Factores de discriminación y tasas de renovación isotópica de nitrógeno en larvas de atún rojo de cultivo (Thunnus thynnus): efectos de la transferencia materna

The use of stable isotope analysis to study animal diets requires estimates of isotopic turnover rates (half time, t50) and discrimination factors (Δ) for an accurate interpretation of trophic patterns. The stable isotopes of carbon and nitrogen were analysed for eggs and reared larvae of Thunnus thynnus, as well as for the different diets supplied during the experiment. The results showed high values of δ15N in eggs and larvae (n=646) until 4 DAH. After this time lapse, the stable isotope values declined progressively until 12 DAH, when notochord flexion began. The δ13C showed an inverse trend, suggesting that maternal inheritance of the stable isotopes is evident until pre-flexion stages. This study proposes a model for estimating maternal isotopic signatures of bluefin broodstock. After notochord flexion, larvae were fed with aquaculture-bred gilthead seabream, which resulted in a rapid increase of bluefin larvae δ15N values together with a rapid decrease in δ13C values. The estimated nitrogen half-time to reach the steady state from the diet was 2.5±0.3 days and the discrimination factor was 0.4±0.3(‰). These results represent the first data set that has allowed isotopic nitrogen turnover rates and discrimination factors of the larval stages of bluefin tuna to be estimated.El análisis de isótopos estables para estudiar la dieta de los animales requiere estimaciones de las tasas de rotación isotópicas (tiempo medio, t50) y factores de discriminación (Δ) para una correcta interpretación de los patrones tróficos. Los isótopos estables de carbono y nitrógeno se analizaron en los huevos y larvas criadas de Thunnus thynnus, así como para las diferentes dietas suministradas durante el experimento. Los resultados mostraron altos valores de δ15N en huevos y larvas (n=646) hasta cuatro días después de eclosionar. Después de este lapso de tiempo, los valores de los isótopos estables disminuyeron progresivamente hasta el día 12, cuando se inició la flexión de la notocorda. El δ13C mostró una tendencia inversa, lo que sugiere que la herencia materna de los isótopos estables es evidente en la etapa de pre-flexión. Este estudio propone un modelo para estimar las firmas isotópicas maternas de reproductores de atún rojo. Después de la flexión de la notocorda, las larvas se alimentaron con larvas recién eclosionadas de dorada, lo que dio lugar a un rápido aumento de los valores de δ15N en las larvas de atún rojo, junto con una rápida disminución del δ13C. El tiempo medio de nitrógeno para alcanzar el equilibrio con la dieta fue de 2,5±0,3 días y el factor de discriminación fue de 0,4±0,3(‰). Estos resultados representan el primer conjunto de datos que permitió la estimación de la tasa de renovación isotópica de nitrógeno y de los factores de discriminación en los estadios larvales de atún rojo

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

Arginine Vasotocin and Cortisol Co-regulate Vasotocinergic, Isotocinergic, Stress, and Thyroid Pathways in the Gilthead Sea Bream (Sparus aurata)

In teleosts, a complex interaction between several endocrine axes modulates physiological functions related to metabolism, stress, and osmoregulation. Although many studies in fish underline the interconnection between the hypothalamic– pituitary–interrenal (HPI) and hypothalamic–pituitary–thyroid (HPT) endocrine axes, their relationship with the vasotocinergic and isotocinergic systems remains unknown. The aim of the present study is therefore to shed light on the potential cross-regulations between HPT, HPI, and the vasotocinergic and isotocinergic axes in gilthead sea bream (Sparus aurata) at hypothalamic, hypophyseal, and plasma levels. Sea breams were administered with intraperitoneal slow-release implants containing different doses of vasotocin (the active peptide in vasotocinergic system) or cortisol (the last component of HPI axis). Plasma osmolality was higher in active neuropeptides vasotocin (Avt)- treated fish, indicating an osmoregulatory function of this hormone. Low concentrations of Avt increased hypothalamic arginine vasotocin precursor (avt) mRNA levels and increased Avt storage in the pituitary. Avt treatment down-regulated hypothalamic arginine vasotocin receptor v1a-type (avtrv1a), suggesting a negative paracrine coregulation of the HPI axis due to the close location of avtrv1a and adrenocorticotropin hormone (Acth) cells in the anterior pituitary. Furthermore, the up-regulation observed in arginine vasotocin receptor v2-type (avtrv2) suggests their involvement in metabolic and cortisol-related pathways in the hypothalamus. The decrease in isotocin (It) pituitary storage and the up-regulation of it receptor, observed in the Avt-treated group, reinforce the idea of an interconnection between the vasotocinergic and isotocinergic systems. Cortisol and Avt administration each inhibited the HPI axis, down-regulating crh gene expression in the absence of variations in corticotropin releasing hormone binding protein (crhbp). Finally, both hormonal treatments activated the HPT axis via upregulation of trh and down-regulation of thrb. Our results provide evidence for strong interactions among the Avt/It, HPI, and HPT axes of marine teleosts, particularly at the hypothalamic level

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