Effect of dietary l-glutamine supplementation on the intestinal physiology and growth during Solea senegalensis larval development.

The maturation of the intestinal digestive and absorptive functions might limit the amount of absorbed nutrients to fulfil the high requirements of the fast-growing marine fish larva. Glutamine (Gln) has been described to improve intestinal epithelium functions, due to its involvement in energy metabolism and protein synthesis. The purpose of this study was to evaluate dietary 0.2% Gln supplementation on aspects of intestinal physiology, protein metabolism and growth-related genes expression in Senegalese sole larvae. Experiment was carried out between 12 and 33 days post hatching (DPH) and fish were divided into two experimental groups, one fed Artemia spp. (CTRL) and the other fed Artemia spp. supplemented with Gln (GLN). GLN diet had two times more Gln than the CTRL diet. Samples were collected at 15, 19, 26 and 33 DPH for biometry, histology, and digestive enzymes activity, and at 33 DPH for gene expression, protein metabolism and AA content determination. Growth was significantly higher for Senegalese sole fed GLN diet, supported by differences on protein metabolism and growth-related gene expression. Slight differences were observed between treatments regarding the intestinal physiology. Overall, GLN diet seems to be directed to enhance protein metabolism leading to higher larval growth.

Early life stage mechanisms of an active fish species to cope with ocean warming and hypoxia as interacting stressors.

Ocean's characteristics are rapidly changing, modifying environmental suitability for early life stages of fish. We assessed whether the chronic effects of warming (24 °C) and hypoxia (<2-2.5 mg L-1) will be amplified by the combination of these stressors on mortality, growth, behaviour, metabolism and oxidative stress of early stages of the white seabream Diplodus sargus. Combined warming and hypoxia synergistically increased larval mortality by >51%. Warming induced faster growth in length and slower gains in weight when compared to other treatments. Boldness and exploration were not directly affected, but swimming activity increased under all test treatments. Under the combination of warming and hypoxia, routine metabolic rate (RMR) significantly decreases when compared to other treatments and shows a negative thermal dependence. Superoxide dismutase and catalase activities increased under warming and were maintained similar to control levels under hypoxia or under combined stressors. Under hypoxia, the enzymatic activities were not enough to prevent oxidative damages as lipid peroxidation and DNA damage increased above control levels. Hypoxia reduced electron transport system activity (cellular respiration) and isocitrate dehydrogenase activity (aerobic metabolism) below control levels. However, lactate dehydrogenase activity (anaerobic metabolism) did not differ among treatments. A Redundancy Analysis showed that ∼99% of the variability in mortality, growth, behaviour and RMR among treatments can be explained by molecular responses. Mortality and growth are highly influenced by oxidative stress and energy metabolism, exhibiting a positive relationship with reactive oxygen species and a negative relationship with aerobic metabolism, regardless of treatment. Under hypoxic condition, RMR, boldness and swimming activity have a positive relationship with anaerobic metabolism regardless of temperature. Thus, seabreams may use anaerobic reliance to counterbalance the effects of the stressors on RMR, activity and growth. The outcomes suggests that early life stages of white seabream overcame the single and combined effects of hypoxia and warming.

Lack of detrimental effects of ocean acidification and warming on proximate composition, fitness and energy budget of juvenile Senegalese sole (Solea senegalensis).

Rising levels of atmospheric carbon dioxide (CO2) are driving ocean warming and acidification, which may negatively affect the nutritional quality and physiological performance of commercially important fish species. Thus, this study aimed to evaluate the effects of ocean acidification (OA; ΔpH = -0.3 units equivalent to ΔpCO2 ~ +600 µatm) and warming (OW; ΔT = +4 °C) (and combined, OAW) on the proximate composition, fitness and energy budget of juvenile Senegalese sole (Solea senegalensis). After an exposure period of 75 days, growth (G), metabolism (R) and excretion (faecal, F and nitrogenous losses, U) were assessed to calculate the energy intake (C). Biometric and viscera weight data were also registered to determine animal fitness. Overall, the proximate composition and gross energy were not significantly affected by acidification and warming (alone or in combination). Weight gain, maximum and standard metabolic rates (MMR and SMR, respectively), aerobic scope (AS) and C were significantly higher in fish subjected to OA, OW and OAW than in CTR conditions. Furthermore, the highest relative growth rates (RGR), specific growth rates in terms of wet weight (SGRw) and protein (SGRp), as well as feed efficiencies (FE) occurred in fish submitted to OW and OAW. On the other hand, fish exposed to CTR conditions had significantly higher feed conversion ratio (FCR) and ammonia excretion rate (AER) than those exposed to simulated stressors. Regarding energy distribution, the highest fraction was generally allocated to growth (48-63 %), followed by excretion through faeces (36-51 %), respiration (approximately 1 %) and ammonia excretion (0.1-0.2 %) in all treatments. Therefore, ocean warming and acidification can trigger physiological responses in juvenile Senegalese sole, particularly in their energy budget, which can affect the energy flow and allocation of its population. However, and in general, this species seems highly resilient to these predicted ocean climate change stressors.

Effects of exposure to elevated temperature and different food levels on the escape response and metabolism of early life stages of white seabream, Diplodus sargus.

Recent literature suggests that anthropogenic stressors can disrupt ecologically relevant behaviours in fish, such as the ability to escape from predators. Disruption of these behaviours at critical life history transitions, such as the transition from the pelagic environment to the juvenile/adult habitat, may have even greater repercussions. The literature suggests that an increase in temperature can affect fish escape response, as well as metabolism; however, few studies have focused on the acute sensitivity responses and the potential for acclimation through developmental plasticity. Here, we aimed at evaluating the acute and long-term effects of exposure to warming conditions on the escape response and routine metabolic rate (RMR) of early life stages of the white seabream, Diplodus sargus. Additionally, as food availability may modulate the response to warming, we further tested the effects of long-term exposure to high temperature and food shortage, as individual and interacting drivers, on escape response and RMR. Temperature treatments were adjusted to ambient temperature (19°C) and a high temperature (22°C). Feeding treatments were established as high ration and low ration (50% of high ration). Escape response and RMR were measured after the high temperature was reached (acute exposure) and after 4 weeks (prolonged exposure). Acute warming had a significant effect on escape response and generated an upward trend in RMR. In the long term, however, there seems to be an acclimation of the escape response and RMR. Food shortage, interacting with high temperature, led to an increase in latency response and a significant reduction in RMR. The current study provides relevant experimental data on fishes' behavioural and physiological responses to the combined effects of multiple stressors. This knowledge can be incorporated in recruitment models, thereby contributing to fine-tuning of models required for fisheries management and species conservation.

Can the toxicity of polyethylene microplastics and engineered nanoclays on flatfish (Solea senegalensis) be influenced by the presence of each other?

Microplastics and nanomaterials are applied in a myriad of commercial and industrial applications. When leaked to natural environments, such small particles might threaten living organisms' health, particularly when considering their potential combination that remains poorly investigated. This study investigated the physiological and biochemical effects of polyethylene (PE; 64-125 µm in size, 0.1, 1.0, and 10.0 mg·L-1) single and combined with an engineered nanomaterial applied in antifouling coatings, the copper-aluminium layered double hydroxides (Cu-Al LDH; 0.33, 1.0, and 3.33 mg·L-1) in the flatfish Solea senegalensis larvae (8 dph) after 3 h exposure, in a full factorial design. Particles ingestion, histopathology, and biochemical biomarkers were assessed. Fish larvae presented <1 PE particles in their gut, independently of their concentration in the medium. The histological health index showed minimal pathological alterations at PE combined exposure, with a higher value observed at 1 mg LDH·L-1 × 0.1 mg PE·L-1. Gut deformity and increased antioxidant defences (catalase), neurotransmission (acetylcholinesterase), and aerobic energy production (electron transport system) were observed at PE ≥ 1.0 mg·L-1. No oxidative damage (lipid peroxidation) or alterations in the detoxification capacity (glutathione-S-transferase) was observed on single and combined exposures. PE, combined or not with Cu-Al LDH, does not seem to compromise larvae's homeostasis considering levels reported so far in the marine and aquaculture environments. However, harsh effects are expected with MP contamination rise, as projections suggest.

Draft Genome Sequence of Vibrio jasicida 20LP, an Opportunistic Bacterium Isolated from Fish Larvae.

We present the genome sequence of Vibrio jasicida 20LP, a bacterial strain retrieved from larvae of gilthead seabream (Sparus aurata), a highly valuable, model fish species in land-based aquaculture. Annotation of the V. jasicida 20LP genome reveals multiple genomic features potentially underpinning opportunistic associations with diverse marine animals.

Draft Genome Sequence of Vibrio chagasii 18LP, Isolated from Gilthead Seabream (Sparus aurata) Larvae Reared in Aquaculture.

We report the draft genome sequence of Vibrio chagasii strain 18LP, isolated from gilthead seabream larvae at a fish hatchery research station in Portugal. The genome presents numerous features underlying opportunistic behavior, including genes coding for toxin biosynthesis and tolerance, host cell invasion, and heavy metal resistance.

Molecular Taxonomic Profiling of Bacterial Communities in a Gilthead Seabream (Sparus aurata) Hatchery.

As wild fish stocks decline worldwide, land-based fish rearing is likely to be of increasing relevance to feeding future human generations. Little is known about the structure and role of microbial communities in fish aquaculture, particularly at larval developmental stages where the fish microbiome develops and host animals are most susceptible to disease. We employed next-generation sequencing (NGS) of 16S rRNA gene reads amplified from total community DNA to reveal the structure of bacterial communities in a gilthead seabream (Sparus aurata) larviculture system. Early- (2 days after hatching) and late-stage (34 days after hatching) fish larvae presented remarkably divergent bacterial consortia, with the genera Pseudoalteromonas, Marinomonas, Acinetobacter, and Acidocella (besides several unclassified Alphaproteobacteria) dominating the former, and Actinobacillus, Streptococcus, Massilia, Paracoccus, and Pseudomonas being prevalent in the latter. A significant reduction in rearing-water bacterial diversity was observed during the larviculture trial, characterized by higher abundance of the Cryomorphaceae family (Bacteroidetes), known to populate microniches with high organic load, in late-stage rearing water in comparison with early-stage rearing-water. Furthermore, we observed the recruitment, into host tissues, of several bacterial phylotypes-including putative pathogens as well as mutualists-that were detected at negligible densities in rearing-water or in the live feed (i.e., rotifers and artemia). These results suggest that, besides host-driven selective forces, both the live feed and the surrounding rearing environment contribute to shaping the microbiome of farmed gilthead sea-bream larvae, and that a differential establishment of host-associated bacteria takes place during larval development.

Comparative analysis on natural spawning of F1 meagre, Argyrosomus regius, with wild broodstock spawns in Portugal.

The purpose of this study was to describe and compare the reproductive success and egg and larvae quality between wild and first-generation (F1) breeders of Argyrosomus regius. Wild broodstock were adapted to captivity, and good-quality spawns were obtained in 2009-2010, after GnRH treatment. In 2012, the F1 meagre (3 years old) spawned naturally at IPMA's Aquaculture Research Station facilities. From each spawning event, the following parameters were determined: number of floating and non-floating eggs, egg size, hatching success and larval total length. Eggs size and percentage of hatching obtained from F1 breeders (1.04 ± 0.10 mm and 90.5 ± 6.4%) were significantly higher when compared with wild breeders (0.97 ± 0.13 mm and 17.0 ± 12.7%). Although wild breeder spawns exhibited 2.7 ± 0.2 mm for larval total length, F1 breeder spawns presented 2.6 ± 0.2 mm. The wild and F1 breeder spawns exhibit a good egg and larval quality, indicating a promising starting point for a successful meagre hatchery production.

Draft Genome Sequence of Aliivibrio fischeri Strain 5LC, a Bacterium Retrieved from Gilthead Sea Bream (Sparus aurata) Larvae Reared in Aquaculture.

To shed light on the putative host-mediated lifestyle of the quintessential marine symbiont Aliivibrio fischeri, and on the symbiosis versus potentially pathogenic features of bacteria associated with farmed fish, we report the draft genome sequence of A. fischeri strain 5LC, a bacterium retrieved from gilthead sea bream (Sparus aurata) larvae.