indicating a weak population structure associated with spatial distribution. Our data also indicated that geographical proximity of related individuals in the youngest (0+, 1+) cohorts probably was associated with limited dispersal of younger brown trout from spawning redds. Family relationships provided evidence, however, for movement of adult trout over distances of a few kilometres that probably contributed to the low observed differentiation. Dispersal of adult Mediterranean trout contrasts with the clustering of related older trout observed for some north European rivers and could be related to the reduced productivity in southern stream basins.

Stocking of native Mediterranean brown trout (Salmo trutta) into French tributaries of Lake Geneva does not contribute to lake‐migratory spawners

Abstract – We studied the contribution of stocking with Mediterranean autochthonous brown trout (Salmo trutta) to the lake‐migratory spawners in French tributaries of Lake Geneva. This singular lake system is inhabited by both the resident and the migratory life‐history form, and by trout of Atlantic and Mediterranean origins. Using two discriminatory microsatellite loci between the Atlantic and Mediterranean alleles, we compared the genetic composition of the migratory Atlantic populations of the four main tributaries before (1999; N = 113) and after (2004, 2005 and 2006; N = 137) recent introductions of native Mediterranean trout. No significant modification of the genetic composition was detected in all four populations over time and only two individuals were statistically assigned to the Mediterranean strain by the Bayesian method implemented in the structure program. These results suggest a negligible contribution of the stockings with autochthonous Mediterranean trout to the lake‐migratory spawners migrating into the four tributaries.

Geometric morphometrics reveals sexual and genotypic dimorphisms in the brown trout

The objective is to study different factors of variations in the body shape of trout (Salmo trutta ) belonging to the Mediterranean lineage (indigenous trout) or Atlantic lineage (introduced trout), and their hybrids. Using thin plate-spline (TPS) method by pointing landmarks, it made possible to provide a graphical representation of the characteristic conformation of the individuals. The characteristics of form highlighted let appear – that the male trout have a dorsal part more prominent than that of the female trout and a larger head – the existence of a general curvature of the body related to the size of trout, independently of the sex. In addition, characteristics of form provide satisfactory results to distinguish the Mediterranean lineage from the Atlantic lineage. The recognition of hybrid trout is more random because very near to Mediterranean trout. The existence of a sexual dimorphism could be established in spite of the absence of information on the sex. Comparative with the sexual dimorphisms in spawning period reveals morphological transformations during the reproduction, mainly for the males. Independently of the genotypic and sexual dimorphisms, a general curvature of the body related to the size was detected.

Historical biogeography of Mediterranean trout

Complete sequencing of the mitochondrial control region was used to describe phylogenetic relationships of brown trout populations ( Salmo trutta) in the Mediterranean river basins of Iberia and to review the historical biogeography of trout from the Mediterranean regions. Phylogenetic relationships among trout lineages suggested that the Danubian one is the most ancestral, in accordance with the eastern origin of most of the European freshwater fish species. Nested-clade and mismatch analyses suggested that the present distribution of haplotypes of the Adriatic and Mediterranean lineages resulted from population expansions originated, respectively, from central and western Europe, which favoured extensive secondary contacts between lineages. Reduced diversity detected within 50% of the analysed populations and large intrabasin differentiation indicated restricted gene flow in post-glacial periods.