Kelig Mahe

Calcein and manganese experiments for marking the shell of the common cockle ( Cerastoderma edule ): tidal rhythm validation of increments formation

This work focuses on investigating the potential of calcein and manganese as growth markers of the common cockle (Cerastoderma edule) in the bay of Somme (France). Recapture of shells, previously marked using a chemical marking and then bred in natural conditions, was performed in order to determine the shell growth patterns. Calcein marking has shown a fluorescent increment in shells after only 30 min immersion time at 150 mg L −1 ,b ut also for shells immersed 3ha t 50 mg L −1 . Likewise, manganese shell marking was revealed under cathodoluminescence for shells immersed 1ha t 120 mg L −1 as well as for shells which spent 4 h at 90 mg L −1 . A numerical analysis per- formed on each marked cockles has revealed 23 micro-increments between the mark and the ventral edge of the valves, corresponding to the 23 tides that occurred during the 12 days at liberty post marking. The periodicity of increment formation is thus validated for a tidal frequency. The growth rates of C. edule, ranged from 11.67 to 19.94 μ md −1 , decreased significantly with increasing shell length. This preliminary study gives a clue to the understanding of cockle growth and could be used in shellfish production for cockle age monitoring, but also for chemical analysis to learn more about biomineralization process of this species.

Are red mullet efficient as bio-indicators of mercury contamination? A case study from the French Mediterranean

Mercury (Hg) is one of the main chemicals currently altering Mediterranean ecosystems. Red mullet (Mullus barbatus and M. surmuletus) have been widely used as quantitative bio-indicators of chemical contamination. In this study, we reassess the ability of these species to be used as efficient bio-indicators of Hg contamination by monitoring during 18 months Hg concentrations in muscle tissue of mullet sampled from 5 French Mediterranean coastal areas. Mean concentrations ranged between 0.23 and 0.78 μg g(-1) dry mass for both species. Values were consistent with expected contamination patterns of all sites except Corsica. Results confirmed that red mullets are efficient bio-indicators of Hg contamination. Nevertheless, the observed variability in Hg concentrations calls for caution regarding the period and the sample size. Attention should be paid to environmental and biologic specificities of each studied site, as they can alter the bioaccumulation of Hg, and lead to inferences about environmental Hg concentrations.

Sagittal otolith morphogenesis asymmetry in marine fishes

This study investigated and compared asymmetry in sagittal otolith shape and length between left and right inner ears in four roundfish and four flatfish species of commercial interest. For each species, the effects of ontogenetic changes (individual age and total body length), sexual dimorphism (individual sex) and the otoliths location on the right or left side of the head, on the shape and length of paired otoliths (between 143 and 702 pairs according to species) were evaluated. Ontogenetic changes in otolith shape and length were observed for all species. Sexual dimorphism, either in otolith shape and length or in their ontogenetic changes, was detected for half of the species, be they round or flat. Significant directional asymmetry in otolith shape and length was detected in one roundfish species each, but its inconsistency across species and its small average amplitude (6·17% for shape and 1·99% for length) suggested that it has barely any biological relevance. Significant directional asymmetry in otolith shape and length was found for all flatfish species except otolith length for one species. Its average amplitude varied between 2·06 and 17·50% for shape and between 0·00 and 11·83% for length and increased significantly throughout ontogeny for two species, one dextral and one sinistral. The longer (length) and rounder otolith (shape) appeared to be always on the blind side whatever the species. These results suggest differential biomineralization between the blind and ocular inner ears in flatfish species that could result from perturbations of the proximal-distal gradient of otolith precursors in the endolymph and the otolith position relative to the geometry of the saccular epithelium due to body morphology asymmetry and lateralized behaviour. The fact that asymmetry never exceeded 18% even at the individual level suggests an evolutionary canalization of otolith shape symmetry to avoid negative effects on fish hearing and balance. Technically, asymmetry should be accounted for in future studies based on otolith shape.

Comparing growth in surface and cave morphs of the species Astyanax mexicanus : insights from scales

BackgroundLife in the darkness of caves is accompanied, throughout phyla, by striking phenotypic changes including the loss or severe reduction in eyes and pigmentation. On the other hand, cave animals have undergone constructive changes, thought to be adaptive, to survive in this extreme environment. The present study addresses the question of the evolution of growth in caves, taking advantage of the comparison between the river-dwelling and the cave-dwelling morphs of the Mexican tetra, Astyanax mexicanus.ResultsA sclerochronology approach was undertaken to document the growth of the species in these two very distinct habitats. Scales from 158 wild Astyanax mexicanus specimens were analyzed from three caves (Pachón, Tinaja and Subterráneo) and two rivers (Rio Gallinas and Arroyo Lagarto) in San Luis Potosi and Tamaulipas, Mexico. A 10–13% reduction in scales size was observed in the cave morphs compared to the surface morphs. Age could be reliably inferred from annual growth increments on the scales from the two morphs of the species. Further comparisons with growth curves in laboratory conditions, obtained using the von Bertalanffy growth model, were also performed. In the wild and in the laboratory, cavefish originating from the Pachón cave reached smaller sizes than surface fish from three different locations: Rio Gallinas and Arroyo Lagarto (wild sampling) and Texas (laboratory population), respectively. Wild Pachón cavefish also seemed to grow to smaller sizes than the two other wild cavefish populations studied, Tinaja and Subterráneo. Finally, growth in the laboratory was faster than in the wild, particularly in the two first years of life.ConclusionsThese data suggest that cavefish originating from the Pachón cave are subjected to an intrinsic limitation of their final size, which is at least in part independent from energy/food availability. This growth limitation may be an advantageous way of limiting energy expenditure and food needs in the cave environment. Moreover, growth regulation evolved differently in independently evolved cave populations. These results are discussed with regard to the sources of energy or general ecological conditions present in caves, and to the differences in behavior or feeding skills known in cavefish.

Black scorpionfish Scorpaena porcus (Scorpaenidae): a first record in the eastern English Channel

This is the first record of the black scorpionfish Scorpaena porcus being found in the eastern English Channel. A specimen was caught on 15 October 2012 off the port of Courseulles-sur-mer. It measured 31.6 cm and weighted 800 g. From a study of its sagittal otolith, this specimen appeared to be 9 years old.

Morphological variability of the shape of striped red mullet Mullus surmuletus in relation to stock discrimination between the Bay of Biscay and the eastern English Channel

Truss analysis and length measurements were made on 168 striped red mullet Mullus surmuletus. Multivariate statistical analyses with principal component analysis and partial redundancy analysis (pRDA) were used on these measurements to evaluate the influence of maturity, sex and geographical area distribution on body shape. Truss measurements were important to quantify and discriminate changing body shape, presumably due to changing environmental conditions. Sexual dimorphism was not observed and juveniles could be distinguished from adults based on their body shape. More importantly, M. surmuletus occurring in different geographical areas could be differentiated using this method. Based on pRDA, a significant difference of head morphological dimensions was observed between populations occurring in the eastern English Channel and those occurring in the Bay of Biscay, suggesting that fish from these areas could represent two subpopulations.

Variability of PCB burden in 5 fish and sharks species of the French Mediterranean continental slope.

Despite being generally located far from contamination sources, deep marine ecosystems are impacted by chemicals like PCB. The PCB contamination in five fish and shark species collected in the continental slope of the Gulf of Lions (NW Mediterranean Sea) was measured, with a special focus on intra- and interspecific variability and on the driving factors. Significant differences occurred between species. Higher values were measured in Scyliorhinus canicula, Galeus melastomus and Helicolenus dactylopterus and lower values in Phycis blennoides and Lepidorhombus boscii. These differences might be explained by specific abilities to accumulate and eliminate contaminant, mostly through cytochrome P450 pathway. Interindividual variation was also high and no correlation was observed between contamination and length, age or trophic level. Despite its major importance, actual bioaccumulation of PCB in deep fish is not as documented as in other marine ecosystems, calling for a better assessment of the factors driving individual bioaccumulation mechanisms and originating high variability in PCB contamination.

Habitat discrimination of big-scale sand smelt Atherina boyeri Risso, 1810 (Atheriniformes: Atherinidae) in eastern Algeria using somatic morphology and otolith shape

Abstract Somatic morphology and otolith shape were used to discriminate four samples of Atherina boyeri from three different habitats: Mellah lagoon (n = 269), Annaba Gulf (144 punctuated and 194 unpunctuated individuals) and Ziama inlet (n = 147) in eastern Algeria. For each individual, somatic morphology was described with 13 metrics and eight meristic measurements, while the otolith contour shape of 452 individuals from the three habitats was analysed using Fourier analysis. Then, two discriminant analyses, one using the 13 metric measurements and the other using Fourier descriptors, were used in order to discriminate populations of A. boyeri. The results of the discriminant analyses based on the two methods were similar, and showed that this species could be discriminated into three distinct groups: (1) marine punctuated, (2) lagoon and marine unpunctuated and (3) estuarine. These results are consolidated by the comparison of the Mayr, Linsley and Usinger coefficient of difference for the meristic parameters according to the location origin, where the difference reached a racial or even sub-specific level for some characters, depending on which pairs of populations were compared.

Otolith growth and age estimation of bastard grunt, Pomadasys incisus (Actinopterygii: Perciformes: Haemulidae), in the Gulf of Tunis (Central Mediterranean)

Background. Bastard grunt, Pomadasys incisus (Bowdich, 1825), is reported as a well-established species in the Mediterranean Sea. Although bastard grunt has rapidly expanded its area of distribution in the Mediterranean, there is no information about its age and growth. The aim of this study was to provide data about growth, condition, and first sexual maturity of the species in order to contribute to a better management of its fishery. Materials and methods. A total of 515 specimens of bastard grunt were caught in the Gulf of Tunis. The age was determined from otoliths. Length–weight relation, von Bertalanffy equation, and growth rate were employed to evaluate the fish growth. Also the condition factor and length at first sexual maturity were calculated. Results. In the Gulf of Tunis population, females were significantly predominant and the overall sex ratio (M : F) reached the value of 1 : 2.17. The two sexes showed a positive allometric growth. The marginal increment analysis validated the annual deposition of one single annulus in the winter. Growth in (total) length (TL) was approximately 65% during the first year of life. The von Bertalanffy growth equation was TL = 23.9 × (1 – e–0.186 × (t + 4.62)). The somatic condition of fish increased markedly during the late spring and summer. Length at first sexual maturity of the bastard grunt was 16.6 cm for males and 16.8 cm for females, which correspond to an age of about 2 years. Conclusion. The rapid growth during the first year of life, the early maturity and the moderately short life cycle contribute to the relatively fast spreading of the species.

Evidence of a relationship between weight and total length of marine fish in the North-eastern Atlantic Ocean: physiological, spatial and temporal variations

Weight–Body Length relationships (WLR) of 45 fish species (37 Actinopterygii and eight Elasmobranchii) were investigated. A total of 31,167 individuals were caught and their biological parameters measured during the four quarters from 2013 to 2015, on five scientific surveys sampling the North-eastern Atlantic Ocean from the North Sea to the Bay of Biscay (ICES Divisions IVb, IVc, VIId, VIIe, VIIg, VIIh, VIIj, VIIIa and VIIIb). Among 45 tested species, all showed a significant correlation between total length (L) and total weight (W). The influence of sex on WLR was estimated for 39 species and presented a significant sexual dimorphism for 18 species. Condition factor (K) of females was always higher than for males. Moreover, a spatial effect on the WLR according to five ecoregions (the Bay of Biscay, the Celtic Sea, the Western English Channel, the Eastern English Channel and the North Sea), was significant for 18 species among 38 tested species. The temporal effect was tested according to components (year and quarter/season). The seasonality effect on WLR is more frequently significant than the year especially for the Elasmobranchii species, and can be related to the spawning season. Finally, depressiform species (skates, sharks and flatfish) are characterized by positive allometric growth, whereas there is no such clear pattern regarding roundfishes growth, whatever their body shape is.