Cold temperature is an effective method of achieving out-of-season reproduction and obtaining fry in the autumn. This study investigated the effects of low-temperature (12-16 °C) environment on the out-of-season reproduction of largemouth bass, particularly the delayed effects on ovarian development. During the period of delayed out-of-season reproduction, there was a significant reduction in the levels of serum sex hormones (FSH and LH) and their respective receptors (FSHR and LHCGR). Exposure to cold temperature significantly reduced the expression of gonadal development genes (IGF-1, GDF9, and CDC2) (P<0.05) and diminished the vascular network on the ovarian membrane, as confirmed by angiogenesis-related analyses. In lipid metabolism, AMH mRNA levels decreased overall, while HSD3B, FABP1, APOA1, and APOC2 initially increased before declining. Serum VTG levels decreased gradually with a slight increase post-spawning. These findings suggested that cold temperature delay ovarian development in largemouth bass by impacting sex hormone synthesis, angiogenesis, and lipid deposition. This insight enhances our understanding of out-of-season reproduction and guides the development of more effective reproductive techniques.

Suspension-feeding bivalves, including the oyster Crassostrea virginica, use mucosal lectins to capture food particles. For instance, oysters can increase the transcription of these molecules to enhance food uptake. However, the regulatory processes influencing food uptake remain unclear although likely involve neuropeptides. Information on the neuropeptidome of C. virginica is limited, hindering the comprehension of its physiology, including energy homeostasis. This study explored the genome of C. virginica to identify neuropeptide precursors in silico and compared these with orthologs from other mollusks. A special focus was given to genes with potential implication in feeding processes. qPCR was used to determine the main organs of transcription of feeding-related genes. To further probe the function of target neuropeptides, visceral ganglia extracts and synthetic NPF were injected into oysters to evaluate their impact on genes associated with feeding and energy homeostasis. A total of eighty-five neuropeptides genes were identified in C. virginica genome. About 50 % of these are suggested to play a role in feeding processes. qPCR analyses showed that visceral ganglia and digestive system are the main organs for the synthesis of feeding-related neuropeptides. Further, results showed that the transcription of several neuropeptide genes in the visceral ganglia, including NPF and insulin-like peptide, increased after starvation. Finally, the injection of visceral ganglia extracts and synthetic NPF increased the transcription of a mucosal lectin and a glycogen synthase, known to be involved in food capture and glucose storage. Overall, this study identifies key genes regulating oyster physiology, enhancing the understanding of the control of basic physiological mechanisms in C. virginica.

The use of anesthetic agents as pre-operatory treatment to pearl seeding surgery can be stressful to organisms and activate various physiological response mechanisms. This study evaluated some parameters of the systemic antioxidant and immune responses in red abalone (Haliotis rufescens) exposed to 0.25 mL L eugenol (EUB), 3.0 mL L phenoxyethanol (PEB) and CO at saturation, as well as in a control (CT) without anesthetic. Abalone were anesthetized for 45 min and, during the recovery stage, hemolymph samples were collected at 0.5, 1, 2 and 24 h. Total protein content (TP), superoxide dismutase (SOD), catalase (CAT) and myeloperoxidase (MPO) activity, as well as nitric oxide (NO) production, were evaluated in hemolymph cell-free fraction (HCF) and hemocytes lysate (HL). In addition, total hemocyte count (THC) was determined. In HCF, TP was significantly higher in abalone exposed to PEB than in the other treatments and CT at 0.5, 1 and 24 h. SOD activity in HCF was significantly higher in all treatments compared to the CT (1 h), while CAT and MPO activity was only significantly higher in abalone exposed to EUB compared to PEB at 1, 2 and 24 h. In the HL fraction, the percentage of SOD inhibition was significantly higher only in abalone anesthetized with EUB compared to the CT (0.5 h). These results suggest that the antioxidant activity of the species during the recovery phase from anesthesia was transient and restored after 24 h. Similarly, the immune response of H. rufescens at the systemic level was not altered by the anesthetics, suggesting that the species adequately tolerated the anesthesia process. This research provides evidence of the effects of anesthesia at the systemic level in red abalone for the proper selection of anesthetics for pearl culture.

Hibernation is accompanied by dramatic decrease of blood flow in many organs due to the increase of their vascular resistances. We compared the responses of mesenteric, renal, and cerebral proximal resistance arteries in summer active (SA) and winter hibernating (WH) ground squirrels and studied the signaling pathways of Rho-kinase and NO. Wire myography and Western blotting were used to assess the arterial responses and protein abundances. Basal tone and contractile responses did not differ between SA and WH squirrels in mesenteric and renal arteries, but were greatly increased in basilar arteries of WH compared to SA. Rho-kinase inhibitor abolished the differences in basilar artery basal tone and contractile responses between WH and SA squirrels, while the content of Rho-kinase II protein in the cerebral arteries did not differ between the groups. NO-synthase inhibitor increased basal tone level and basilar artery contractile responses only in SA but not in WH animals, so that the intergroup differences disappeared. The responses of basilar artery to the NO-donor and eNOS protein content did not differ between the two groups, while nNOS protein content was reduced in WH compared to SA. Therefore, the increase of basilar artery basal tone and contractile responses in hibernating animals is due to the increase of procontractile influence of Rho-kinase and the decrease of anticontractile influence of NO. Localization of high resistance in the hibernating brain at the level of proximal resistance arteries may be important for rapid restoration of cerebral blood flow upon arousal from hibernation.

The zig-zag eel exhibits both sexual dimorphism and sex reversal, making it crucial to understand the mechanisms of sex determination and differentiation. Additionally, the wild populations of the zig-zag eel are significantly declining, emphasizing the need for urgent conservation efforts. In this study, we identified 7 Dmrt, 62 HMG-box, and 73 TGF-β family members in the zig-zag eel genome. Evolutionary analysis revealed that the HMG-box and TGF-β families in the zig-zag eel are primarily characterized by purifying selection. Furthermore, we identified 52 differentially expressed genes between males and females, with more male-biased genes than female-biased genes within these three gene families. ZzDmrt2a was highly expressed in the ovary, while ZzDmrt2b was highly expressed in the testis. Interestingly, Zzgdf9, located on the Y chromosome, was significantly expressed in the ovary. Our results highlight the complexity of sex differentiation mechanisms and underscores the importance of further research to elucidate the specific functions and regulatory networks of these sex-biased genes. Such insights could inform breeding strategies in aquaculture, contributing to the conservation and management of the zig-zag eel.

The present study investigated the changes of expression and localization of PtVg mRNA, tissue Vg/ Vn concentrations, the contents of progesterone and 17ß-estradiol during the ovarian development of P. trituberculatus. The results showed that: 1) The most abundant mRNA levels of PtVg were found in stage IV, and hepatopancreatic PtVg mRNA was markedly greater than that in ovaries from stage II to stage V. The positive signal of PtVg mRNA was found in the follicular cells (FC), the cytoplasm of previtellogenic oocytes (PRO) and endogenous vitellogenic oocytes (EN), and hepatopancreatic fibrillar (F) cells and resorptive (R) cells. 2) The ovarian Vn contents reached the peak at stage V. In the hemolymph and hepatopancreas, the level of Vg/Vn markedly increased from stage II to stage IV. Immunohistochemistry findings confirmed that the PtVg protein was primarily distributed in the FC and the oocyte cytoplasm of late stages (II-V). 3) The highest levels of progesterone in the ovaries, hepatopancreas and hemolymph all appeared in stage II and then declined gradually from stage II to stage V. Ovarian 17β-estradiol concentration show an increasing trend from stage I to IV and remarkably decreased at stage V, while the peak levels of 17β-estradiol in hepatopancreas and hemolymph was found in stage III. 4) Positive correlations were found between ovarian and hepatopancreatic 17β-estradiol content and the corresponding Vg mRNA level, while significantly negative correlations were found between the tissue progesterone titers and the corresponding GSI or Vg/Vn contents during ovarian maturation. In conclusion, the vitellogenesis characteristics of P. trituberculatus are stage-specific, and most vitellogenin is produced by the hepatopancreas, which is also highly correlated to the changes of tissue 17β-estradiol content during the ovarian developmental cycle.

Anthropogenic pressures and climate change present growing challenges for cetaceans, as the combined effects of multiple stressors can jeopardize their welfare and survival. In this context, validating reliable individual welfare indicators is crucial for quantifying these impacts. This study aimed to validate a method for measuring cortisol and oxytocin from the epidermis of stranded striped dolphins (Stenella caeruleoalba) using enzyme immunoassays, while accounting for confounding factors such as epidermal layer and body location. The effects of different causes of death-'Peracute Underwater Entrapment' and 'Distress Associated'- along with biological factors, were examined in relation to epidermal hormone levels. Furthermore, the relationship between these hormone levels and markers suggesting an impaired welfare, was explored. Validation tests indicated that the method was effective in quantifying both epidermal cortisol and oxytocin concentrations. Specifically, epidermal cortisol levels showed strong correlations with both serum and blubber levels and were 6 times higher in emaciated individuals and 14 times higher in those with distress-associated deaths, supporting its use in assessing hypothalamic-pituitary-adrenal activity. Interestingly, results supported the validity of epidermal cortisol levels as markers of impaired welfare in dolphins, as they consistently increased across conditions assumed to negatively affect welfare but varying in terms of severity and duration. In contrast, epidermal oxytocin levels could not be validated as an indicator of the general oxytocin system nor as an indicator of welfare in this species. In conclusion, this study successfully validated epidermal cortisol as a reliable physiological indicator of welfare in striped dolphins, providing a promising tool for assessing individual and population-level welfare impacts. However, further research is needed to fully explore the potential role of oxytocin as a welfare biomarker in cetaceans.

The cyclopoid copepod species Apocyclops royi has attracted significant attention due to its importance in marine food webs and its role as a vital food source for many marine organisms, particularly marine fish larvae. This study aims to understand the activity patterns, osmoregulation mechanisms, and physiological adaptations of A. royi in response to acute decreasing salinities. In total three experiments were conducted. The first two experiments both investigated behavioural change and survival as a function of acute decreasing salinities in the range from 32 to 0, with steps of salinity reductions of five. The third experiment investigated the correlation between internal and external osmolality in A. royi, by using a novel method developed for the experiment. The first experiment indicated that A. royi behaviour and survival were not affected at salinities from 20 and higher. Surprisingly, some copepods were able to survive an acute decrease in salinity from 32 to 0. The second experiment utilized, for the first time for this copepod species, an in situ Multispecies Freshwater Biomonitoring system, to further observe A. royi's behaviour. The results showed that the system was able to monitor A. royi activity level. The system both documented that A. royi exhibit a statistically significant increase in activity levels in response to light. Furthermore, it provided knowledge about the temporal activity level of A. royi as a function of acute decreases in salinities, providing insights into that A. royi has an ∼3 h acclimatization time to an acute decrease from 32 to 0 salinity. In the third experiment, the osmolality of the copepods' body fluids with relation to external osmolality was examined using a vapor pressure osmometer. In this context a new method to extract body fluids from A. royi was developed. The body fluid osmolality of copepods exposed to three different salinities 10, 20 and 32 was examined. The results showed that A. royi is an osmoconformer at a higher salinity 32 but initiates hyperregulation at a lower salinity 10. Furthermore, it was observed that when copepods were exposed to a salinity of 10, 1000 individuals (stage: C5 or adults) were needed to obtain one sample of body fluid (10 μL) whereas when exposed to a salinity of 32, 3000 individuals were required to extract the same amount of body fluid. Overall, the findings demonstrated that A. royi has a high tolerance for acute decreases in salinity, showcasing behavioural adaptations and osmoregulatory capabilities, at extreme salinities. These results contribute to our understanding of copepod physiology and their ability to thrive in various habitats. Further research is needed to fully comprehend the physiological mechanisms underlying A. royi's adaptation abilities to acute decreases in salinity.

The round goby (Neogobius melanostomus) is a benthic fish species native to Central Eurasia but has colonized much of the waterways in the Laurentian Great Lakes in North America. While they are known to produce acoustic signals that aid in conspecific agonistic and reproductive interactions, the species does not possess a swim bladder and thus does not have any hearing specializations that would allow for sound pressure detection. Here, the auditory evoked potentials from saccular hair cells were characterized to determine the frequency response and auditory sensitivity of the saccule. Saccular potentials were recorded from the medial region of the saccular maculae during playback of single frequency acoustic stimuli (105-605 Hz). Auditory tuning curves based on both sound pressure (dB re: 1 μPa.) and particle acceleration (dB re: 1 ms) suggest that the saccule is most sensitive to 105 and 125 Hz and that the highest thresholds occurred at frequencies ≥205 Hz.

The prevalence of heatwave and hypoxia events and their devastating impacts on aquatic ecosystems and fishery resources reinforces the priority of research to address the resilience and adaption mechanisms to these two stressors in important fish species. However, our understanding of the development of cross-tolerance of these two stressors in fish still limited. Here, we investigated the impacts of prior heatwave exposure on hypoxia tolerance and the underlying mechanisms in silver carp (Hypophthalmichthys molitrix), a species of considerable ecological and commercial importance. Our results revealed that prior heatwave exposure significantly reduced the dissolved oxygen levels required to induce aquatic surface respiration (ASR) and loss of equilibrium (LOE) in juvenile silver carp, indicating the development of cross-tolerance to hypoxia. Physiologically, prior exposure to heatwaves significantly induced gill remodeling by triggering extensive apoptosis. These pre-existing physiological alterations and similar morphological alterations induced by subsequent hypoxia resulted in cumulative effects, leading to extensive gill remodeling under hypoxic conditions and thereby improving hypoxia tolerance. Molecularly, heatwave exposure modulated the expression of critical genes associated with hypoxia adaptation with tissue-specific responses. In the gill, heatwave exposure activated the hypoxia-induced factor (HIF) signaling pathway, increasing oxygen transport (VEGF-A, HB-β) and antioxidant gene expression (GPx, SOD2), facilitating rapid adaptation to hypoxia. In the liver, this exposure resulted in accelerated and enhanced gene expression of HIF-1α, anaerobic metabolism (GLUT-1, LDH-A), and heat shock protein (HSP70) under hypoxic conditions, contributing to improved adaptation. These results highlighted that prior exposure to heatwaves provided cross-tolerance to silver carp, bolstering their resilience to hypoxia through physiological gill remodeling and tissue-specific transcriptional adjustments. Our findings shed light on the intricate interactions of silver carp's thermal and hypoxic stress resilience, offering valuable perspectives for predicting and alleviating climate change impacts on aquatic life.

Although a giant Egyptian domestic non-migratory duck breed is phenotypically identical to the migratory Mallard, yet it is three times larger. The current study sought to determine the genetic and metabolic differences between this duck and Mallard, which arrives in Egypt in September for wintering and departs in March. Mitochondrial DNA control region (D-loop) was extracted, amplified, sequenced, and analyzed in both ducks. Both ducks were given a high-fat diet (HFD) for 6 weeks to assess their metabolic response to this diet. Polymorphism results indicated that the D-loop is highly variable and both populations expansion is balanced. The hierarchical analysis of molecular variants (AMOVA) and interpopulation difference parameters revealed significant genetic differentiation and minimal gene flow between migrant and resident populations. Phylogeny and Network analyses revealed that domestic ducks are a distinct group that separated from mallards. Physiologically, domestic duck blood and adipose tissue had a higher level of triglycerides and adipocyte volume than that of the depleting arriving migratory Mallard ducks, while leaving Mallard parameters were the highest, suggesting a high level of preparatory fat deposition and utilization before starting the trip. In response to HFD, the expression of FA uptake genes cd36, fabp1 was upregulated similarly in livers of domestic and migratory Mallard ducks, while the expression of lipid accumulation genes dgat2 and plin2 was higher in domestic than in migratory Mallards. However, the highest body mass and adipocytes volume gain was observed in the arriving migratory Mallards. In pectoral muscle, the expression of cd36 and fabp3 was higher in domestic than in leaving ducks, while in arriving Mallards, both genes were not upregulated in response to HFD. Dgat2 was upregulated only in domestic muscle, while lipid oxidation genes cpt1, lpl, and the controlling ppara were more upregulated in leaving Mallard. In conclusion, both ducks can be genetically and metabolically differentiated. Migratory mallards are more flexible and efficient in lipid metabolism than domestic ducks.

The occurrence of environmental hypoxia in freshwater and marine aquatic systems has increased over the last century and is predicted to further increase with climate change. As members of the largest extant vertebrate group, freshwater fishes, and to a much lesser extent marine fishes, are vulnerable to increased occurrence of hypoxia. This is important as fishes render important ecosystem services and have important cultural and economic roles. Evolutionarily successful, fishes have adapted to diverse aquatic freshwater and marine habitats with different oxygen conditions. While some fishes exhibit genetic adaptions to tolerate hypoxia and even anoxia, others are limited to oxygen-rich habitats. Recent advances in molecular epigenetics have shown that some epigenetic machinery, especially histone- and DNA demethylases, is directly dependent on oxygen and modulates important transcription-regulating epigenetic marks in the process. At the post-transcriptional level, hypoxia has been shown to affect non-coding microRNA abundance. Together, this evidence adds a new molecular epigenetic basis to study hypoxia tolerance in fishes. Here, we review the documented and predicted changes in environmental hypoxia in aquatic systems and discuss the diversity and comparative physiology of hypoxia tolerance in fishes, including molecular and physiological adaptations. We then discuss how recent mechanistic advances in environmental epigenetics can inform future work probing the role of oxygen-dependent epigenetic marks in shaping organismal hypoxia-tolerance in fishes with a focus on within- and between-species variation, acclimation, inter- and multigenerational plasticity, and multiple climate-change stressors. We conclude by describing the translational potential of this approach for conservation physiology, ecotoxicology, and aquaculture.

Bird nests of coastal or inland breeding birds can temporarily flood during high tides or storms. However, respiratory physiological disruption of such water submersion and implications for post-submergence survival are poorly understood. We hypothesized that respiratory physiological disturbances caused by submersion would be rapidly corrected following return to normal gas exchange across the eggshell, thus explaining survival of nest inundation in the field. We further hypothesized that the chicken embryo prior to hatching will develop the ability to recover from acid-base disturbance. We exposed day 15 embryonated chicken eggs (a well-studied point 3/4 through development) to half- or full submersion in water (producing moderate and severe hypoxia, respectively) or in mineral oil (anoxia) for periods of 2-24 h to create varying degrees of submersion-related respiratory and acid-base disturbances. Egg submergence was followed by up to six hours in air to determine the extent and rate of physiological recovery. Arterialized blood PO and [lactate], acid-base and hematology were measured at frequent intervals (5 min to 2 h depending on tested variable) both during submersion and air recovery. Submersion in mineral oil - eliminating all gas exchange - proved lethal at two hours. Yet, calculated embryonic oxygen stores suggest submerged embryos should be able to maintain pre-submergence oxygen consumption for only ∼15 mins, suggesting a possibly adaptive immediate decline in metabolism upon submergence. Half- or full submergence in water created blood acid-base disturbances within as little as 5 min, with partial recovery towards the end of 24 h of submergence. Six hours of subsequent air recovery fully restored acid-base homeostasis. Hematological changes that appeared within 5 min of submersion - primarily red blood cell swelling - were eliminated within 1 h following return to air. Importantly, these data indicate a surprising resilience of the chicken embryo to temporary elimination of normal gas exchange which, if evident in other species, provides underlying mechanisms for surviving nest inundation.

Our previous studies revealed a mating attractant or possibly a pheromone released from molting reproductive mature female prawns, Macrobrachium rosenbergii, stimulates the expression of insulin-like androgenic gland hormones in a co-culture system. The released attractant is perceived by olfactory receptors with setae located on the short lateral antennules (slAn), which connect to the olfactory neuropil in the central nervous system (CNS) of male prawns. This neural signaling propagating through the CNS is mediated by at least four neuropeptides, namely neuropeptide F (NPF), short NPF (sNPF), tachykinin (TK), and allatostatin-A (ATS-A) whose transcripts have been detected in the present study. These deduced sequences, along with their conserved domains, serve as signatures of the identified neuropeptides, which were then compared with those found in other crustaceans and insects, whose nucleotide sequences were obtained from the nucleotide database. RT-PCR identified the expressions of the transcripts encoding these neuropeptides in the CNS. In situ hybridization specifically localized these transcripts in olfactory-associated neurons of cluster 9/11 of the deutocerebrum. Quantitative real-time PCR was used to quantify the expressions of the transcripts in response to the female attractants under different co-culture conditions: males with molting females (G1), males with intermolt females (G2), and slAn ablated males with molting females (G3). The transcripts were significantly increased on days 4-8 in the brain (Br) of males in G1 but not in G2 and G3. This suggests that expressions of the transcripts encoding the neuropeptides are associated with the perception of female mating pheromones through the slAn. This study is the first to show that female mating chemicals regulate the expressions and abundance of the olfactory neuropeptides, thus providing valuable insights for manipulation of mating of this species in aquaculture production.

This work aimed to investigate the response of cholecystokinin (CCK) to starvation and its impact on food intake and the reproductive axis of the tilapia Oreochromis mossambicus. The fish subjected to 21 days of starvation showed a significant decrease in CCK immunoreactivity in the hypothalamus, pituitary gland, and intestine. The administration of injections of 0.5 and 5 μg of sulfated CCK-8 (CCK-8S) over 21 days resulted in a significant, dose-dependent decrease in food consumption. Administration of a high dose of CCK-8S (5 μg) caused a substantial decrease in the number of various spermatogenic cells, the intensity of androgen receptor immunoreactivity in the testis, and the percentage area of GnRH-immunoreactive fibres in the pars distalis of the pituitary gland (PPD), concurrent with a significant decline in serum levels of luteinizing hormone (LH) and 11-ketotestosterone (11-KT). Moreover, CCK-8S treatment markedly reduced the in vitro testicular 11-KT level. The findings indicate for the first time that CCK influences hypothalamic GnRH release into the pituitary gland, resulting in the inhibition of LH release from the pituitary and affecting testicular spermatogenesis, androgen receptor protein expression, and steroidogenesis in teleosts. In addition, CCK may also directly affect testicular steroidogenesis.

In a previous study, we demonstrated successful regeneration of Atlantic salmon gill tissue following up to 50 % filament resection. The present study explored 1) the capacity of gill tissue to regenerate following more severe trauma, 2) if regeneration potential varies across regions of the arch, and 3) how tissue loss impacts the physiology of neighboring unresected filaments. Fish were divided between two resected groups and a control non-resected one. In resection group-1, fish underwent 50 % and 75 % resection in the ventral and medial-dorsal regions of the first arch, while in resection group-2, the location of resection levels were reversed. The degree of filament regeneration and physiology of unresected filaments were measured at 4, 12 and 20 weeks-post-resection (WPR). Overall, the degree of regeneration was significantly higher in 50 % resected filaments relative to 75 % resected filaments. The degree of regeneration did not differ significantly between the resected groups for either of resection levels, suggesting negligible impacts of filament location on arch on regeneration. The concentration of oxidized glutathione (GSSG), total glutathione (GSH), and citrate synthase activity (CSA) in intact filaments were comparable between resected and control fish at both 4 and 20 WPR. However, GSH concentration varied among resected fish with those exhibited higher GSH in intact filaments showed lower regeneration of 50 % resected filaments at 20 WPR. Our results indicate that gill tissue loss exceeding 50 % may significantly impair regeneration and that this level of tissue loss is not associated with a compensatory response (e.g. GSSG, GSH, CSA) of neighboring gill tissue.

Fish are ectothermic animals with temperature playing a key role in their health, growth and survival. Greater occurrence of heat waves and temperature extremes, as a result of global climate change, has the potential to impact both wild and farmed populations. Within aquaculture, production is threatened by a multitude of stressors, including adverse temperatures. The propensity for environmental temperature during early embryo development to influence later life transcriptomic responses has been observed in numerous animal species, and, if harnessed, could provide a method for inducing phenotypic changes in adult aquaculture species. We hypothesise that exposure of rainbow trout embryos to temperature stress results in alterations to transcriptional responsiveness upon re-exposure later in life. To test this hypothesis, we exposed embryos to a range of different heat shock treatments during early development and then analysed their response to thermal stress at five days post hatch (dph), in comparison to naïve fish that experienced no early development heat shock. Hsp70a and hsp70b transcription was measured (using RT-QPCR) as a biomarker for thermal stress response. Significantly greater transcriptional induction of hsp70a in response to post-hatch thermal stress was found in heat shocked larvae compared to naïve larvae (p = 0.0085). The timing, intensity and duration of the initial heat shock was not found to statistically influence the alteration of hsp induction when compared to that of naïve larvae. Together, these results support our hypothesis that heat shock during early development has the potential to affect responsiveness to the same stressor later in life. Future studies should focus on understanding whether this could be utilised to increase robustness of fish in aquaculture.

This study presents a comprehensive examination of the physiological adaptations of white shrimp (Penaeus vannamei) to low-salinity conditions and evaluates the effects of supplementing dietary glucose on disease resistance. Compared to the control group, shrimp cultured at a salinity of 4 psu exhibit significantly elevated expression levels of adenosine 5'-monophosphate-activated protein kinase (AMPK) in the hepatopancreas, which leads to increased energy expenditure and a corresponding reduction in resistance to infection by Vibrio alginolyticus. The suppression of AMPK via dsAMPK treatment markedly enhances disease resistance. Moreover, shrimp raised in low salinity conditions exhibit downregulation of mTOR-associated molecules, including Lipin-1 and hypoxia-inducible factor 1-α (HIF-1α), both of which are essential for immune regulation. Metabolic assessments revealed reduced ATP levels and disrupted ATP/AMP and ATP/ADP ratios, indicating energy imbalance under low salinity stress. Notably, supplementing the diet with 1 % glucose significantly increased glycogen reserves and ATP content, stabilized hemolymph glucose levels, and upregulated glycolysis-related genes, thereby optimizing energy metabolism and enhancing resilience to stress. This study underscores that AMPK activation in response to low salinity conditions leads to increased energy expenditure, which in turn lowers disease resistance. Furthermore, it underscores the critical role of strategic dietary management in maintaining energy homeostasis and improving disease resistance in white shrimp under stressful environmental conditions associated with climate change, offering valuable insights for aquaculture nutrition strategies.

Climate change will increase the frequency and severity of temperature extremes. Links between host thermal physiology and their gut microbiota suggest that organisms' responses to future climates may be mediated by their microbiomes, raising the question of how the thermal environment influences the microbiome itself. Vertebrate gut microbiomes influence the physiological plasticity of their hosts via effects on immunity, metabolism, and nutrient uptake. The gut microbiota of ectothermic vertebrates in particular are responsive to long-term, sub-lethal gradual increases in environmental temperature. Whether and how the gut microbiota respond to brief exposure to temperatures at the upper limit of host physiological tolerance (CT) is poorly understood but could have downstream effects on host fitness. We assayed the CT of wood frogs (Lithobates sylvaticus) from 15 populations across a 10° latitudinal gradient. We then characterized the gut microbiota of juveniles at two time points following exposure to CT. Frogs from higher latitudes had lower thermal tolerance (lower CT) than those from lower latitudes. Unexpectedly, exposure to upper survivable temperature had little to no detectable effect on the frogs' microbiota richness, stability, or composition. Instead, we found a strong effect of time in which frogs kept in recovery conditions for four days had less diverse, but more stable gut microbiota than those that had recovered for only one day, regardless of CT exposure. We conclude that while wood frogs from higher latitudes have reduced thermal tolerances than those from lower latitudes, their microbial communities are largely unaffected by brief exposure to high temperatures at the edge of their physiological limits.

The crustacean cuticle is a composite material acting as a shell, but also linked with other physiological functions as respiration, locomotion or reproduction. The present study aimed to characterize for the first time the cuticle properties of the marine prawn Palaemon serratus using thermal (TGA) and chemical (FTIR, ICP-AES) techniques. The use of native lyophilized cutiles also enabled to estimate the complexity of the cuticle structure of P. serratus. Hence, the prawn cuticle was found to be composed of bound water at 14 %, Light macromolecules at 27 %, heavy macromolecules at 17 % and inorganic elements at 42 %. This composition appeared to be similar to that of other swimming crustaceans, suggesting an adaptation of the cuticle structure in line with the ecology of the species. Then, thermal and chemical techniques were applied to characterize the structure changes of the cuticle induced by i) the moult cycle and ii) formic acid treatment. The moult cycle influence assessment revealed that the physicochemical properties were mainly modulated during postmoult, reflecting both the cuticle mineralization and tanning. Then, formic acid treatment led to cuticle alterations, related to the dissolution of amorphous minerals, which were detected by TGA, FTIR and ICP-AES. With these results, the assessment of cuticle properties using a combination of thermal and chemical techniques appeared to be interesting to monitor changes in cuticle structure in a dynamical context.

Early life telomere length is thought to influence and predict an individual's fitness. It has been shown to vary significantly in early life compared to adulthood. Investigating the factors influencing telomere length in young individuals is therefore of particular interest, especially as the relative importance of heredity compared to post-natal conditions remains largely uncertain. Adélie penguins are eco-indicators of the Antarctic ecosystem and their population are currently undergoing variable trajectories due to climate change. Here, we conducted a correlative study to investigate how telomere length was influenced by external and internal factors in Adélie penguin chicks. We found that most of the parameters we tested, including sex, body mass, brood size and hatching order as well as parental foraging trip duration, did not significantly influence chick telomere length at 32 days. However, siblings had similar telomere length, suggesting that hereditary factors play a stronger role in determining telomere length at this stage compared to the post-natal environment. In addition, telomere length and oxidative damage did not directly correlate but did interact in a complex way mediated by chick mass. High levels of oxidative damage were associated with longer telomeres in heavy chicks, whereas they were associated with shorter telomeres in light chicks. Although this mass-dependent relationship between telomere length and oxidative damage needs to be confirmed in future studies, it could reflect two different scenarios: (1) short telomeres may mimic the cost of poor nutritional conditions and oxidative damage in light chicks; (2) long telomeres may be maintained despite high oxidative damage in heavy chicks thanks to optimal nutritional conditions.