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Egg specific gravity is of relevance for fish recruitment since the ability to float influences egg and larvae development, dispersal and connectivity between fishing grounds. Using zootechnics, histological approaches, optical and electronic transmission microscopy, this study describes the morphogenetic mechanism of adhesion of the oil-drop covering layer (OCL) to the oil droplet (OD) in embryos of Merluccius merluccius under physical conditions reflecting the marine environment. The herein described primordial (p)OCL is a substructure of the inner yolk syncytial layer which contains egg organella aimed to mobilize lipidic reserves from the oil drop (OD) towards the embryo blood. It is shown that the timely OD-OCL assembly is a critical morphogenetic process for embryo and larvae survival. Such assembly depends on egg buoyance because of its influence on the embryo capacity to rotate within the perivitelline space. Therefore, oil droplet adhesion (ODA) eggs are capable to complete their development while oil droplet non-adhesion eggs (ODNA) dye soon after hatching. We show that gravity-dependent egg buoyance categories exhibit different ODA/ODNA ratios (0–77%) and that relationship diminishes under incubation systems such as sprayers, that do not assure a dynamic seawater surface mixing to avoid egg desiccation. As an adaptive trait, egg gravity strongly depends on oceanic properties such as current dynamics, turbulence, oxygen, rainfall, and salinity, whose rapid changes would likely challenge the sustainability of fisheries recruitment. [ABSTRACT FROM AUTHOR]

Food imprinting has both ecological and evolutionary significance but the generality of these patterns for octopods remains unknown. We aim to determine the prey preference of Octopus berrima hatchlings and whether it may be modified through imprinting. Firstly, hatchlings were given isopods, amphipods and mussels to determine their prey preference ranking. In a separate experiment, embryos were exposed to the visual and chemical stimuli of either isopods, amphipods or mussels separately at least a week before hatching. A prey preference test on hatchlings using all three prey types was conducted. We found that O. berrima had a preference ranking of isopods > amphipods > mussels. However, they retained their isopod prey preference regardless of the prey type they were embryonically exposed to, indicating that it is likely pre-determined as a result of innate biological processes rather than from life experience, providing evidence that imprinting does not occur in O. berrima. [ABSTRACT FROM AUTHOR]

Diversification of marine species has emerged as a priority in the aquaculture agenda of many countries due to its large industrial potential and as an alternative to overharvested fisheries. Aquaculture diversification entails new challenges during early life stages of candidate species such as survival bottlenecks or body malformations, many of them due to uncoupling between classic diets and early nutritional requirements. Monospecific diets are common in fish aquaculture, e.g. beginning with a rotifer-based diet, followed by a mixed diet of rotifer and artemia nauplii and ending with artemia nauplii and metanauplii until weaning. Despite some success was reported using such protocol in early hake feeding the massive mortality observed as approaching 25 dph makes optimization of early feeding and larval management a current challenge for the domestication of this species. The main goal of this study was to design and test a workflow management system for early feeding of the European hake as a candidate species. The null hypothesis tested was that optimization of rearing settings had no effect on early growth and survival up to 30 dph as compared to classic culture protocols using commercial prey. Absence of prey in 6 dph hake larvae stomachs indicates that their external feeding at 14 °C begins just after that age. Early feeding preference depends on prey size (< 500 μm before 9 dph) as well as on pigmentation and behavior e.g. those with poor escape reactivity such as A. franciscana Nauplii. Significant feeding specialization on wild zooplankton such as P. intermedius and T. longicornis occurred after 9 dph (Chesson selectivity index = 0.11). Feeding activity was maximal in darkness (D) and medium light intensity (600 lx, MLI) as compared to the lethal light intensity of 1700 lx (HLI). Rotifer-based diets entailed low larvae growth and hake culture unviability after 15 dph but inclusion of wild zooplankton in early diets doubled growth of 30 dph larvae regarding artemia-based diets. The adaptive prey-size diet designed (MiACop) by combining stages of copepods (nauplii, copepodite and adult), rotifer and commercial nauplii of artemia was five-fold superior to the artemia/zooplankton diet all along the first 30 dph larvae culture. The massive cannibalism observed from 25 dph on was related to the absence of an adequate prey size such as that of mysids and euphausiids in combination with semi-dry feed to trigger weaning. Current workflow design for early feeding of the European hake can be helpful to assuring a larger proportion of juveniles entering the weaning phase. Statement of relevance First feeding of the European hake. [ABSTRACT FROM AUTHOR]

This study describes the effect of seasonal average temperatures (14 and 18°C) in the Ría of Vigo, on the utilization of external yolk over the last five Naef stages of development ( XV- XX) for Octopus vulgaris embryos. Also, the transference of the outer yolk to the inner yolk sac, and its use during embryonic development and early life by O. vulgaris paralarvae. Temperature had a marked effect on embryonic development, except during stages XV- XIX (until the second inversion) where development time was the same (14 days), regardless of temperature. There were no significant differences in outer yolk decrease between consecutive Naef stages at 14°C and 18°C. Contrary, significant differences at all Naef stages from XV to XIX (both, with or without outer yolk) were observed for inner yolk between temperatures. A higher accumulation of inner yolk in embryos at 14°C was observed, due to lower yolk consumption. Paralarvae incubated at both temperatures were maintained independently at starvation during 4 days. At 18°C, a reduced accumulation of inner yolk, especially during Naef stage XIX, was observed. In 24 h old paralarvae, there was already significant higher inner yolk content at 14°C than at 18°C. Unfed paralarvae at 18°C lost weight faster than those at 14°C, due to higher energetic requirements. Finally, from these results, we propose a paralarvae rearing protocol during the first days after hatching and during the last five Naef stage ( XV- XX) at lower temperatures, since the energy requirements are lower during the initial maturation stage. [ABSTRACT FROM AUTHOR]

The European sardine (Sardina pilchardus, Walbaum 1792) is indisputably a commercially important species. Previous studies using uneven sampling or a limited number of makers have presented sometimes conflicting evidence of the genetic structure of S. pilchardus populations. Here, we show that whole genome data from 108 individuals from 16 sampling areas across 5000 km of the species' distribution range (from the Eastern Mediterranean to the archipelago of Azores) support at least three genetic clusters. One includes individuals from Azores and Madeira, with evidence of substructure separating these two archipelagos in the Atlantic. Another cluster broadly corresponds to the center of the distribution, including the sampling sites around Iberia, separated by the Almeria–Oran front from the third cluster that includes all of the Mediterranean samples, except those from the Alboran Sea. Individuals from the Canary Islands appear to belong to the Mediterranean cluster. This suggests at least two important geographical barriers to gene flow, even though these do not seem complete, with many individuals from around Iberia and the Mediterranean showing some patterns compatible with admixture with other genetic clusters. Genomic regions corresponding to the top outliers of genetic differentiation are located in areas of low recombination indicative that genetic architecture also has a role in shaping population structure. These regions include genes related to otolith formation, a calcium carbonate structure in the inner ear previously used to distinguish S. pilchardus populations. Our results provide a baseline for further characterization of physical and genetic barriers that divide European sardine populations, and information for transnational stock management of this highly exploited species towards sustainable fisheries. [ABSTRACT FROM AUTHOR]

This study analyzes the effect of low salinity on survival and daily food ingestion of octopus subjected to three different water salinities (20, 25, and 30 psu) for 3 days. During the 3-day experiment, octopuses at 20 psu immediately stopped eating, and all died during the first day; at 25 and 30 psu, the octopuses gradually reduced their feed intake and stopped eating after 2 days, but all survived, and when normal salinity conditions were reestablished (34–35 psu), they ingested 30–40 (~27.5% of the initial food intake) and 70–90 g of food/day (~63% of the initial food intake) respectively over the 5-day recovery period. Water salinity of 30 psu could be considered as the recommended lower limit below which actions, such as transferring the commercial floating cages to another location or submerging them, should be taken in order to prevent the negative effects of low salinities on farmed octopuses. [ABSTRACT FROM PUBLISHER]