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Advances in modeling growth using tag-recapture data and progress in otolith ageing procedures allowed improved fitting of the Western Atlantic bluefin tuna growth curve. Growth parameters were derived from an integrated analysis of tag-recapture data and otolith age-length data using the “Aires-da-Silva-Maunder-Schaefer-Fuller with correlation” (AMSFc) framework, which models growth such that parameter estimates from each data source are directly comparable. The otolith data consisted of a sample of 4045 otoliths for which ages were estimated using tested and consistent protocols and conventions designed to avoid bias. Strict data quality control measures were applied to the tagging data for quality assurance and a subsample of 1118 records were retained for use in the analysis. Two forms of the Schnute growth model were considered: the Richards model and the von Bertalanffy model. The Richards curve appears to provide a better fit. Both curves follow a similar trajectory until age 16, after which they diverge considerably. The Richards model supports a lower mean asymptotic length ( L ∞ = 271.0 cm FL) than the model currently used in the stock assessment ( L ∞ = 314.9 cm FL). [ABSTRACT FROM AUTHOR]

Environment-recruitment relationships can be difficult to delineate with parametric statistical models and can be prone to misidentification. We use non-parametric time-series modeling which makes no assumptions about functional relationships between variables, to reveal environmental influences on early life stages of bluefin tuna and demonstrate improvement in prediction of subsequent recruitment. The influence of sea surface temperature, which has been previously associated with larval growth and survival, was consistently detected in recruitment time series of bluefin tuna stocks that spawn in the Mediterranean Sea, the North Pacific, and the Southern Ocean. Short time series for the Gulf of Mexico stock may have precluded a clear determination of environmental influences on recruitment fluctuations. Because the non-parametric approach does not require specification of equations to represent system dynamics, predictive models can likely be developed that appropriately reflect the complexity of the ecological system under investigation. This flexibility can potentially overcome methodological challenges of specifying structural relationships between environmental conditions and fish recruitment. Consequently, there is potential for non-parametric time series modeling to supplement traditional stock recruitment models for fisheries management. [ABSTRACT FROM AUTHOR]

We investigated the habitat utilization, vertical and horizontal behaviour of Atlantic bluefin tuna Thunnus thynnus (ABFT) in relation to oceanographic conditions in the northwestern Mediterranean Sea, based on 36 pop-up archival tags and different environmental data sets. Tags were deployed on early mature ABFT (127–255 cm) between July and November in 2007-2014, on the shelf area off Marseille, France. The data obtained from these tags provided 1643 daily summaries of ABFT vertical behaviour over 8 years of tag deployment. Based on a hierarchical clustering of this data, we could identify four principle daily vertical behaviour types, representing surface ( ≦ 10 m ) and subsurface (10–100 m) orientation, moderate (50–200 m) and deep ( ≧ 200 m ) diving behaviour. These vertical behaviour types showed seasonal variations with partly opposing trends in their frequencies. Accordingly, ABFT were more surface orientated during summer, while moderate diving behaviour was more common during winter. Depth time series data further revealed inverted day-night patterns for both of these periods. Tagged ABFT frequented the surface waters more regularly during daytime and deeper waters during the night in summer, while the opposite pattern was found in winter. Seasonal changes in the vertical behaviour of ABFT were accompanied by simultaneous changes in environmental conditions (SST, chla, thermal stratification). Accordingly, surface orientation and moderate diving behaviour appeared to be triggered by the thermal stratification of the water column, though less pronounced than previously reported for ABFT in the North Atlantic, probably indicating adaptive vertical behaviour related to the availability of epipelagic food resources (anchovies and sardines). Deep diving behaviour was particularly frequent during months of high biological productivity (February-May), although one recovered tag showed periodic and unusual long spike dives during summer-autumn, in relation to thermal fronts. Regional effects on the vertical behaviour of ABFT were identified through GAMs, with surface orientation being particularly pronounced in the Gulf of Lions, highlighting its suitability for an ongoing annual aerial survey program to estimate ABFT abundance in this region. In addition, increased levels of mesoscale activity/productivity (e.g. related to oceanic fronts) were detected in an area regularly utilized by ABFT, south of the Gulf of Lions, underlining its attractiveness as foraging ground. Kernel densities of geolocation estimates showed a seasonal shift in the horizontal distribution of ABFT from this “high-use” area towards the Gulf of Lions during summer, probably linked to the enhanced availability of epipelagic food resources at this time. [ABSTRACT FROM AUTHOR]

The Atlantic Bluefin tuna (BFT, Thunnus thynnus ), one of the largest top-predator fish inhabiting the pelagic ecosystems of the North Atlantic Ocean and Mediterranean Sea, has been extensively overexploited in recent decades. However, in the Mediterranean Sea, the mixing rates between the eastern, central and western basins have not yet been fully and finally resolved. To date electronic tagging, otolith and genetic markers cannot still disentangle the pattern of tuna movements and population structuring in the basin, essential background for a proper management of BFT fisheries. Here, we used Expressed Sequence Tag-linked (EST-linked) microsatellites to explore population dynamics and adaptive evolution of Mediterranean T. thynnus. For this purpose, 16 EST-linked microsatellites were genotyped in 177 tuna individuals from the Mediterranean Sea and several methods were used to explore population genetic structuring and estimate/detect signals of local adaptation. Bayesian clustering results indicated the presence of a single cluster, corroborated also by the Correspondence Analysis and pairwise F STs . Similarly, the two methods used for the detection of outlier loci (LOSITAN and BayeScan), did not reveal any pattern suggesting the presence of selective pressure on the EST Simple Sequence Repeat (SSR) used. Our results suggest that the low level of polymorphism detected in this study could be ascribed to the presence of relatively conserved regions flanking these microsatellites. These genomic regions are probably not involved in physiological responses to local adaptation. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna ( Thunnus thynnus ) undertake extensive migrations throughout the North Atlantic Ocean, but spawn primarily in the Gulf of Mexico (GOM) and the Mediterranean Sea. Little is known about larval bluefin tuna (BFT) dynamics and growth despite numerous surveys conducted in the GOM. In this study, we describe age-length relationships for larval BFT using otolith increment analysis and compare somatic daily growth as revealed by individual increment widths from the GOM. Otoliths (sagittae) were aged from pre and post flexion larvae collected during multiple spring spawning seasons in 2000–2012 (259 larvae, 2.1–10.9 mm body length, 0–15 daily increments). For the first time, larval growth from the GOM is compared to historical larval collections in the neighboring Straits of Florida and in the Balearic Sea. Our results indicate that growth for GOM larvae is significantly faster than reported from previous studies, indicating different growth strategies during the larval stages for the two spawning grounds. This new growth curve will be incorporated into the calculations of the annual larval index used in the management of this overfished species. Growth and its variability, are important drivers, integral in studies of larval ecology dynamics for BFT. [ABSTRACT FROM AUTHOR]

Background: Elucidating the patterns of the Atlantic Bluefin tuna [ABFT, Thunnus thynnus (Linnaeus, 1758)] population structure constitutes a challenging task of great importance. Most of the unique challenges stem from its biology, as well as the attributes of the marine realm in which it disperses. Accurate information is urgently needed for stock assessment, and the identification of critical features to the persistence and adaptation of populations in order to formulate and adopt effective strategies for ABFT conservation and management. Conclusions of a great number of ABFT genetic studies on the Mediterranean Sea stock structure are rather controversial and not yet conclusive. In this study, ABFT genomic diversity was investigated in the Mediterranean Sea, which is the most important area for the species' reproduction. Results: Analyzing genome-wide SNPs and microsatellites from ABFT samples collected throughout the Mediterranean Sea did not provide strong evidence of genetic structure, pointing towards the existence of a single panmictic unit. An alternative view would recognize a failure to reject the null hypothesis of a panmictic unit as an effect of the study's sampling design, the type of markers used, and the effectiveness/suitability of analysis methods in respect to the species biological characteristics or any combination of the above. Conclusions: Unravelling the drivers of ABFT population diversity would require the consideration of important aspects of the species spawning behavior for the determination of the appropriate sampling design. Novel approaches and methods of analysis that will bring together experts in genetics/-omics, ecology and oceanography are deemed necessary. Analyzing ABFT genetic data under the discipline of seascape genetics could provide the analysis framework under which major abiotic and biotic forces controlling ABFT recruitment could be identified, elucidating the complicated population dynamics of the species, while multiple and continuous fisheries monitoring should in all cases be considered as a prerequisite in order to achieve efficient and long-term ABFT conservation. [ABSTRACT FROM AUTHOR]

From April to June Atlantic bluefin tuna, Thunnus thynnus, migrate along the western Sardinian coastline in a southward direction, where they are intercepted by the trap fishery. Fishermen claim that Mistral episodes facilitate the entry of tuna schools towards the traps, thus increasing capture rates. To test the fishermen’s hypothesis we conducted underwater visual counts of tuna in the trap chambers and analysed these data under the effect of wind. The results indicate a “stair-step” pattern in the abundance of tuna, demonstrating that major increases in abundance are associated with the Mistral. The second analytical approach involved a longer time scale to test whether higher Mistral occurrences corresponded to periods when higher captures were recorded. Using a linear regression model we found a significant correlation (p < 0.01) between catches and the wind speed class ≤ 15 knots. We hypothesize that the wind-driven current may produce favourable conditions for tuna migration and could play a significant role in enabling fish to save energy. It was also noted that the wind speed class > 15 knots seemed to have a negative effect on captures. This pattern may be caused by wind-induced advection of coastal waters generating a physical boundary that may have had a deterrent effect on tuna schools.

Numerosos estudios han sido enfocados a los ingredientes naturales para mantener la calidad y la vida útil de los alimentos. Los ingredientes biodegradables, tales como hidrocoloides y proteínas pueden ser utilizados para cubrir filetes de pescado con el objetivo de suprimir los cambios de calidad durante el almacenamiento en congelación. En la actualidad se han venido desarrollando empaques comestibles, como el glaseado con hidrocoloides, (gelatina, carragenina), que además de cumplir sus funciones como película protectora del alimento, son económicos, pueden ser ingeridos por el consumidor sin riesgo de toxicidad, ayudan a preservar las características organolépticas del producto, proporcionar características nutricionales y, por ser biodegradables contribuyen a la conservación del ambiente. El objetivo del presente estudio fue evaluar la incorporación de hidrocoloides al glaseado de lomos de atún como una alternativa de empaque. Cortes de atún fueron glaseados incorporándole soluciones de carragenina 0,05, y 0,15%, y gelatina al 0,5, 1%. Los cortes fueron de 15 cm3, congelados a -30ºC y glaseados con los tratamientos mencionados sumergiéndose la muestra de atún en las soluciones a 0 ºC por 30 segundos y luego almacenados a -10ºC por 0, 15 y 30 días. Los resultados del análisis proximal, las proteínas solubles, rancidez oxidativa, y color mostraron que todas las muestras glaseadas con hidrocoloides mantienen sus características y protege al lomo de atún ante la pérdida de humedad y retrasa la degradación de las proteínas. De igual manera la carragenina mostró un mejor desempeño como empaque a concentraciones de 0,05% en comparación con la gelatina.Numerous studies have been focused to natural ingredients to maintain the quality and shell life of foods. Edibles coating, biodegradable ingredients, such as hydrocolloids and proteins can be used for coating fish with the purpose to suppress changes of quality during frozen storage. At the present time several developing of edibles packing, like glaze using hydrocolloids, (gelatin, carrageen, starch), that besides acts as protective film for food, they are economic, can be ingested by the consumer without toxicity risk, help to preserve organoleptics and nutritional characteristics of the product and, being biodegradable they contribute to the conservation of the atmosphere. The objective of the present study was to evaluate the incorporation of hydrocolloids in the glazing tuna process as alternative of packing, to enhance its physical and chemical characteristics. Samples of tuna was glazed incorporating to its solutions of carrageen at 0.05, 0,1 and 0.15%, and gelatin at 0.5, 1%. The samples were shaped as square (15 cm3), frozen al -30ºC and glazed incorporating hydrocolloids submerging the sample its solutions at 0 ºC by 30 seconds and storage at -10ºC by 0, 15 and 30 days. Proximal analysis results, soluble proteins, TBA, and color showed that all the samples glazed with hydrocolloids decrease deterioration of the tuna products respect to samples glazed without hydrocolloids; concluding that glazing adding hydrocolloids protects tuna for loss humidity and delays degradation of proteins. Moreover, carrageen shows to a better performance at the concentrations of 0.05% compared with the gelatin and the starch.

The main task of this paper is to describe digestive tract of bluefin tuna, with special focus on the liver. The samples for the research on tuna digestive tract where taken on the tuna farm »Sardina« d.d. Postira. The investigation were done on 22 samples (necropsy and photography of organs, Canon digital camera), 30 samples liver of unfatted tuna, 30 samples liver of fatted tuna and 20 histologic samples of liver before and after fattening. The quality of nutrition directly affects the differences of longitudinal and latitudinal values of the hepatosomatic index and the histology of liver of fatted and unfitted fish. Intensive, lipid–rich nutrition increases the quantity of the fat stored in liver therefore causing higher hepatosomatic index in fatted tuna. Histologic examination of fatted tuna indicates a beginning of hepatocytes degeneration with vacuolization of the cell and decentralized nuclei. Lack of eosinophilic granules in cytoplasm of hepatocytes indicates the cell’s inability of doing enzymatic activity, respectively its dysfunction.

The Mediterranean Sea is particularly endangered by microplastics (MPs), polymers, and additives. These contaminants can be ingested by fishes and, hence, translocate into tissues. We aimed to quantify MPs, polyethylene terephthalate (PET), polycarbonate (PC), bisphenol A (BPA), and p -phthalic acid (PTA) in the edible muscles of swordfish (Xiphias gladius) and bluefin tuna (Thunnus thynnus) caught in the Mediterranean Sea. The MPs were extracted from muscles and characterized by stereomicroscopy and Raman microspectroscopy, while the polymers (PET and PC) and additives (BPA and PTA) were identified by LC-MS/MS. The number of MPs ranged from 140 to 270 no. kg−1 in swordfish and from 160 to 270 no. kg−1 in tuna. The most frequent MP polymer was polypropylene in swordfish (33%) and in tuna (34.7%), while the most abundant pigments were PB115, PB116, PBr101/102. A similar level of plastic contamination was revealed in these two fish species with differences in shapes, colors, pigments and polymers of MPs. [Display omitted] • Microplastics were detected and characterized in the muscle of swordfish and tuna. • PET, PC, bisphenol A and p -phthalic acid were quantified by LC-MS/MS in fish muscle. • Plastic pigments were identified by RAMAN microspectroscopy. • Swordfish and tuna showed similar contamination by MPs, polymers and additives. • Different MP shapes, colors, pigments and polymers were observed in fishes. [ABSTRACT FROM AUTHOR]

• The biochemical content affects the Hg and Zn levels in bluefin tuna muscle tissue. • Lower Hg levels are associated with greater lipid and lower protein content. • Lower Zn levels are associated with lower lipid and greater protein content. • Mercury may pose a health risk to people regularly consuming bluefin tuna. • Consumers could reduce the risk of Hg by choosing high-fat bluefin tuna. This study determines the biochemical composition and metal concentrations (Hg, Fe, Zn, Cu) in muscle tissue of reared Atlantic bluefin tuna and investigates whether protein-lipid composition affects metal accumulation. A significant positive relationship was found between Hg concentrations and protein content, whereas a strong negative relationship between Hg concentrations and lipid content was revealed. Opposite results were obtained, correlating Zn concentrations with biochemical components. No correlations between the concentrations of the other two metals and the protein or lipid components were observed. Evidently, biochemical components may influence the accumulation of certain metals, but not in the same way. Although the analyzed tuna samples represent a rich source of essential metals, Hg may pose a risk to consumers. Our results suggest that a lower level of Hg can be associated with greater lipid and lower protein content. Consumers could reduce the health risk from Hg by choosing constantly high-fat bluefin tuna. [ABSTRACT FROM AUTHOR]

Chemical signatures in calcified structures of fishes represent natural tags of chemical and physical characteristics of the environment. The suitability of dorsal spines of Atlantic bluefin tuna ( Thunnus thynnus ) was investigated as an alternative non-invasive structure to otoliths. The spatial and temporal variability of trace elements was examined, for the first time, throughout the annual growth increments ( i.e. translucent and opaque bands) of Bluefin tuna spines from the Bay of Biscay. Four scanning-ablation line transects were drawn and examined using LA-ICPMS to test for differences in tracer concentrations for each spine sections. Firstly, results confirm the questionable spatial stability of tracers in dorsal fin spines. Secondly, most of the elements analyzed 88 Sr , 137 Ba , 24 Mg , 55 Mn , 7 Li (biological essential elements), 66 Zn and 65 Cu (priority pollutants) were consistenly found above the limit of detection (LOD). Strontium and Barium showed a similar pattern throughout annuli with concentrations significantly higher in the translucent bands in the second annulus ( i.e. second winter). The concentration of Magnesium displayed an increasing pattern with annulus with no differences between translucent and opaque bands. In contrast, the concentration of Manganese showed a decreasing pattern throughout annuli, with concentrations significantly higher in the opaque bands ( i.e. summer bands) regardless of annulus. Lithium, Copper and Zinc showed unclear pattern, although the concentration of Zinc seems to be in sync with the deposition of annuli currently interpreted in the ageing process. Findings indicate that the chemical signature of certain biologically essential elements is preserved stable in the dorsal fin spines strengthening its use as a non-invasive alternative structure for chemistry studies in Atlantic bluefin tuna. [ABSTRACT FROM AUTHOR]

Atlantic blue fin tuna (Thunnus thynnus) is a species of great importance for Mediterranean Sea area, from both ecological and commercial points of view. The scientific literature reports few data on the contamination of this fish by emerging organic compounds such as perfluorinated alkylated substances (PFASs) and phthalates, being the latter never been studied in tuna. This study therefore investigated the presence of the PFASs perfluorooctane sulphonate (PFOS) and perfluoroctanoic acid (PFOA) and the phthalate di-2-ethylhexyl phthalate (DEHP), also monitored by its metabolite mono-2-ethylhexyl phthalate (MEHP), to assess both the state of contamination of Atlantic bluefin tuna specimen and the risk due to the toxicity of these compounds for human consumption. While PFOA was never found, detectable levels of PFOS (0.4-1.88 ng/g), DEHP (9-14.62 ng/g) and MEHP (1.5-6.30 ng/g) were found. The results were elaborated relating the accumulation to the size and age of the individuals and showed a correlation between the levels of different pollutants investigated. [ABSTRACT FROM AUTHOR]

Persistent organic pollutants (POPs) are known to act as “obesogens”, being fat-soluble and affecting lipid metabolism. The Atlantic bluefin tuna, Thunnus thynnus , are top pelagic predators prone to bioaccumulate and biomagnify environmental contaminants. This study aimed at evaluating POPs-induced ectopic lipid accumulation in liver of adult tuna from the Mediterranean Sea. PCBs and organochlorine pesticides were measured in tuna liver, and marked morphological changes observed, namely poorly compacted tissues, intense vacuolization, erythrocyte infiltration and presence of melanomacrophages. The expression of perilipin, a lipid-droplet marker, positively correlated with the gene expression of PPARγ, a master regulator of adipogenesis, and its heterodimeric partner, RXRα. Changes in metabolites involved in fatty acid biosynthesis and ketogenesis were also observed. Although male bluefin tuna appeared to be more sensitive than females to the adverse effects of environmental obesogens, the alterations observed in tuna liver of both sexes suggest a potential onset of hepatic steatosis. [ABSTRACT FROM AUTHOR]

From late April until mid-June Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758), migrates along the western coast of Sardinia to reach spawning grounds of the Mediterranean. Despite the substantial information on the reproductive biology of the species, the tracking of its reproductive parameters along the migratory pathways is far to be completed. This study provides some reproductive parameters for adult bluefin tuna collected from the last trap fishery Tonnara of the Mediterranean. The following points summarize our results: (i) gonadosomatic index (GI) was positively correlated with fork length (FL) and varied significantly between sexes, having higher values in males; (ii) ovaries contained a mixture of oocyte stages with primary growth oocytes representing 72%, cortical alveoli 16%, primary and secondary vitellogenic stages 4.6% and 6% respectively, only a small proportion of late vitellogenic oocytes and atretic follicles; (iii) batch fecundity was 95–125 oocytes per gram of body mass and varied from 1.6 million for a female of 105 cm FL, to 29.5 million eggs for a 233 cm FL specimen; (iv) sex ratio differed significantly from 1:1, with males being predominant both for the size classes and years analyzed. These findings suggest that bluefin tuna from western Sardinia exhibits intermediate reproductive characteristics between specimens migrating through the Strait of Gibraltar and those from the spawning grounds of the Balearic Islands. [ABSTRACT FROM AUTHOR]

The fatty acid profile of crevalle jack was compared with that of Atlantic bluefin tuna, Atlantic Spanish mackerel, red snapper, and Nile tilapia. Crevalle jack and Atlantic Spanish mackerel showed similarities in their fatty acid profiles, with the saturated fatty acid > monounsaturated fatty acid > polyunsaturated fatty acid pattern. Atlantic bluefin tuna and red snapper followed a similar pattern to each other, with the polyunsaturated fatty acid > saturated fatty acid > monounsaturated fatty acid pattern, and the pattern for Nile tilapia was saturated fatty acid > monounsaturated fatty acid ≈ polyunsaturated fatty acid. In winter, the DHA+EPA content of crevalle jack (493.2 mg/100 g fillet) was 37% lower than Atlantic bluefin tuna and Atlantic Spanish mackerel, 35% higher than for the red snapper, and 2.8 fold higher than for the Nile tilapia. The best nutritional indices were for Atlantic bluefin tuna > red snapper > Atlantic Spanish mackerel > crevalle jack > Nile tilapia. [ABSTRACT FROM PUBLISHER]

The recently adopted model by ICCAT Standing Committee on Research and Statistics (SCRS) for the western Atlantic bluefin tuna (ABFT),Thunnus thynnus(L.)(RW= 0.0000159137SFL3.020584,WEST), together with the model used to date (RW= 0.0000152 SFL3.0531,Ec1) is analyzed in using a bi-variant sample (SFL(cm),RW(kg)) of 698 pairs of data (K= 2.02 ± 0.23 SD) in order to validate them and to establish the model that fits best the reality represented by the sample and, therefore, will have the greatest descriptive and predictive power. The result of the analysis indicates that the adopted modelWESTclearly underestimates the weight of spawning ABFT being modelEc1 that best explains the data of the sample. The result of the classical statistical analysis is confirmed by means of the quantile regression technique, selecting the quantiles 5%, 25%, 50%, 75%, and 95%. Other biological and fisheries indicators also conclude that the modelWESTgradually underestimates the weight of ABFT spawners (of 2–3 m) by 11–13%, does not meet the criterion that forRW= 725 kg (Wmax),SFL= 319.93 ± 11.3 cm (Lmax), and the average value ofK(1.77) obtained for a wide range of size–weight values, usingWESTmodel, represents ABFT in low fattening condition. [ABSTRACT FROM PUBLISHER]

In this study, we assessed the effect of environmental salinity and pH as independent factors on larval survival of Atlantic bluefin tuna (ABFT – Thunnus thynnus) together with their whole-body Na+/K+-ATPase and v-type H+-ATPase activities. Fertilized eggs of ABFT were obtained from a spontaneous spawning of broodstock in the farming facilities at El Gorguel (Cartagena, SE Spain) and were transferred to facilities of the Spanish Institute of Oceanography (IEO) in Mazarrón (SE Spain). In a first experiment, eggs (200 fertilized eggs L−1 per treatment, in 3 replicates) were exposed to different salinities treatments and constant pH 8.0 (control) until hatch was completed (50 h post-fertilization, hpf, at 23 °C): 27, 30, 33, 36, 37, 38 (control), 39, 40, 43, 46 and 49 ppt. In a second experiment eggs (200 fertilized eggs L−1, in 3 replicates) were exposed to seawater salinity (SW: 38 ppt) and four reduced pH treatments until hatch was completed (50 hpf at 23 °C): 8.0 (control), 7.7, 7.5 and 7.3. An inverse "U-shaped" relationship was observed between environmental salinity and number of hatched larvae. An opposite pattern was observed for both Na+/K+-ATPase and H+-ATPase activities in hatched larvae, increasing both activities in groups exposed to extreme salinities. Thus, larval survival was higher at intermediate salinities and lower at the extreme salinities tested. These results suggest higher survival rates with lower active pumps activities. No significant differences in larval survival were observed with pH treatment, but lower H+-ATPase activity was detected at control environmental pH (pH 8.0). Survival results are discussed in terms of osmoregulatory cost adapting to a salinity and pH predicted for the near future scenarios. • Atlantic bluefin tuna larvae survival is related to environmental salinity. • Higher larval survival rates are shown at 36–38 ppt. • Larval survival does not change within environmental pH from 8.0 to 7.3. • Larval survival is related to osmoregulatory processes. [ABSTRACT FROM AUTHOR]

A microscopic and a molecular approach was used to investigate blood fluke infection in the very first specimens of Atlantic bluefin tuna ( Thunnus thynnus , Scombridae) that were born in captivity and that were never moved from their specific cage culture sites in the Mediterranean. Data were compared with infection in wild, migratory bluefin tuna which were captured and fattened along the Spanish Mediterranean coast. Wild and cultured populations sampled in the present study harbored the same Cardicola spp. richness and showed statistically insignificant differences in overall parasite prevalence. Three morphotypes, crescent-shaped, fusiform and oval eggs, were observed in both non-migrant and migrant tuna. According to partial ITS2 and 28S rDNA sequences they belong to Cardicola opisthorchis , Cardicola forsteri , and to Cardicola sp., a recently described species, phylogenetically closely related to Cardicola orientalis . All three species were simultaneously present in some specimens. No significant difference in overall parasite prevalence was observed, though the prevalence of eggs of individual species, i.e. C. opisthorchis and C. forsteri , was significantly higher in fattened bluefin tuna. Our results strongly support a Mediterranean origin of the three Cardicola species encountered in cultured specimens and suggest that the intermediate hosts of these Cardicola species occur along the Mediterranean coast. Thus, infection with these parasites is not exclusively a result of infections happening along the migratory routes of wild bluefin tuna, in the Atlantic Ocean, as previously suggested. Once transferred to the sea for fattening, Atlantic bluefin tuna are at risk of infection with up to three different species of the genus Cardicola in along the Mediterranean coast in southeast Spain. On the contrary, C. orientalis infections might be associated to long-distance migration and an overlapping Thunnus maccoyii and Thunnus orientalis distribution. Statement of relevance This is the very first parasitological study conducted in T. thynnus born in captivity and cultured local in the Mediterranean. The results show that once transferred to the sea for fattening, they are at risk of infection with up to three different species of the genus Cardicola . These results strongly imply a Mediterranean distribution of these species. [ABSTRACT FROM AUTHOR]

Background: The largest of the tuna species, Atlantic bluefin tuna (Thunnus thynnus), inhabits the North Atlantic Ocean and the Mediterranean Sea and is considered to be an endangered species, largely a consequence of overfishing. T. thynnus aquaculture, referred to as fattening or farming, is a capture based activity dependent on yearly renewal from the wild. Thus, the development of aquaculture practices independent of wild resources can provide an important contribution towards ensuring security and sustainability of this species in the longer-term. The development of such practices is today greatly assisted by large scale transcriptomic studies. Results: We have used pyrosequencing technology to sequence a mixed-tissue normalised cDNA library, derived from adult T. thynnus. A total of 976,904 raw sequence reads were assembled into 33,105 unique transcripts having a mean length of 893 bases and an N50 of 870. Of these, 33.4 % showed similarity to known proteins or gene transcripts and 86.6 % of them were matched to the congeneric Pacific bluefin tuna (Thunnus orientalis) genome, compared to 70.3 % for the more distantly related Nile tilapia (Oreochromis niloticus) genome. Transcript sequences were used to develop a novel 15 K Agilent oligonucleotide DNA microarray for T. thynnus and comparative tissue gene expression profiles were inferred for gill, heart, liver, ovaries and testes. Functional contrasts were strongest between gills and ovaries. Gills were particularly associated with immune system, signal transduction and cell communication, while ovaries displayed signatures of glycan biosynthesis, nucleotide metabolism, transcription, translation, replication and repair. Conclusions: Sequence data generated from a novel mixed-tissue T. thynnus cDNA library provide an important transcriptomic resource that can be further employed for study of various aspects of T. thynnus ecology and genomics, with strong applications in aquaculture. Tissue-specific gene expression profiles inferred through the use of novel oligo-microarray can serve in the design of new and more focused transcriptomic studies for future research of tuna physiology and assessment of the welfare in a production environment. [ABSTRACT FROM AUTHOR]

Following an extensive description and review of the bibliography of the overall situation of the bluefin tuna,Thunnus thynnus(L.), ABFT, from ancient times until the present, the eastern Atlantic fisheries that traditionally caught ABFT spawners (traps of the Strait of Gibraltar and northern European fisheries) are described with the aim of explaining the reasons behind their decline from the 1960s. The study includes the fishery of the Bay of Biscay, an area where small and medium-sized spawners migrated towards areas of trophic concentration in the north of Europe. The fisheries of ABFT juveniles began to develop in the eastern Atlantic at the end of the 1940s (Bay of Biscay) and the middle of the 1950s (off the coast of Morocco). The results of an analysis of the juvenile ABFT population of the eastern Atlantic part between 1949 and 1962 reveal that under different scenarios the high fishing mortality exerted on the juvenile fish groups (<5 years) in the period studied may have been one of the main factors behind the decline of the north eastern Atlantic fisheries of spawners from 1963. Juvenile catches of that magnitude (6,879,967 ABFT) may have given rise to the limited recruitment from juvenile age to spawning stocks. The analysis has also been made for the periods 1970–2006 and the present (2009). In the first of these two cases, fishing mortality (F) fell as a result of a fall in the catch of juveniles, mainly the fishery of Morocco. Nevertheless, during these years, over 4 million specimens of 1 year were caught illegally in the Atlantic part of the eastern stock. The fall in F is now even greater due to the practically entire disappearance of the juvenile fisheries as a result of the implementation of the Pluriannual Recovery Plan (PRP) of theInternational Commission for the Conservation of Atlantic Tunas(ICCAT), which began in the fisheries of the eastern stock in 2007. [ABSTRACT FROM AUTHOR]

The growth of bluefin tuna ( Thunnus thynnus ) in the North-eastern Atlantic and Mediterranean was analysed using the back-calculation of the dorsal fin spine annuli. Spines from a total of 2678 bluefin tuna, collected from 1984 and 1990–2010, were analyzed. The specimens ranged from 45 to 287 cm straight fork length (SFL). Both linear and power regression functions showed a significant relationship between spine radius and SFL, but power function fitted better than linear (SFL = 42.978R 0.884 , r 2 = 0.98), as also was found in previous studies when a wide range of sizes was available. Two back-calculation equations were used to obtain the back-calculated SFL, Fraser-Lee and Body Proportional Hypothesis (BPH), showing similar results. The Von Bertalanffy growth parameters obtained with the selected BPH model were: SFL = 349.5(1 − e −0.086( t +0.814) ). Back-calculated lengths and growth parameters showed similarities with those from previous literature. [ABSTRACT FROM AUTHOR]

Mitochondrial DNA locus cytochrome oxidase I was used to asses intraspecific genetic diversity of a didymozoid species Didymosulcus katsuwonicola. Adult forms of this species live encapsulated in pairs in the gills of the reared Atlantic bluefin tuna (Thunnus thynnus). The life cycle of this food-borne parasites and its migration in the host tissues after releasing from the digestive tract to the definitive site in the gills are unknown. Our goal was to assess whether two encysted didymozoids share the same haplotype, indicative of a common maternal origin, as well as the extent of cross- in respect to self-fertilization strategy. Intraspecific comparison showed high haplotype diversity, while the presence of two matching haplotypes within a single cyst encompassed only 17% of sampled individuals. This infers that cross-fertilization between paired individuals within the cyst is more common mechanism than self-fertilization. Such hermaphroditic parasite's trait suggests the existence of intricate infection and reproduction mechanisms, presumably as an adaptation for successful fulfillment of their indirect life cycle through dissemination of genetically more diverse and consequently more fit offspring. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the current levels of heavy metals and trace elements in Atlantic bluefin tuna muscle tissues and how they are influenced by the fattening process and various life history parameters to ascertain whether the concentrations in muscle tissue exceed the maximum levels defined by the European Commission Decision and to evaluate the health risk posed by fish consumption. A total of 20 bluefin tuna reared in sea cages, ranging from 160 to 295 cm in length and from 80 to 540 kg in weight, were sampled from a bluefin tuna farm in the Ionian Sea. The condition factor K of each specimen was calculated and their age was estimated. Heavy metal and trace element (Hg, Zn, Fe and Cu) contents were determined in muscle tissue using cold vapour atomic absorption spectrometry and flame and graphite furnace atomic absorption spectrometry. The total Hg concentrations ranged from 0.28 to 1.28 mg kg–1 w/w, Zn from 5.81 to 76.37 mg kg–1 w/w, Fe from 12.14 to 39.58 mg kg–1 w/w, and Cu from 0.36 to 0.94 mg kg–1 w/w. Only 5% of the muscle samples of tuna contained Hg above the maximum level laid down by the European Commission Decision. Moreover, 15% of the muscle samples contained Zn above the maximum level, while Fe and Cu concentrations were within the acceptable tolerable guideline values. The reared bluefin tuna had lower concentrations of Hg than the wild ones from the Mediterranean Sea. Hg and Fe concentrations showed a positive relationship with size and age of bluefin tuna, whereas negative relationships were found for the concentrations of Zn and Cu. The estimated dietary intake values of the analysed metals were mostly below the derived guidelines. [ABSTRACT FROM PUBLISHER]

Fatty acid profiles were obtained from perigonadal fat of 98 adult Atlantic Bluefin tuna sampled from 2008 to 2010 at their confluence near the Gibraltar Strait as a consequence of their reproductive migration to the Mediterranean. Ten additional individuals caught, at the same season, off the Canary Islands, a place where no sexual migratory confluence occurred, were also sampled for their fatty acid signatures. Gender was not significant in explaining differences in fatty acids, and other biological traits such as weight, gonad index and fat/gonad ratio all together only accounted for 13.4% of total variation. Body weight was the more relevant factor and showed maximum positive correlation with 18:1n-9 and the 22:6n-3/20:5n-3 ratio (as carnivoy and higher trophic position markers), and maximum negative correlation with the flagellate marker fatty acid, 18:4n-3. Multivariate analysis of fatty acid trophic markers revealed a main source of data variation (66.9%) due to segregation of individuals in which part of the tuna population showed signatures characteristic of trophic resources from high latitude Atlantic ecosystems as revealed by elevated contents of the marker fatty acids, 20:1n-9 and 22:1n-11. The vast majority of tuna individuals were characterized by fatty acid profiles enriched in n-3 polyunsaturated fatty acids and more associated to temperate and subtropical Atlantic ecosystems in which haptophyte/dinophyte markers prevailed over those for diatoms at the base of their corresponding food webs. Fatty acid profiles of tuna from the Canary Islands were less dispersed than those caught at the Gibraltar Strait, reinforcing the assumption of the possible tuna confluence from different trophic grounds in this zone. [ABSTRACT FROM AUTHOR]

Following extensive review, a model of the Atlantic bluefin tuna (ABFT),Thunnus thynnus(L.), length–weight relationship for the eastern Atlantic and Mediterranean (RW= 0.0000188SFL3.01247;Ec 1) is presented on the basis of samples of ABFT spawners, with an average value of indexK= 2.03 ± 0.15SD, collected by the Atlantic traps of Portugal and Spain in the Strait of Gibraltar (1963; 1996–1998; 2000–2012), and a set of samples of juvenile fishes from ICCAT–GBYP (n= 707). The resulting model (Ec 1), together with the model used for the eastern stock assessment (RW= 0.000019607SFL3.0092;Ec 2) and a recently adopted by ICCAT Standing Committee on Research and Statistics (SCRS) (RW= 0.0000315551SFL2.898454;EAST) are analyzed in using a bi-variant sample [SFL(cm),RW(kg)] of 474 pairs of data with the aim of validating them and establishing which model(s) best fit the reality represented by the sample and, therefore, will have the greatest descriptive and predictive power. The result of the analysis indicates that the modelEASTclearly underestimates the weight of spawning ABFT and that modelEc 2overestimates it slightly, being modelEc 1that best explains the data of the sample. The result of the classical statistical analysis is confirmed by means of the quantile regression technique, selecting the quantiles 5, 25, 50, 75, and 95%. Other fisheries and biological indicators also conclude that the modelEASTgradually underestimates the weight of ABFT spawners (of 2–3 m) by 9–12.5 %, and does not meet the criterion that forRW= 725 kg (Wmax),SFL= 319.93 ± 11.3 cm (Lmax). [ABSTRACT FROM AUTHOR]