Abstract:Infauna have developed physiological and behavioral strategies to cope with the stresses of sedimentary environments. Of the two, behavioral strategies are more important because they create microenvironments in the burrows which are essential for the survival of burrowing benthic animals. However, the few relevant published studies have not clarified the relationship between behavioral strategies and the microenvironment of benthic animal burrows. In the present study, we used a behavioral observation device to study the effects of temperature (15 ℃, 20 ℃, and 25 ℃) and body size [large size (2.2±0.2) g, medium size (1.5±0.2) g, and small size (0.7± 0.2) g] on the behavior of Perinereis aibuhitensis in the burrow. We also investigated the water exchange, nutrients, and dissolved oxygen in the burrow. The results showed that temperature had a significant effect on the radial undulating frequency of P. aibuhitensis (P＜0.05), which increased with increasing temperature. Further, body size had a significant effect on the axial crawling velocity of P. aibuhitensis (P＜0.05). The axial crawling velocity of large P. aibuhitensis decreased with increases in temperature, whereas the axial crawling velocity of medium and small P. aibuhitensis increased with increasing temperature. The temperature and body size had no significant effect on the radial undulating and axial crawling duration (P＞0.05); however, body size had significant effects on the pumping volume, pumping rate, and nutrient dissolving efficiency (P＜0.05). The pumping volume and nutrient dissolving efficiency increased with increases in body size. Moreover, the maximum pumping volume of P. aibuhitensis was 10.01 L/d in the group of large individuals and the maximum dissolution efficiency of phosphate, nitrite, ammonia nitrogen, and sulfide in the burrow were 109.80 μg/cm² /d, 6.02 μg/cm² /d, 60.56 μg/cm² /d, and 15.40 μg/cm² /d, respectively. Radial undulating motion is the main action in moving and pumping. The dissolved oxygen threshold of pumping behavior in P. aibuhitensis is consistent with optimality theory, which is designated the “optimal dissolved oxygen obtainment strategy” in this study. It showed an upward trend with increases in temperature and body size. This study showed that small P. aibuhitensis individuals moved more actively than large ones at high temperatures or under low dissolved oxygen levels, indicating that they might have a higher tolerance for these conditions. The large P. aibuhitensis individuals showed a superior ability for bioirrigation at high temperatures. It was likely that dissolved oxygen in the burrow was the key factor driving the initiation of pumping. The release of nutrients from sediment is an additional effect resulting from the polychaetes pumping water to get sufficient oxygen.

Abstract:The aim of the present study was to investigate sex differences in light color preference and the key role of aromatase in the conversion of testosterone (T) to estradiol (E2) in the regulation of this preference in a stream-dwelling fish, Acrossocheilus fasciatus. Six monochromatic lights were tested. The effects of reduced aromatase activity, via drug inhibition, on plasma sex hormone levels (T and E2) and the preferences between sexes were investigated. The results showed that female and male fish preferred red light (around 637 nm in wavelength) and yellow light (590 nm), respectively. However, they were repelled by blue light (465 nm), purple light (405 nm), and white light with blue spectrum (447 nm), while the preference for green light (518 nm) was not obvious. Feeding the fish an experimental diet containing the aromatase inhibitor, letrozole (LZ), over 10 days, resulted in a significant reduction in the aromatase activity level in the brain and gonadal tissues, as well as in the plasma E2 level, but no change in the plasma T level was observed. Surprisingly, LZ also caused an obvious change in the color preference of lighting; i.e., females preferred blue light and males preferred red light after treatment. However, no significant changes occurred in the levels of T and E2; nor were there any in the preferences, except for the decrease in aromatase activity levels in both the females and the males fed with another experimental feed containing LZ+E2. In conclusion, the sex differences in the color preference of lighting in these fish are most likely related to the sex differences in aromatase activity and estradiol levels, but not significantly related to the testosterone levels.

Abstract:The passive electrosense is a primitive sense in the sturgeon and paddlefish. These fishes can sense environments by detecting the weak electric fields of bioelectric and non-bioelectric origins. Nevertheless, the electrosensory function of sturgeon has always been controversial and, in the past year, has been poorly investigated. To quickly and non-invasively assess sturgeon electroreception, the behavioral responses of cultured Siberian sturgeons to underwater aluminum rods, insulated aluminum rods, and plastic rods were assessed using behavioral methods. The aluminum rod produces a weak corrosion electric field with an amplitude of 90 μV under water, whereas the insulated aluminum rod and plastic rod do not. There was no significant difference in the frequencies of rod circling for the aluminum rod, insulated aluminum rod, and plastic rod (P＞0.05). However, the sturgeon exhibited more snaps to the aluminum rod than the insulated aluminum rod and plastic rod (P＜0.01). The feeding preference intensity of the sturgeon for the aluminum rod was 2, while for the insulated aluminum rods and plastic rods it was 0.96 and 0.28, respectively. This indicates that the corrosion electric field underwater evoked a feeding response from the Siberian sturgeon. The electrosense of sturgeons may play a role in prey discrimination at the last stage of striking behavior in feeding. The results also indicate that the reaction to the corrosion electric field of metals can be used as a behavioral model to verify the electroreception in sturgeons; they also provide a new concept that may help in the conservation of sturgeons as a resource.

Abstract:Group living is a widespread social phenomenon in animals (e.g., insect swarms, fish shoals, bird flocks, and mammal herds), and their collective behavior is affected by various environmental factors. Intensive human activities, such as angling, have different effects on the group structure and function of the targeted fish shoals. To investigate the effects of angling stress on the collective behavior of cyprinid fish, healthy juvenile Qingbo (Spinibarbus sinensis) with similar body mass were selected as the experimental fish. Our study included two angling treatments (control and angling stress), with each treatment being performed on 18 fish shoals comprising six observers. The collective behavior of shoals subjected to the two treatments in an open water environment was initially videotaped for 15 min before the angling stress (day 0) and again after 14 days of angling stress. The fish in the angling stress group were fished daily for 14 days, whereas those in the control group were not subjected to angling stress. Our results revealed that angling stress can increase the swimming speed of Qingbo individuals and their total individual movement distance; however, it reduced the synchronization of speed. Additionally, angling stress was found to increase both the inter-individual distance and nearest neighbor distance of Qingbo. However, it had no significant effect on the group speed or percentage of time spent on movement in this fish species. Therefore, angling stress could lead to a decline in the group polarization of Qingbo. Furthermore, we detected a negative correlation between the nearest-neighbor distance and group polarization of Qingbo, and the intensity of this correlation was enhanced by angling stress. Our findings suggest that angling stress can reduce the coordination and cohesion of Qingbo shoals, which may have negative effects on information exchange and transmission during group movement. Moreover, in this fish species, the strength of the trade-off between group cohesion and coordination could be enhanced under angling stress.

Abstract:To explore the characteristics of energy metabolism in Macrobrachium rosenbergii and their relationship with locomotive abilities under salinity stress, an experiment with four salinity levels [0 (control), 4, 8, and 12] was conducted. Oxygen consumption rates, key energy metabolism enzyme activity levels in gills and muscles, and swimming and tail-flipping abilities were determined after 48 hours of salinity stress. The results showed that there were no significant differences in oxygen consumption rates as salinity increased from 0 to 4; however, the values were significantly higher in the 8 and 12 salinity groups when compared with those in the control group (0 salinity). There were no significant differences in the activity levels of hexokinase (HK), phosphofructokinase (PFK), and lactate dehydrogenase (LDH) in the gill among different salinity level groups. However, the activity levels of pyruvate dehydrogenase (PDH) and cytochrome c oxidase (COX) in the gill were significantly elevated as salinity increased from 0 to 8. Moreover, the activity levels of PDH and COX in the gill were positively correlated with oxygen consumption rates. The activity levels of HK, PFK, and LDH in pleopod and abdominal muscles did not change significantly when salinity increased from 0 to 8, but PDH and COX activity levels in pleopod and abdominal muscles significantly decreased under the same condition. Significant decreases in the activity levels of HK, PFK, LDH, PDH, and COX were observed as salinity increased from 0 to 12, either in pleopod or abdominal muscles. With regard to locomotion, swimming ability significantly decreased when salinity increased from 0 to 8; meanwhile, the same decrease for tail-flipping ability was observed at a salinity of 12. Swimming ability was positively correlated with PDH and COX activity levels of the pleopod muscles, whereas tail-flipping ability was positively correlated with the activity levels of HK, PFK, and LDH in abdominal muscles. Our findings indicate that as a response to salinity stress, M. rosenbergii increases its reliance on aerobic metabolism in the gill, as evidenced by the increase in oxygen intake. However, these physiological regulations reduce the enzyme activity levels associated with energy metabolism in muscles, resulting in observed decrease in swimming and tail-flipping abilities of M. rosenbergii.

Abstract:Chemical alarm cues (CACs) play an important role in fish predator-prey interactions. To explore the model and plasticity of chemical alarm communication of fish, and to test the niche hypothesis of the chemical alarm response in fish, adult Rhodeus ocellatus individuals were exposed to either predator treatment or no predator treatment for 8 months, using the common garden experiment. Subsequently, the behavioral responses of adult and juvenile R. ocellatus to different chemical cues within the environment (water control, juvenile and adult CACs of R. ocellatus, and the predatory cue of Channa argus) were measured under different predation contexts. The results showed that in the predator-free treatment group, chemical information had a significant effect on the changes in motionless time of adult R. ocellatus (P＜0.05) but had no significant effect on the changes in motionless time juvenile R. ocellatus (P＞0.05). There was a significant difference in the changes in motionless time in response to predatory cues between adult and juvenile R. ocellatus (P＜0.05). However, in the predator treatment group, the changes in motionless time for both the adult and juvenile R. ocellatus had a significant response to all risky cues, including the CACs of juvenile and adult R. ocellatus, and the predatory cue of C. argus (P＜0.05). There was no significant difference between adult and juvenile R. ocellatus in behavioral response to a given chemical cue (P＞0.05). These results confirm the hypothesis that chemical alarm communication in R. ocellatus is dependent on the environment and the chemical alarm response model of R. ocellatus, in predation contexts, supports the niche hypothesis of the chemical alarm response in fish.

Abstract:Fighting and cannibalism in crabs are key factors that limit their production and economic potential. Fighting between crabs is not only affected by biological factors, such as gender and size, but also closely associated with the environmental conditions in which they live. As a common environmental factor, dissolved oxygen significantly affects the physiological metabolism of animals, subsequently changing the fighting behavior of individuals. To study changes in fighting behavior and energy metabolism of the swimming crab (Portunus trituberculatus) under different dissolved oxygen conditions, we used an observation system for fighting behavior that was constructed in our laboratory. The fighting behavior of swimming crabs was quantified under different concentrations of dissolved oxygen [(2.5±0.5) mg/L, (4.5±0.5) mg/L, and (6.5±0.5) mg/L]. Changes in glycogen in the hepatopancreas, as well as changes in glucose and lactic acid in hemolymph, were measured. The main results revealed as following: (1) With a decrease in dissolved oxygen concentrations, the fighting duration of the swimming crabs was significantly reduced, with the minimum value observed in the 2.5 mg/L treatment group, which was significantly lower than that in the other treatment groups (P＜0.05). Meanwhile, the fighting intensity between individuals also continuously decreased. (2) The frequency of fighting incidents for the swimming crabs significantly decreased with the decrease in dissolved oxygen, and the frequency of contact behavior and non-contact behavior among the winners in the three treatment groups were significantly higher than those of the losers in the fighting process (P＜0.05). (3) With the decrease in dissolved oxygen concentration, the levels of glucose and lactic acid in the hemolymph of the swimming crabs were significantly increased, and the level of liver glycogen was significantly decreased (P＜0.05). (4) After fighting, the liver glycogen level of the swimming crabs significantly decreased, whereas within the hemolymph, the glucose level significantly increased and the lactic acid level was significantly higher than what it was before fights (P＜0.05). The experimental results showed that the intensity of anaerobic respiration, energy supply efficiency, and lactic acid accumulation of swimming crabs were increased under hypoxia stress, which resulted in the decrease in fighting willingness and fighting intensity of the swimming crabs. Therefore, differences in energy metabolism may be one of the physiological mechanisms leading to differences in fighting behaviors under stress.

Abstract:This study outlines the effects of hypoxia stress on the behavior, physiology, immunity function, and key respiratory enzymes of Patinopecten yessoensis. To accomplish this, four dissolved oxygen (DO) gradients [1 mg/L, 2 mg/L, 4 mg/L, and 7 mg/L (control group)] were set to determine the behavioral characteristics (the degree of opening and closing of the shell), oxygen consumption rate, ammonia excretion rate, and the activity levels of antioxidant enzymes (SOD, CAT) and respiratory enzymes (LDH and PK). The results were as follows: (1) The survival rate of Patinopecten yessoensis decreased with the decrease in DO concentration; when DO was 1.0 mg/L, the survival rate was only 55%. At 1 mg/L, 2.0 mg/L, and 4.0 mg/L dissolved oxygen concentration, the median lethal time of the scallops was LT50=95.97 h, LT50=147.37 h, and LT50=209.58 h, respectively. (2) The behavioral characteristics of the scallops were divided into five grades numbered from 0 to 4; the higher the score, the better the scallop’s state. From the quantitative indicators of scallop behavioral characteristics, the lower the concentration of DO, the lower the score and the worse the state of the scallops. (3) Hypoxic stress had significant effects on the oxygen consumption rate and ammonia excretion rate of the scallops (P＜0.05) under the stress of DO≤2 mg/L. When the molar ratio of oxygen to nitrogen was ＜7, the energy supply of the scallops was mainly protein; whereas when the DO was ≥4 mg/L, the scallops were mainly sustained by protein and fat oxidation. (4) Hypoxia stress significantly affected the level of SOD, CAT, and respiratory enzymes (P＜0.05) in Yesso scallops. Being under 24-h hypoxia stress increased the concentration of reactive oxygen species (ROS) in the hepatopancreas and adductor muscle. After 48–96 h of hypoxia stress, the activity levels of the SOD and CAT enzyme began to decrease. The metabolic pathways are different under different concentrations of dissolved oxygen. The study has found that when DO=2 mg/L, the metabolism associated with aerobic respiration is converted to the glucose-pyruvate-lactic acid respiratory pathway and when DO=1 mg/L, the respiratory metabolic pathway may give priority to the glucose-succinate acid pathway. On physiological and biochemical levels, the decrease in immune function and the change in respiratory metabolic pathways may cause the changes in scallop behavior.

Abstract:To explore the effects of variations in dissolved oxygen concentrations on the feeding and metabolism of the mussel Mytilus coruscus and analyze the relationship between shell opening behavior and respiratory metabolism, we observed and measured the shell valve opening degree and rates of filtration, oxygen consumption, and ammonia excretion of M. coruscus exposed to 8, 6, 4, 2, and 1 mg/L dissolved oxygen and calculated the O:N ratio. The results revealed the following: at oxygen concentrations greater than 4 mg/L, the shell valve of M. coruscus mainly remained opened but gradually closed when the oxygen concentration decreased to below 2 mg/L; when the oxygen concentration decreased to 4 mg/L, the filtration rate decreased significantly; and the oxygen consumption remained stable when the oxygen concentration was between 2 and 8 mg/L but declined significantly when the concentration decreased to 1 mg/L. The ammonia excretion rate showed an opposite tendency, increasing significantly when the oxygen concentration decreased to 2 mg/L, and the O:N ratio significantly decreased when the oxygen concentration decreased to 4 mg/L. Furthermore, a positive relationship was found between the shell valve opening degree and the rates of filtration and oxygen consumption. The findings of this study indicate that M. coruscus can adapt to fluctuations in dissolved oxygen concentrations within a certain range and maintain a relatively stable metabolic level. However, in environments where dissolved oxygen concentrations decrease to below 1 mg/L, these mussels are unable to maintain normal metabolism and respond to hypoxic stress by closing the shell valve to reduce energy consumption. These observations can provide a reference for investigating the hypoxia adaptive mechanism and farming of M. coruscus.

Abstract:Green turtles (Chelonia mydas) are widely distributed in tropical and subtropical seas. As a typical long-distant migratory species, they frequently travel between feeding and nesting grounds, and some can travel thousands of kilometers in migrations. The green turtle population has sharply declined globally, chiefly due to overfishing and habitat loss. In addition, global warming can influence the population structure to a female-biased sex ratio. In this study, we designed the species distribution model (SDM) to predict the migration route and the potential distribution range of green turtles. The occurrence of green turtles and environmental variables were used to construct an ensemble SDM. Based on this model, the distribution range and possible migration route of the green turtle were projected under the conditions of future climate change scenarios. It was predicted that offshore distance, depth, and surface temperature will be important factors influencing the migration of green turtles. It was also predicted that the Western Pacific, Northern Indian, and Western Atlantic oceans will be important habitats. Migration corridors are found in Atlantic-Mediterranean and Indian-Pacific groups. In keeping with future climate change, the suitable habitats for green turtles under the low-concentration emission scenario (RCP26) will decrease, and the suitable habitats under the high-concentration emission scenario (RPC85) will increase, irrespective of the scenarios. Additionally, the green turtles showed a tendency to expand toward the polar regions under both two concentration emission scenarios. These results provide scientific methods to use in the protection of green turtles, an important marine species, by exploring possible migration routes and changes in their habitats under future climate change conditions.

Abstract:Personality refers to consistent individual differences in behavior over time and across contexts. At the population or species level, there exists a behavioral syndrome, wherein individuals display a certain behavioral type. Currently, behavioral syndromes in fishes are reviewed with respect to five main axes of animal personality: (1) shyness–boldness, (2) exploration–avoidance, (3) activity, (4) aggressiveness, and (5) sociability. Personality affects the behavioral performance and fitness of fish and has notable consequences with respect to the welfare of fish, stock enhancement, fishery management, and conservation. This review summarizes the current progress in fish personality research and provides an overview of its application in stock enhancement, information transmission, disease prevention and control, fishery resource management and protection, and biological invasion prevention and control. This review aims to provide fundamental information for future research and the applications of fish personality.

Abstract:Baited remote underwater video (BRUV) technology is a monitoring technique used to record the relative abundance and behavior of fish species. The benefits of using BRUVs have been well documented, including their non-destructive nature, replicability, and suitability for various habitat types and water depths. However, although BRUVs have been extensively used worldwide for over 20 years, no such studies have been undertaken in China. Here, we reviewed 278 scientific documents relating to BRUVs published between January 2006 and March 2020. For BRUV surveys in China, we recommend that BRUVs should use (i) a forward-facing camera to maximize the field of view; (ii) lightweight and easy to use GoPro cameras, which are suitable for shallow, well-lit waters (＜40 m deep); and (iii) oily fish such as clupeids (sardines and pilchards) as bait to attract carnivorous fish. Prior to using BRUVs, pilot studies should be conducted to quantitatively determine (e.g., using accumulation curves) the necessary deployment time. Generally, a running period of 60 min is sufficient for benthic BRUVs, although this would differ depending on the location. In terms of monitoring, the maximum number of observed individuals of a species in a single video frame (MaxN) is a widely accepted metric characterizing the relative abundance of species.