Modulation of stress response and productive performance of Litopenaeus vannamei through diet

The high tolerance of Litopenaeus vannamei to a wide range of salinity (1–50 psu) makes this species an excellent candidate for culture under low salinity, decreasing shrimp epidemics and water pollution in some coastal areas. However, salinity levels outside the optimal range could impose several physiological constraints that would in turn affect growth and survival, particularly in the presence of additional stressors (e.g. high densities, handling practices, and hypoxia). Despite shrimp susceptibility to individual stressors has been widely addressed, information regarding response to chronic and acute stressors combined and its relation to diet is scarce. Thus, the aim of our study was to determine the effect of diet on the susceptibility to chronic (low salinity) and acute (hypoxia and escape response) stressors in terms of culture performance and physiological indicators. We evaluated overall performance during culture of L. vannamei at low salinity (6 psu), fed with an experimental diet with low protein and high carbohydrate content (26% protein and 6% fish meal plus probiotic mixture) and compared to a commercial formula with high protein and low carbohydrate content (40% crude protein and 20% fish meal without probiotic mixture). At the end of the rearing experiment, shrimp were exposed to two types of acute stress, hypoxia and escape. Biochemical (hemocyanin, total proteins, glucose, and lactate) and bioenergetic (adenylic energy charge and arginine phosphate levels) variables were measured to assess chronic stress response (salinity) and acute stress response (hypoxia or escape). The experimental diet resulted in higher muscle energy status that was not affected by low salinity, although lipid levels were lower under this condition. This diet partially counteracted the low performance at low salinity and promoted greater protein efficiency. Hypoxia induced strong hyperglycemic and lactate increase as response, whereas escape response was characterized by a depletion of arginine phosphate levels, with a stronger decrease in shrimp fed experimental diet, due to the high initial level of this reserve. Some data (glucose levels in hemolymph and lipids in hepatopancreas) suggest that shrimp under chronic stress conditions (low salinity and high densities) present a low ability to respond to subsequent acute stressors such as hypoxia or escape. This work indicates that diet can increase the energy status of shrimp, enabling them to overcome potential multifactorial stressors, which are common in farming systems

Gonadal development in male and female domesticated whiteleg shrimp Litopenaeus vannamei in relation to age, weight and grow-out conditions

Cultivation of whiteleg shrimp (Litopenaeus vannamei) is now entirely based on closed life-cycle populations, yet few studies have analyzed gonadal development in domesticated shrimp during grow-out in ponds. To determine the effect of age and weight on morphometric, histological, and biochemical variables associated with male and female gonadal development, shrimp from the same cohort, at ages of 6, 8, 10, and 12 months were examined using body weight as a covariable in an ANCOVA design. An additional comparison between two grow-out conditions in 1-year-old shrimp was done to separate the effect of size as a result of initial stocking densities. Age-related growth of gonads was clearly dependent on somatic growth for females but not for males, although differential somatic growth produced by stocking densities explained differences in growth of gonads for both sexes. Increase in oocyte diameter and differentiation associated with age and grow-out condition were independent of body weight. Age-related female gonadal development was accompanied by increases in lipid and protein concentrations, independent of body weight. Maturation of male reproductive organs (testicle, vas deferens, terminal ampoule, and spermatophore) was sequential and depended mainly on age, although body weight could explain differences caused by different grow-out conditions. An age-related decrease in concentration of lactate occurred in all male reproductive organs and could indicate a metabolic adjustment of sperm anaerobic metabolism and lactate clearance associated with gonadal development. We highly recommend waiting for optimal reproductive potential of females at 12 months to enhance spawning frequency and larval quality. At this age, body weight seems to be of secondary importance, although optimal conditions of cultivation are necessary to have adequate growth and balanced nutrition

Laboratory conditioning modifies properties of gills mitochondria from the Pacific oyster Crassostrea gigas

Although laboratory experiments allow greater control of environmental conditions than field studies, they have several drawbacks. To analyze physiological responses to forcing environmental variables, experimental conditions should mimic natural conditions as closely as possible. For filter-feeding organisms in particular, diet quality and quantity is one of the environmental parameters that can differ markedly between experimental and field conditions. In the hatchery, Pacific oysters, Crassostrea gigas, commonly show good physiological performance and growth on a mixed algal diet of Tisochrysis lutea, formerly Isochrysis aff. galbana clone Tahiti (T-Iso), and Chaetoceros calcitrans, presumably as it provides a good supply of essential polyunsaturated fatty acids (PUFA) as 20:4n-6, 20:5n-3 and 22:6n-3. The present study tests whether the fluctuating biotic and abiotic conditions in the field modify the structure and function of oyster mitochondria. One group of oysters was maintained in the intertidal zone, and the other group was fed the mixed diet in a nearby experimental hatchery under salinity and temperature conditions equivalent to those in the field. After 4 weeks of conditioning, the functional capacities and membrane lipid composition of gill mitochondria were measured. For essential polyunsaturated fatty acids, only the proportion of 20:5n-3 differed between field and laboratory oysters, and confirmed the capacity of the mixed diet T-Iso + C. gracilis, to provide the essential PUFA. Nevertheless, proportions of other FA (e.g., 22:5n-6 and non-methylene-interrupted FA) differed markedly between laboratory and field-conditioned oysters. Mitochondrial oxygen uptake, cytochrome c oxidase activity, content of cardiolipin and concentration of cytochrome b were significantly lower in laboratory-conditioned than in field-conditioned oysters. These results indicate that laboratory conditioning, although allowing similar growth and gonad maturation, only partially mimics conditions that allow C. gigas to maintain mitochondrial function. Although our experimental design cannot ascertain what difference between experimental laboratory and field conditions led to changes in membrane composition and mitochondrial function, differences in nutritional quality (other than known essential PUFA) and abiotic factors (e.g., oxygen availability, emersion or daily temperature fluctuations) had a major impact on mitochondrial properties in oysters

Seasonal variations of biochemical, pigment, fatty acid, and sterol compositions in female Crassostrea corteziensis oysters in relation to the reproductive cycle.

International audienceWild female Crassostrea corteziensis oyster (n=245) were analyzed over one year to understand the main ecophysiological events associated to gonad development. Different indicators (mainly biochemical) were analyzed to infer: i) utilization and accumulation of energy reserves (e.g. neutral lipids, carbohydrates, proteins; vitellogenin), ii) membrane components provided by the diet as essential nutrients and indicative of cell proliferation (e.g. highly unsaturated fatty acids linked to phospholipids, sterols), iii) indicators of food availability (chlorophyll a in water, pigments in tissues, specific fatty acids and sterols), iv) gonad development (e.g. gonad coverage area, vitellin). A PCA analysis was applied to 269 measured variables. The first PC (PC1) was composed of total carbohydrate and lipid concentration, percentage of esterified sterols, fatty acids specific of diatoms; 16:1n-7/16:0, 20:5n-3 in neutral lipids with positive loadings and non methylene-interrupted fatty acids (NMI) in neutral lipids with negative loadings. The second PC (PC2) was composed of 18:4n-3 in lipid reserves and the concentration of zeaxanthin, a pigment typical of cyanobacteria with positive loadings and the proportion of 20:4n-6 in polar lipids with negative loading. The third PC (PC3) was composed of gonad coverage area (GCA) and the concentration of vitellin. Variation in GCA confirms that gonad development began in April with an extended period of spawning and rematuration from April to November. The PCA further shows that a second period of minimal maturation from November to March corresponds to the accumulation of reserves (PC1) together with an initial high availability of food (PC2) at the beginning of this period. These two periods are in accordance with the classical periods of allocation of energy to reserves followed by gonad development reported for several mollusks

Specific regulations of gill membrane fatty acids in response to environmental variability reveal fitness differences between two suspension-feeding bivalves (Nodipecten subnodosus and Spondylus crassisquama)

International audienceBivalves' physiological functions (i.e. growth, reproduction) are influenced by environmental variability that can be concomitant with trophic resource variations in terms of quality and quantity. Among the essential molecules that bivalves need to acquire from their diet to maintain physiological functions, fatty acids (FAs) such as polyunsaturated fatty acids (e.g. 20:4n-6 (arachidonic acid), 20:5n-3 (eicosapentaenoic acid) and 22:6n-3 (docosahexaenoic acid)) have been described to play a critical role. The present study examined the FA composition of gill membrane lipids of two bivalve species, Nodipecten subnodosus and Spondyluscrassisquama, sampled in a coastal lagoon of the Northeastern Pacific (Ojo de Liebre, Mexico), at two contrasting locations (inner versus outer part of the lagoon) and at two different periods (February and August 2016). Spatiotemporal variations showed that FA composition of gill membrane lipids was highly correlated to FA composition of reserve lipids from digestive gland. This highlights the marked impact of the diet on FA composition of gill membranes. Interestingly, both species presented differences in the seasonal accumulations of plasmalogens and of particular FA that are not found in their diet (e.g. non-methylene interrupted FA, 22:4n-9trans, 20:1n-11), suggesting specific regulations of FA incorporation and lipid class composition in gill membranes to maintain optimal membrane function in their specific and changing environment. This study highlights the importance to characterize the spatial and temporal variability of food resources in order to apprehend the physiological consequences of environmental variability, as well as species differential regulation capacities in a changing world

Trophic ecology of suspension-feeding bivalves inhabiting a north-eastern Pacific coastal lagoon: Comparison of different biomarkers

WOS:000463281500015International audienceUnderstanding the nature and origins of food sources supporting coastal lagoon-inhabiting organisms is necessary to evaluate the ecological status of such ecosystems. The trophic ecology of a bivalve species Spondylus crassisquama was studied in the Ojo de Liebre lagoon (Baja California, Mexico), combining stable isotope (SI), fatty acid (FA) and sterol analyses along a transect under oceanic influences. The second objective of the study was to investigate if sterol compositions give complementary information to those obtained from FA and SI. Temporal and spatial patterns of the three biomarkers in bivalve tissues suggest oceanic inputs at the mouth of the lagoon, while the inner station was characterized by a contribution of local sources including an important role of micro heterotrophs. This study revealed that the association of lipid biomarkers provide higher taxonomic resolution of the spatiotemporal heterogeneity in nutrient sources influencing the trophic functioning of a large coastal lagoon

Metabolic responses of adult lion's paw scallops Nodipecten subnodosus exposed to acute hyperthermia in relation to seasonal reproductive effort

WOS:000562870700002International audienceIn marine ectotherms, reproduction is an energetically expensive process that affects their thermal window tolerance. For most species, the impacts of hyperthermia during gametogenesis have still not been addressed. Our aim was to assess the metabolic response of adult Nodipecten subnodosus scallops to thermal challenges at early development (spring) and advanced gonad maturation (summer). Scallops collected in both seasons were exposed to acute hyperthermia (26 and 30 degrees C, 24 h), maintaining a group of scallops at acclimation temperature (22 degrees C) as a control condition. During the summer, relatively low activity of hexokinase (HK), as well as low levels of ATP and GTP were found in the adductor muscle, suggesting a shift in energy investment for reproduction, although arginine phosphate (ArgP) levels were higher in summer scallops. Hyperthermia (30 degrees C) induced an increased energy expenditure reflected by a transitory enhanced oxygen consumption (VO2) and relatively high activities of HK and arginine kinase (AK). Moreover, a slight decrease in adenylic energy charge (AEC) was partially compensated by a decrease in ArgP. An increase in nucleotide by-products inosine monophosphate (IMP) and hypoxanthine (HX) indicated a thermal stress at 30 degrees C. Some of the responses to acute hyperthermia were more pronounced at advanced maturation stages (summer scallops), indicating a possible lack of energy balance, with possible implications in animals challenged to global warming scenario

Transcriptomic analysis of Pacific white shrimp (Litopenaeus vannamei, Boone 1931) in response to acute hepatopancreatic necrosis disease caused by Vibrio parahaemolyticus.

Acute hepatopancreatic necrosis disease (AHPND), caused by marine bacteria Vibrio Parahaemolyticus, is a huge problem in shrimp farms. The V. parahaemolyticus infecting material is contained in a plasmid which encodes for the lethal toxins PirABVp, whose primary target tissue is the hepatopancreas, causing sloughing of epithelial cells, necrosis, and massive hemocyte infiltration. To get a better understanding of the hepatopancreas response during AHPND, juvenile shrimp Litopenaeus vannamei were infected by immersion with V. parahaemolyticus. We performed transcriptomic mRNA sequencing of infected shrimp hepatopancreas, at 24 hours post-infection, to identify novel differentially expressed genes a total of 174,098 transcripts were examined of which 915 transcripts were found differentially expressed after comparative transcriptomic analysis: 442 up-regulated and 473 down-regulated transcripts. Gene Ontology term enrichment analysis for up-regulated transcripts includes metabolic process, regulation of programmed cell death, carbohydrate metabolic process, and biological adhesion, whereas for down-regulated transcripts include, microtubule-based process, cell activation, and chitin metabolic process. The analysis of protein- protein network between up and down-regulated genes indicates that the first gene interactions are connected to oxidation-processes and sarcomere organization. Additionally, protein-protein networks analysis identified 20-top highly connected hub nodes. Based on their immunological or metabolic function, ten candidate transcripts were selected to measure their mRNA relative expression levels in AHPND infected shrimp hepatopancreas by RT-qPCR. Our results indicate a close connection between the immune and metabolism systems during AHPND infection. Our RNA-Seq and RT-qPCR data provide the possible immunological and physiological scenario as well as the molecular pathways that take place in the shrimp hepatopancreas in response to an infectious disease

Energy metabolism of juvenile scallops Nodipecten subnodosus under acute increased temperature and low oxygen availability

High temperature increases energy demand in ectotherms, limiting their physiological capability to cope with hypoxic events. The present study aimed to assess the metabolic tolerance of juvenile Nodipecten subnodosus scallops to acute hyperthermia combined with moderate hypoxia. A previous study showed that juveniles exhibited a high upper temperature limit (32 • C), but the responses of juveniles to combined hyperthermia and low dissolved oxygen are unknown. Scallops were exposed to control conditions (treatment C: 22 • C, ~7.1 mg O 2 L − 1 or PO 2 156.9 mmHg), acute hyperthermia under normoxia (treatment T: 30 • C, ~6.0 mg O 2 L − 1 or PO 2 150.9 mmHg) or acute hyperthermia plus hypoxia (treatment TH: 30 • C, ~2.5 mg O 2 L − 1 or PO 2 62.5 mmHg) for 18 h. In T, juveniles exhibited an enhanced oxygen consumption, together with a decrease in adenylate energy charge (AEC) and arginine phosphate (ArgP), and with no changes in metabolic enzyme activity in the muscle. In TH, scallops maintained similar AEC and ArgP levels in muscle as those observed in T treatment. This response occurred along with the accumulation of inosine monophosphate and hypoxanthine. Besides, reduced citrate synthase and pyruvate kinase activities, enhanced hexokinase activity, and a higher octopine dehydrogenase/ lactate dehydrogenase ratio in the mantle indicated the onset of anaerobiosis in TH. These responses indicate that juvenile scallops showed tissue-specific compensatory responses regarding their energy balance under moderate hypoxia at high temperatures. Our results give an insight into the tolerance limit of this species to combined hyperthermia and hypoxia in its northern limit of distribution