Plasticidad del crecimiento larvario entre atún rojo y melva modulado por sus interacciones tróficas.

ECOlogía trófica comparativa de LArvas de aTUN rojo atlántico (Thunnus thynnus) de las áreas de puesta del Medterraneo-NO y el Golfo de México.ECOLATU

Impact of an immunostimulant diet and constant temperature on liver carbohydrate metabolism in the gilthead seabream Sparus aurata Linnaeus, 1758

The impact of an immunostimulant diet -frequently used to avoid winter syndrome in aquaculture- on liver carbohydrate metabolism was assessed over a period of 230 days in the gilthead sea bream Sparus aurata L., 1758. An enhancement of liver glycolytic, glycogenolytic and gluconeogenic potential in fish fed with immunostimulant diet was found, compared to a control group, suggesting an increase in liver metabolic activity. Moreover, immunostimulant-treated fish also showed higher values of lysozyme activity, along with a decrease in mortality, suggesting an increase in the nonspecific defence mechanism. The group kept at a 20°C constant temperature maintained appetite at normal levels, avoiding possible winter syndrome and obtaining better values for the production parameters studied (final weight, weight gain and mortality), compared with the control group.Se ha estudiado el efecto de una dieta inmunoestimuladora, usada frecuentemente en acuicultura para mitigar los efectos de la denominada enfermedad de invierno, y del mantenimiento a temperatura constante sobre el metabolismo hepático, los niveles de lisozimas y la mortalidad en dorada Sparus aurata L., 1758. El experimento se desarrolló durante un periodo de 230 días, observándose un incremento en los potenciales glucolítico y glucogenolítico, así como en el potencial gluconeogénico en el hígado de los ejemplares alimentados con la dieta inmunoestimuladora en relación al grupo de control. Estos resultados sugieren un aumento de la actividad metabólica hepática derivada de la dieta inmunoestimuladora. Asimismo, se observaron valores más elevados de los niveles de lisozimas simultáneos a una reducción de la mortalidad en el grupo tratado con inmunoestimuladores, lo que induce a concluir que esta dieta enriquecida fortalecería los mecanismos defensivos inespecíficos, disminuyendo la mortalidad. En el grupo de permanencia a temperatura constante de 20ºC se consiguió mantener el apetito de los peces y, por tanto, favorecer la prevención del posible síndrome de invierno, obteniéndose mejores valores en las distintas variables de producción estudiadas (peso final, ganancia de peso y mortalidad) con respecto al grupo de control.Instituto Español de OceanografíaVersión de editor

Biophysical Processes Determining the Connectivity of the Alboran Sea Fish Populations

This chapter revises biogeophysical issues of connectivity processes for fish populations in the Alboran Sea—Strait of Gibraltar—Gulf of Cadiz area. Connectivity of early life history stages between distant spawning grounds is crucial to incorporate vital developmental rates that condition survival probabilities at critical ontogenic stages. Hydrodynamics is pivotal to the process and most particular for pelagic species originating from adult fish adapted to recurrent patterns. Therefore, special focus has been placed on the hydrodynamics of the region, particularly on the Alboran Sea where the swift and energetic eastward-flowing Atlantic Jet entering the basin from the Strait of Gibraltar determines the surface circulation patterns. The Jet establishes an obvious zonal west-to-east connectivity, prevents the one in the opposite east-to-west direction and works as a hydrodynamic barrier that hampers the north-to-south connectivity. The chapter addresses these processes, discusses possible mechanisms to achieve connectivity between north and south shores, which have to overcome the hydrodynamic barrier, and assesses the feasibility of east-to-west connectivity by means of intermediate-depth currents. Implications on the populations and ecosystems of the Alboran Sea and on the three main harvested species potentially affected by hydrodynamic connectivity in the basin (European hake, the sardine, and the blackspot seabream) are also commented.Preprin

Maternal transference of isotopic signature (δ15N, δ13C) and Its evolution during ontogenic development of reared bluefin larvae (Thunnus thynnus)

An experimental rearing experiment of bluefin tuna larvae was undertaken in the Spanish Oceanographic Institution (IEO) based in the aquaculture plant of Murcia that started June 24, 2013 when caged bluefin spawned naturally. Bluefin tuna eggs were transferred to rearing tanks and where hatched larvae were sampled regularly every 2 days till 15dph. After this period, larvae were sampled every 3 days till 37dph (Temperature range 22-26ºC). The standard length (SL) of larvae were measured after frozen and conserved deep-frozen in a -80ºC for undertaking posterior nitrogen (N) and carbon (C) stable isotope analysis. The results of the experiment showed very high initial values of δ15N and δ13C in the eggs and lecitotrophic larvae till 4dph, explaining a transgenerational transference of the heavy isotopes through maternal inheritance. After this time lapse, the stable isotope values declined progressively till 12dph and maintained this low level till 15dph. This period coincides with the notochord post-flexion development established at a mean SL of 6,7mm (±0,57) measured. Coinciding with this ontogenic stage, larvae were started to be fed with newly hatched larvae of aquaculture-bred gilt-head seabream whose δ15N and δ13C values were consequently enriched. This diet produced an increasing trend in the δ15N and δ13C values till 24dph reaching similar values of the initial developmental times. The results show that pre-flexion larvae of bluefin have high δ15N and δ13C signature as a result of their maternal transference. A similar decreasing pattern was also observed in field-based research on bluefin larvae which justified the need to carry out this rearing experiment. The data acquired in this experiment allows to formulate an estimate of the maternal δ15N and δ13C signatures from larvae between 3-6mm SL which opens research horizons in the estimation of maternal trophic qualities that may relate to larval growth and condition potentials. This work was financed by the project ATAME CTM2011-29525-C04-02

Survival of Atlantic bluefin tuna (Thunnus thynnus) larvae hatched at different salinity and pH conditions

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 ºC): 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 ºC): 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.Versión del edito

Influence of food quality on larval growth of Atlantic bluefin tuna (Thunnus thynnus) in the Gulf of Mexico

Larval abundances of Atlantic bluefin tuna (ABT) in the Gulf of Mexico are currently utilized to inform future recruitment by providing a proxy for the spawning potential of western ABT stock. Inclusion of interannual variations in larval growth is a key advance needed to translate larval abundance to recruitment success. However, little is known about the drivers of growth variations during the first weeks of life. We sampled patches of western ABT larvae in 3–4 day Lagrangian experiments in May 2017 and 2018, and assessed age and growth rates from sagittal otoliths relative to size categories of zooplankton biomass and larval feeding behaviors from stomach contents. Growth rates were similar, on average, between patches (0.37 versus 0.39 mm d−1) but differed significantly through ontogeny and were correlated with a food limitation index, highlighting the importance of prey availability. Otolith increment widths were larger for postflexion stages in 2018, coincident with high feeding on preferred prey (mainly cladocerans) and presumably higher biomass of more favorable prey type. Faster growth reflected in the otolith microstructures may improve survival during the highly vulnerable larval stages of ABT, with direct implications for recruitment processes.En prensa1,74

SURVIVAL OF ATLANTIC BLUEFIN TUNA (THUNNUS THYNNUS) LARVAE HATCHED AT DIFFERENT PH AND SALINITY CONDITIONS

In this study, we assessed the effect of pH and salinity as independent factors on larval survival (LS) of Atlantic bluefin tuna (ABFT –Thunnus thynnus) together with their Na+/K+-ATPase and V-type H+-ATPase activities. Fertilized eggs of ABFT were obtained on 25 June 2016 from a spontaneous spawning of broodstock in the farming facilities at El Gorguel (Cartagena, SE Spain) of Caladeros del Mediterráneo Company. The fertilized eggs were transferred to facilities of the Spanish Institute of Oceanography (IEO) in Mazarrón (SE Spain). In a first experiment, eggs (n = 150 per treatment, in 3 replicates) were exposed to sea water salinity (SW: 38 ppt) and four pH treatments until hatch was completed (44 hours at 23 ºC): 8.0 (control), 7.7 (near future), 7.5 (far future) and 7.3 (lower). In a second experiment eggs (n = 150 per treatment, in 3 replicates) were exposed to eleven salinities treatments and constant pH 8.0 (control) until hatch was completed (44 hours at 23 ºC): 27 , 30 , 33 , 36 , 37 , 38 (control), 39 , 40 , 43 , 46 and 49 ppt. No significant differences in LS were observed with pH treatment, but lower H+-ATPase activity was detected at control environmental pH (pH 8.0). A ‘‘U-shaped’’ relationship was observed between hatching salinity and both Na+/K+-ATPase and H+-ATPase activities in whole larvae hatched, increasing both activities in groups exposed to extreme salinities. However, LS showed an inverse “U shape” curve respect to environmental salinity with higher values at intermediate salinities and lower LS at extreme salinities. These results suggest higher survival rates with lower active pumps activities. Survival results are discussed in terms of osmoregulatory cost adapting to a pH and salinity predicted for the near future scenarios. This work was funding by the European Union’s Horizon 2020research and innovation programme under Grant Agreement No. 678193

Bluefin Tuna Larvae in Oligotrophic Ocean Foodwebs, Investigations of Nutrients to Zooplankton: Overview of the BLOOFINZ-Gulf of Mexico program

Western Atlantic bluefin tuna (ABT) undertake long-distance migrations from rich feeding grounds in the North Atlantic to spawn in oligotrophic waters of the Gulf of Mexico (GoM). Stock recruitment is strongly affected by interannual variability in the physical features associated with ABT larvae, but the nutrient sources and food-web structure of preferred habitat, the edges of anticyclonic loop eddies, are unknown. Here, we describe the goals, physical context, design and major findings of an end-to-end process study conducted during peak ABT spawning in May 2017 and 2018. Mesoscale features in the oceanic GoM were surveyed for larvae, and five multi-day Lagrangian experiments measured hydrography and nutrients; plankton biomass and composition from bacteria to zooplankton and fish larvae; phytoplankton nutrient uptake, productivity and taxon-specific growth rates; micro- and mesozooplankton grazing; particle export; and ABT larval feeding and growth rates. We provide a general introduction to the BLOOFINZ-GoM project (Bluefin tuna Larvae in Oligotrophic Ocean Foodwebs, Investigation of Nitrogen to Zooplankton) and highlight the finding, based on backtracking of experimental waters to their positions weeks earlier, that lateral transport from the continental slope region may be more of a key determinant of available habitat utilized by larvae than eddy edges per se.Postprint1,74