Freshwater prey rely on chemosensory information, such as predator dietary cues, to accurately assess local predation risk. Climate change is increasing the frequency of multiple environmental stressors that can disrupt how prey detect and respond to such cues, yet few studies have examined how stressors affecting different sensory modalities interact to shape antipredator behaviour. Here, we tested how paired stressors alter prey responses to predator dietary cues. Trinidadian guppies were exposed to two stressor combinations (warming + acidification and warming + turbidity) and received either predator dietary cues from Jack Dempsey cichlids or a water control. We then assessed shoaling index and area use as indicators of antipredator behaviour. Overall, increasing stressor intensity reduced antipredator responses, regardless of the sensory modalities affected. Our study highlights the need to examine a broader range of chemical cues and to better understand how multiple stressors shape predator-prey interactions in freshwater ecosystems.
Consequent upon growing concerns about the use of synthetic hormones, including melatonin, to improve fisheries and aquaculture, this study evaluated the effects of melatonin on the oxidative stress biomarkers of juvenile African catfish. One hundred and thirty-five fish were randomly assigned to groups receiving 0, 10, and 30 mg/L of melatonin in a static renewal system for 14 days, followed by seven days of melatonin withdrawal. Standard bioassays were used to quantify changes in plasma antioxidant and liver oxidative stress enzymes. The results showed significant duration- and concentration-dependent increases in plasma alanine transaminase, aspartate transaminase, and alkaline phosphatase levels compared to control groups (p <= 0.05). Contrarily, there were significant duration- and concentration-dependent reductions in liver superoxide dismutase and catalase, along with significant increases in malondialdehyde and glutathione activities (p <= 0.05). Interestingly, many of these changes persisted after melatonin was removed. These suggested that exogenous melatonin profoundly affected oxidative stress enzymes in juvenile catfish.
At present, very little is known about inflammatory mechanisms in the crustacean intestine. It could be driven by some evolutionarily conserved molecules, such as endogenous gasotransmitters (viz. NO/iNOS and H2S/CBS) and signalling components (viz. NF-& kcy;B/p65, Nrf2 and p38MAPK). To detect their tissue distribution and cellular localization in midgut, the freshwater crayfish Procambarus clarkii was used as a model organism and immunohistochemical (IHC) staining was performed. Data were representative of three independent experiments, each with n = 5. Results indicated that (1) both NO and H2S were present in midgut tissue, and iNOS and CBS could be responsible for their generation; (2) NOS-like immunoreactivity occurred primarily in the nucleus of adluminal epithelium, but the positive signals of CBS were mainly present in the cytoplasm; (3) NF-& kcy;B/p65 and p38 MAPK were diffusely distributed in the surface epithelium and lamina propria while Nrf2 densely lied in the nucleus of adluminal epithelium; (4) the positive signals of p38MAPK were more widely distributed than its phosphorylated form (p-p38MAPK), and p-p38 immunoreactivity was only observed in the nucleus but not in the cytoplasm. The epithelial cells and the molecules they produce might play a crucial part in mucosal immunity in crayfish gut.
Serrivomerid eels (Anguilliformes, Serrivomeridae) are present in the mid-latitude mesopelagic zone worldwide along with other mid-water eels. Nemichthyidae eels reportedly used vertically oriented body positions in the Atlantic Ocean, and submersible observations of vertical eels at the West Mariana Ridge (WMR) and southwestern Indian Ocean were mistakenly suggested to be nemichthyid eels. New up-close WMR observations in this study (May 2017) and examination of previous videos indicate that these vertical eels are serrivomerid eels and not nemichthyids, which have been seen behaving differently in underwater vehicles near Japan and elsewhere. During the five dives of the Shinkai 6500 Submersible (19-24 May 2017) made in a narrow study area to search for spawning anguillid eels along the WMR, at least seven vertically oriented eels were observed during three of the daytime dives at 650-850 m depths. Video recordings were obtained of four eels at 705-850 m during two dives (5.2-6.0 degrees C, salinity 34.5), and one was observed up-close at 850 m, with still camera images taken. This enabled confirmation that they belonged to the family Serrivomeridae, and likely the genus Serrivomer. There were two eels observed in the head-down and five in a head-up orientation, and one had a swollen abdomen, possibly from prey ingestion or developed gonads. Mesopelagic fishes, a large octopod, crustaceans, and gelatinous zooplankton were also observed at these depths where only a small amount of light reaches, so the vertical body orientation posture may be related to prey detection. Trichurids and some other fishes also use vertical body orientations, but existing video observations of nemichthyids do not show them using this type of behavior. Previously reported Atlantic observations were likely serrivomerids that appeared very slender and longer in comparison to images of specimens due to the ends of serrivomerid jaws breaking off during net capture.
In early austral autumn of 2002, Salpa thompsoni feeding rates and growth were assessed by incubation salps with two C14-labeled cultures of green algae Dunaliella maritima and Platymonas viridis. Daily carbon ingestion rates of blastozooids within the mass range of 0.9-28.3 mgC ind.-1 ranged from 2.8 to 60.3% of body carbon mass and were the function of the experimental food concentration nearly regardless of the individual salp mass. The absolute growth of salps was positively related to the salp size ranging from 0.64 to 6.50 mu gC ind.-1day-1 and from 0.02 to 1.56 mu gC ind.-1day-1 in oozooids and blastozooids, respectively. The linear individual length increase ranged from 0.33 to 1.93 mm day-1 and from 0.29 to 0.85 mm day-1 in blastozooids and oozooids. The mass-specific metabolic values (filtration, ingestion and growth) of salps under experimental conditions depend on food concentrations and the salp biomass, but weakly on their size.
Cells possess homeostatic mechanisms to regulate functions under stressful conditions. Among these mechanisms is the hypoxia-inducible factor (HIF). We aimed to characterize the expression of the HIF alpha protein in the crayfish brain, a putative pacemaker in this species, to determine if it exhibits a rhythm. Crayfish Procambarus clarkii were acclimated to a 12:12 light-dark cycle (LD 12:12), while others were kept in constant darkness (DD) for an additional 72 hours, in both conditions, being killed at six time points. The brains were processed by western blot using a primary anti-HIF-1 alpha antibody. Under LD, HIF alpha levels showed no significant daily variations. However, COSINOR analysis showed a bimodal rhythm. In the DD condition, significant differences were observed revealed a circadian rhythm. Our findings demonstrate that HIF alpha in the crayfish brain exhibits a circadian rhythm, suggesting its role as a master regulator in the circadian system feedback loop of the of these animals.
Zebrafish (Danio rerio) experience daily temperature variations that align with light-dark cycles. Opsins mediate vision and light perception and can also act as thermosensors. We examined whether low temperature (23 degrees C) modulates melanopsin gene expression in light-exposed and non-exposed organs. At 23 degrees C, the brain showed strong upregulation (similar to 10x) of opn4x1 and opn4x2 during the light phase, and widespread downregulation (similar to 6x) of almost all melanopsin genes during the dark phase. In the eye, opn4m1, opn4m2, and opn4m3 were reduced (similar to 3x) during light phase. Liver melanopsins displayed different expression patterns at 23 degrees C, with up- and downregulation (similar to 10x). All five muscle melanopsins were downregulated (2-10x) at 23 degrees C during the light phase, and opn4m3, opn4x1, and opn4x2 during the dark phase (2-5x). In addition to the photoperiod, we concluded that low temperature also affects melanopsin expression in adult D. rerio, in an organ- and daily time-dependent manner.
Global warming disrupts freshwater ecosystems, affecting the movement of vagile aquatic insects and their Functional Feeding Groups (FFGs), key to nutrient cycling and energy flow. This study hypothesized that predators would be less sensitive to thermal stress than collectors, scrapers, and shredders, leading to minimal movement changes. Using a cost-effective video-tracking system, we analyzed four movement variables under three levels of thermal stress. Results showed varied FFG responses, particularly under transitional heated-water conditions. Collector-filterers and shredders exhibited significant changes in total path length and movement tortuosity, while speed-related variables remained largely unaffected. Strong correlations were observed, except among gatherers under the highest temperature. The experiment suggests that warming may constrain point-to-point movement, with distance-related variables proving the most reliable indicators of sensitivity. Collectors, scrapers, and shredders showed greater distance reductions than speed changes, highlighting critical functional and trophic shifts in microhabitat dynamics under global warming.
Stress coping styles refer to the behavioral and physiological strategies used by animals to deal with challenges, which can influence their capacity for response and learning. We explored differences in learning capacity among tambaqui individuals classified by stress coping style. Twenty-four animals were classified as proactive (7.78 +/- 2.39 cm; 7.72 +/- 2.34 g) or reactive (7.68 +/- 0.51 cm; 6.98 +/- 1.32 g). For 15 days, the fish were tested in a T-shaped maze, where a visual marker, accompanied by food, was used to measure learning. The results indicated that both groups were unable to associate the visual marker with the food, suggesting that coping style did not influence associative learning. Although reactive animals showed longer latency time in the first 2 days, there were no differences in the subsequent days. Additional studies are needed to better understand how these stress coping styles may affect tambaqui's cognitive ability.
Serotonin (5-HT) is involved in arousal and defensive responses, both of which represent modulators of attention and orienting. Orienting responses (ORs), considered as a unit of attentional processing, are elicited by novel innocuous stimuli, differ from defense reflexes (DR)s, as the latter are elicited by painful and threatening stimuli. When zebrafish (Danio rerio) are exposed to a conspecific alarm substance (CAS), visual stimuli elicit a DR instead of ORs, suggesting a state of hypervigilance. CAS elicited an OR-to-DR shift, as shown both by the shift from an approach to an escape response when the stimulus was turned on and by the changes in directional focus. Both pCPA and 5-HTP attenuated the CAS-elicited OR-to-DR shift . While pCPA did not alter ORs in animals which were not exposed to CAS, 5-HTP abolished those responses, suggesting that the serotonergic tone is important in regulating the general arousal levels in zebrafish.
Larval development and subsequent settlement behaviour are important aspects which determine the persistence of sessile benthic organisms on shallow water tropical and subtropical coral reefs. However, only limited studies have been performed on the early-life histories of soft corals in Okinawa, Japan. In this study, we describe the development and settlement pattern of collected spawn materials from two Sclerophytum species and the larvae of a brooding Heteroxenia sp. from Okinawa Island, Japan. Results showed that for the brooding Heteroxenia sp., planulae can metamorphose and fuse at the pelagic stage, and have very low settlement rates on rubble substrates with crustose coralline algae (CCA). On the other hand, the planulae of the two Sclerophytum species have variable survival probability, but both mainly settle on rubble with CCA. These results highlight the differences in larval development and subsequent settlement behaviour and periods among soft coral species. This also serves as the first report describing the larval behaviour and settlement of these species in the subtropical region of Okinawa, Japan.
Changes in water temperature may have profound effects on physiology, metabolism, and fish behaviour. However, much of the existing research is based on relatively short-term experiments. In the context of climate change, where water temperatures are increasing seasonally, and the frequency and duration of extreme heatwave events are rising, incorporating longer exposure periods will provide a better understanding of the potential effects of warming on marine species. Here, we tested the effects of prolonged exposure to elevated temperature on broad-nosed pipefish, Syngnathus typhle. Fish were exposed to ambient (20 degrees C) and high (24 degrees C) temperatures for a four-month period, during which activity levels, growth and survival were monitored. Fish under high temperature were less active when compared to fish under ambient temperature, grew less, and survival was dramatically decreased. These findings have significant implications for the long-term sustainability of broad-nosed pipefish populations, as the species may struggle to adapt to future ocean conditions.
Our goal was to use the energy budget as a tool to evaluate the effects of salinity (20, 25, 30, 35 or 40 parts per thousand) and ocean acidification (pH 8.0 or 7.3) in Penaeus vannamei. We assessed the energy budget a range of physiological processes (ingestion, defecation, growth, metabolism, excretion, energy substrate, hepatosomatic index, and osmoregulation). In general, salinity had an accentuated effect than pH, as it altered nearly all physiological parameters, including the energy channeled into growth (up to -56%). Reduced pH also affected the energy budget: increased energy lost in feces (25 and 40 parts per thousand: +21% and 13%, respectively), excretion (25 parts per thousand: +55%), and metabolism (20 parts per thousand: +58%). Furthermore, acidified pH increased oxygen consumption by 60%, which may be related to higher energy expenditure. In conclusion, the energy budget can be a valuable tool for assessing the impacts of environmental stressors and the salinity has an accentuated effect than the ocean acidification predicted.
Symsagittifera roscoffensis forms a photosymbiotic relationship with the alga Tetraselmis convolutae within the intertidal zone. Juveniles lack algal symbionts at birth and acquire them from the environment. Requiring light for photosynthesis, they position themselves within the water column while also balancing the risk of being washed away. To understand their behavioural adaptations, we conducted experiments on their movement in response to algal cues (chemotaxis), light gradients (phototaxis), and mechanical vibrations. Aposymbiotic juveniles showed three times more positive displacement towards algae. Adults exhibited positive phototaxis but retreated from high light intensity. When introduced to a column with a light source, the worms remained just below the surface. In the mechanical vibration experiment, worms only descended when vibrations exceeded a threshold. These findings suggest that S. roscoffensis has chemotactic abilities crucial for acquiring algae and acquires light for photosynthesis while minimizing dispersal risk and photoinhibition, facilitating its life cycle in the intertidal zone.
The activity of liver catalase and brain acetylcholinesterase was assessed in rainbow trout (Oncorhynchus mykiss) after 7- and 14-day exposure to a six-metal mixture at the maximum permissible concentrations accepted for inland waters in the EU (2013/39/EU; 2008/105/EC) (Zn - 0.1, Ni - 0.034, Cu - 0.01, Cr - 0.01, Cd - 0.0015 and Pb - 0.014 mg L-1) and to the same six-metal mixtures with tenfold reduced concentration of Cu and Cr ions. A statistically significant increase of up to 26% of catalase and 52% of acetylcholinesterase activity was observed in rainbow trout after 7 days of exposure to the six-metal mixture at the maximum permissible concentrations in comparison to a control group. After 14-day treatment, neither CAT nor AChE showed significant response to all tested metal mixtures. The six-metal mixture with the tenfold reduced concentration of Cr increased brain AChE activity in O. mykiss after 7 days of exposure (35%). Enhancement of catalase activity caused by the mixture of the six metals at the maximum permissible concentrations and the increased acetylcholinesterase activity in response to the same metal mixture and mixture with tenfold reduced Cr concentration after 7 days of exposure indicates the induction of oxidative stress and disturbance of cholinergic system homeostasis respectively.
The aim of this study was to evaluate the reproductive aspects of Nile tilapiaclassified by personality traits. Through the environment test 16 males (8 Bold - BM and 8 Shy - SM) (110.5 +/- 23.8 g) and 32 females (16 Bold - BF and 16 Shy - SF) (87.5 +/- 19.3 g) were microchipped. Every seven days, were selected and relocated in mating tanks at a 2:1 female:male ratio, according to the treatments: BFBM, BFSM, SFBM and SFSM. The breeding management lasted eight weeks, after which semen was collected and analyzed, using CASA software. Offspring resistance was tested after complete absorption of the yolk sac by air exposure . Breeders of the same personality traits spawned more frequently, with the greatest amount of spawning being for BFBM and the lowest for BFSM. Total and relative fecundity were higher for SF. However, the percentage of newly hatched larvae, egg weight and volume of yolk sac were higher for BF. In males, only the Curvilinear Velocity and Straight-line Velocity were influenced by personality traits. The offspring of BF showed greater resistance to the stress test. Personality traits have an influence on reproductive parameters related to females than to males. .
With the features as global distribution and all depths dwelling, holothurians function an ideal model for the study of deep-sea adaptation. Acquisition of high-molecular-weight DNA is the basic requirement for molecular biology analyses. However, extraction of high-molecular-weight DNA from deep-sea holothurians is difficult by degradation and contamination. Here, we presented a modified CTAB (lysis buffer with cetyl trimethyl ammonium bromide) method and compared its extraction efficiency for deep-sea holothurians with other five common methods, i.e. the Tiangen Biotech kit, Qiagen kit, Omega Bio-tek kit, Sangon Biotech kit, and SDS (lysis buffer with sodium dodecyl sulfate). Based on the results of yield, integrity, and purity, we found that the modified CTAB method is more suitable to extract high-quality DNA for deep-sea holothurians, with a large amount of yield, minimized degradation, and higher purity. This study provides a high-quality DNA of deep-sea holothurians for genome sequencing and further studies.
Green abalone (Haliotis fulgens) experienced severe biomass losses and massive mortality due to short-term marine climatic extremes. We studied green abalone behavior and energy expenditure in response to environmental stress. Acclimatized juveniles were subjected to hyperthermia (26?), hypoxia (1.0 mg O2 L-1), the combination of both, and control conditions (18? and oxygen saturation) using an automated system. The movement parameters of organisms were recorded by labeling and filming them, and the respiration rate was measured in hermetic chambers. There were differences in gross and net distance and velocity between the control and the combined stressors. Respiration was raised by hyperthermia, lowered by hypoxia, and further reduced by the combined stressors. All abalone that left the shelter during the night returned by daylight, while hypoxia and hyperthermia reduced this number. Research on environmental stress and movement strategies could lead to a more objective stress proxy.
Penaeus vannamei, experiences hypoxia in its natural habitat and in aquaculture. Under hypoxia, cells enhance anaerobic energy production through glycolysis dependent on the up-regulation of glycolytic enzymes including glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in gills. In vertebrates, GAPDH translocates into the nucleus and displays "moonlighting" functions including apoptosis. These alternative localizations and functions have not been described in crustaceans. We examined the effect of severe hypoxia and GAPDH silencing by RNA interference (RNAi) on its mRNA expression localization and glycolytic activity in P. vannamei gills. Expression and cytosolic activity were up-regulated only in hypoxia-exposed shrimp, but not in hypoxia-silenced specimens. GAPDH was immunodetected in cytosol and nucleus regardless of oxygen conditions. Hypoxia and RNAi decreased activity in cytosol and nucleus without affecting protein abundance, which suggests that nuclear GAPDH may have non-glycolytic functions. Moreover, Caspase-3 (Casp-3) expression increased with GAPDH silencing, suggesting alternative roles for GAPDH in apoptosis evasion.
