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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

The 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. [ABSTRACT FROM AUTHOR]

Unio, a freshwater mussel genus, has a low number of species in Tunisia, among them U. durieui, which is categorised as Endangered for conservation in IUCN Red List. The purpose of the study was to investigate morphological similarity and genetic relationships between samples of the genus Unio collected from rivers of the Ichkeul watershed. The collection includes three samples of U. ravoisieri, a single sample of U. durieui and a sample morphologically distinct from the first two, which could be a new 'species' discovered in the sampling area. Principal components analysis, based on eight morphological traits, separated the samples into three groups according to the 'species' and the variant form was found morphologically closer to U. ravoisieri than U. durieui. Analysis of genetic diversity has defined an extensive allozyme monomorphism. The Nei's standard genetic distance between U. ravoisieri and U. durieui, ranges from 0.5330 to 0.5881 and FST values vary between 0.93 and 0.98 and are highly significant. However, the genetic comparison between the variant form and U. ravoisieri samples showed no significant difference in allele and genotype frequencies, which supports the hypothesis that the new form is a phenotype of U. ravoisieri and not a separate species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

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Geographic and temporal genetic variation of allele frequencies at 21 isozyme loci were examined in two populations of common Pandora, Pagellus erythrinus (Linnaeus, 1758, Sparidae). Fishes were sampled from Western and Eastern Mediterranean basins off Tunisian coasts over one year at the beginning of each season. Analysis of genetic diversity showed a low level of heterozygosity for all populations (average He=0.052). Fixation indices reflected a significant departure from Hardy_Weinberg equilibrium with heterozygote deficiencies, slight spatial differentiation between both sampling localities (FST=0.003, P=0.017) and temporal genetic stability at seasonal and annual scales. Annual genetic variation was evaluated over a five-year period estimated indirectly from fish otoliths. Comparison of genetic diversity between year classes of both locations showed an increase of the He values concurrent with age, supporting the hypothesis of the high variance in individual reproductive success. Finally, our results suggest that the effective population size of Pagellus erythrinus is large and genetic drift is weak but variable, especially between successive adult year classes for both sampling locations. [ABSTRACT FROM AUTHOR]