Mugilids fisheries of Tunisian coasts and lagoons

With its 1300 km coastline and 110 000 ha of coastal lagoons, Tunisia offers important resources to demersal and pelagic fisheries. Among all the exploited fish species in Tunisia, mugilids are the most widespread. They are known in temperate, subtropical and tropical regions, and occur both in coastal areas, lagoon ecosystems and inland waters. Six mugilids species have been inventoried in Tunisia. Their migratory behavior consists of moving back and forth between brackish and saline environment where they spend a large part of their life cycles. This behavior results in a peculiar high vulnerability to human pressure. Consequently, they require special attention from fisheries managers for sustainable catches. This study was based on the data from the national fishing and aquaculture directorate (DGPA) statistics, and comprised time series from 1995 to 2015. We looked for clear tendencies and correlations between harvest from the coastal sea and lagoons of the different coastal regions, in relation to recruitment in coastal marine waters. We focused on two species, i.e. Mugil cephalus and Liza aurata, which are best appreciated for local consumption and, therefore, most targeted by the fishery in Tunisia. The Tunisian lagoons show a decreasing trend in mugilids landings. This may be explained by the disturbance of migratory ways and the degradation of the coastal habitats, by the harvest of fry used for the inland water-stocking program, and by the multiplication of droughts. Particularly the latter strongly limits the migration of juveniles. The harvest in the coastal zones is relatively stable, follows perfectly the total national landings, with although a clear increase since 2011 as a result of uncontrolled illegal fishing. The negative correlation between the total harvests of mugilids in the coastal sea and coastal lagoon was highly significant (Pearson coefficient r = −0.702, p < 0.001)

Relationships between heterozygosity, growth parameters and age in the common pandora Pagellus erythrinus (Sparidae) in the Gabes Gulf (Tunisia)

International audienceThe relationship between heterozygosity and age, as well as growth-related traits, was explored in the common pandora Pagellus erythrinus, a sparid fish subjected to commercial exploitation in the Mediterranean Sea. Allozyme electrophoresis was used to quantify the levels of heterozygosity of 238 adult fish from 3 to 7 yr old, aged by means of otoliths and captured in the Gabes Gulf, located along the south-eastern coast of Tunisia. Analyses were conducted by using individual single-locus and multi-locus heterozygosity and 4 growth-related parameters-standard length, total body weight, otolith length and otolith weight-as well as 2 measures of condition (condition factor and relative condition factor). For the 4 growth-related parameters and 2 condition parameters analyzed at 8 polymorphic loci, heterozygotes had higher average values than homozygotes in 36 out of 48 comparisons. However, since these 6 biometric parameters are highly correlated, this proportion should not be considered globally as strong evidence of a heterozygosity-fitness correlation (HFC). Interpreting these data on a per parameter basis, only otolith weight appeared significantly and positively correlated with multi-locus heterozygosity. Thus, although there was evidence for HFC, it appeared relatively weak for the growth para meters analyzed and may have arisen by chance. The results we obtained relative to survival are more convincing. Although cohorts did not appear genetically differentiated and the whole sample did not display any internal structure after a Bayesian analysis with the STRUCTURE software, multi-locus individual heterozygosity was significantly and positively correlated with fish age. This suggests better survival of heterozygotes and establishes the presence of a heterozygosity-fitness correlation in the Tunisian population of the common pandora

intégration de données de génétique et de morphologie à différentes échelles climatiques et géographiques chez la moule d'eau douce en danger Unio durieui (Bivalvia: Unionidae) endémique du Nord de la Tunisie

International audienceThe freshwater mussel Unio durieui is a rare bivalve endemic to North African watersheds. Although this is an important species from an ecological and conservation perspective, information on its genetic diversity and population structure is lacking. Here, we combine geometric morphometric and molecular genetic analyses to characterize and evaluate the status of populations of this endangered species from four Tunisian watershed basins (Cap Bon, Ichkeul, Northwest and Mejerda River basins). By using a multiparameter approach, we sought to test the hypothesis that populations from these geographic regions could be considered as distinct management units. Shell outline shapes were assessed using elliptic Fourier analysis followed by linear discriminant analysis of principal components. Multivariate analysis applied on normalized Fourier coefficients showed highly significant differences in shell shape among the populations. Population genetic analysis based on inter-simple sequence repeats revealed low levels of diversity and high differentiation between the populations studied. Two groups of populations are clearly evident, thus separating samples from the Northwest from those from the other watersheds. Although there is no evidence for isolation by distance patterns, genetic and phenotypic diversity appeared significantly correlated with climatic variables. These findings suggest isolation by environment and the nominal species U. durieui may constitute two biological species. Conservation programme actions should consider this substructure in establishing effective recovery strategies for this endangered species.néan

Length-weight relationship and growth parameters of the commercial fish Pagellus erythrinus (Linnaeus, 1758) (Actinopterygii: Sparidae) from northern and southern Tunisia

Based on length, weight, and age data, we examined allometry and growth parameters for common pandora, Pagellus erythrinus, commercially collected seasonally from northern and southern Tunisian coasts in 2007. A total of 370 specimens (14–27.5 cm in length) were used to assess the allometric variation at seasonal scales. The slope b values (regression coefficient) of the length-weight relationship varied between 2.494 to 3.237, indicating (roughly) an isometric to negative allometric growth pattern. The allometric relationship, as a proxy for fish condition, seems to be affected by seasons and sex in the northern population, while only seasons seem to have a strong effect in the southern population, as indicated by ANOVA. The von Bertalanffy growth parameters were identified at L∞ = 34.076 and 28.017 cm, k = 0.153 and 0.150/year, and t0 = −1.922 and −3.961 years for the northern and southern sample, respectively

Phylogeography of the common pandora Pagellus erythrinus in the central Mediterranean sea. Sympatric mitochondrial lineages and genetic homogeneity

The distribution of the genetic diversity and the population structure of Pagellus erythrinus were analysed using mitochondrial control region sequences and cytochrome b restriction profiles in a total of 128 and 508 individuals, respectively, that were collected from 15 sampling sites in the central Mediterranean Sea and from one site in the Atlantic Ocean. No population genetic structure was detected within the central Mediterranean, and thus, the commonly recognised transition zones in the area do not seem to affect population connectivity. The comparison between the Mediterranean samples and the single Atlantic sample suggests weak differentiation between the two basins. Three mitochondrial lineages were identified, each including individuals from almost every sampling site. The haplotype and nucleotide diversity values, mismatch distribution and demographic parameters indicate that the sympatry of these lineages can be ascribed to a period of isolation followed by genetic divergence, population expansion and secondary contact, all of which are likely to be associated with climatic oscillations that occurred during the middle and late Pleistocene

Mugilids fisheries of Tunisian coasts and lagoons

International audienc

Influence of hydrodynamic connectivity on the genetic structure and gene flow of the common pandora Pagellus erythrinus

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Morphological and genetic characterization of the invasive rayed pearl oyster Pinctada imbricata radiata (Mollusca: Bivalvia: Pteriidae) populations from contrasting environments along the Tunisian coast

International audienceTo understand patterns of genetic and morphological variability, population structure and dispersal dynamics of the invasive bivalve Pinctada imbricata radiata (Leach, 1814) in Tunisian waters, we studied 200 individuals from five different sites (natural, polluted and/or subjected to environmental and anthropogenic pressures) using 10 enzymatic systems and six shell measurements. In this study, we attempt to elucidate the relationship between the spreading ability and the adaptive potential of the species under various environmental stresses. Fourteen putative enzyme-coding loci were resolved, six of which were polymorphic at the level of 99%. P. imbricata radiata maintains a relatively consistent level of polymorphism at the genetic markers studied, since 10% of individuals were heterozygous. The mean F IS value was positive and significant in two samples. However, the remaining samples collected from the disturbed marine sites (polluted, urban and lagoon areas) were at Hardy-Weinberg equilibrium. Highly significant genetic (mean F ST = 0.022, P < 0.001) and morphological (Wilks' lambda = 0.0814, approximate F 20, 627 = 35.484, P < 0.001) differentiations between samples were observed, with no evidence of isolation caused by geographic distance. However, the Mantel test performed between genetic and morphological distances revealed a significant correlation. Our results indicate that natural selection seems to have a greater influence on genetic differentiation in P. imbricata radiata than genetic drift. The combination of genetic and morphological data provided important theoretical information for determining the invasion mechanisms of the species

Phylogeography of the common pandora <i>Pagellus erythrinus</i> in the central Mediterranean Sea: sympatric mitochondrial lineages and genetic homogeneity

<div><p>ABSTRACT</p><p>The distribution of the genetic diversity and the population structure of <i>Pagellus erythrinus</i> were analysed using mitochondrial control region sequences and cytochrome <i>b</i> restriction profiles in a total of 128 and 508 individuals, respectively, that were collected from 15 sampling sites in the central Mediterranean Sea and from one site in the Atlantic Ocean. No population genetic structure was detected within the central Mediterranean and thus, the commonly recognized transition zones in the area do not seem to affect population connectivity. The comparison between the Mediterranean samples and the single Atlantic sample suggests weak differentiation between the two basins. Three mitochondrial lineages were identified, each including individuals from almost every sampling site. The haplotype and nucleotide diversity values, mismatch distribution and demographic parameters indicate that the sympatry of these lineages can be ascribed to a period of isolation followed by genetic divergence, population expansion and secondary contact, all of which are likely to be associated with climatic oscillations that occurred during the middle and late Pleistocene.</p></div

Absence of spatial genetic structure in common dentex (Dentex dentex Linnaeus, 1758) in the Mediterranean Sea as evidenced by nuclear and mitochondrial molecular markers.

The common dentex, Dentex dentex, is a fish species which inhabits marine environments in the Mediterranean and Northeast Atlantic regions. This is an important species from an ecological, economic and conservation perspective, however critical information on its population genetic structure is lacking. Most samples were obtained from the Mediterranean Sea (17 sites) with an emphasis around Corsica (5 sites), plus one Atlantic Ocean site. This provided an opportunity to examine genetic structuring at local and broader scales to provide science based data for the management of fishing stocks in the region. Two mitochondrial regions were examined (D-loop and COI) along with eight microsatellite loci. The COI data was combined with publicly available sequences and demonstrated past misidentification of common dentex. All markers indicated the absence of population genetic structure from the Bay of Biscay to the eastern Mediterranean Sea. Bayesian approaches, as well as the statistical tests performed on the allelic frequencies from microsatellite loci, indicated low differentiation between samples; there was only a slight (p = 0.05) indication of isolation by distance. Common dentex is a marine fish species with a unique panmictic population in the Mediterranean and likely in the Atlantic Ocean as well