www.nature.com/scientificreports OPEN Acute and sub‑chronic efects of copper on survival, respiratory metabolism, and metal accumulation in Cambaroides dauricus Jie Bao, Yuenan Xing, Chengcheng Feng, Shiyu Kou, Hongbo Jiang* & Xiaodong Li* Trace metal contamination in the aquatic ecosystem occurs worldwide: although copper is an essential trace metal, it is considered as a pollutant at certain levels in China. Freshwater crayfsh Cambaroides dauricus is a commercially important wild species in northeastern China, in which is an important heavy industry area. The population of C. dauricus was decreasing sharply due to the environmental pollution and human intervention over the past 20 years. However, nothing is known regarding the responses of this species to trace metal toxicants. This study aimed to determine the acute and chronic toxicity of Cu and its toxicological efects on respiratory metabolism, as well as Cu accumulation in C. dauricus. The acute (96 h) median lethal concentration (LC50) value of 32.5 mg/L was detected in C. dauricus. Then, acute (96 h; 8.24, 16.48 mg/L) and sub‑chronic (14 days; 2.06, 4.12 mg/L) exposure in Cu was investigated by estimating the oxygen consumption rate, ammonium excretion rate, and Cu accumulation. Both acute and sub-chronic Cu exposure induced an inhibition of the oxygen consumption rate and ammonium excretion rate, and thereby, an increased O:N ratio. The shift in O:N ratio indicated a metabolic substrate shift towards lipid and carbohydrate metabolism under Cu stress. Cu accumulation in the hepatopancreas and muscles throughout the study was found to be time-dependent and concentration-dependent. The maximum accumulation in the hepatopancreas and muscle were almost 31.6 folds of the control after 14 days’ exposure to 4.12 mg/L concentration. Based on the present work, we suggest that crayfsh be considered a potential bioindicator of environmental pollution in freshwater systems. The study provides basic information for further understanding of the toxicological responses of this species to trace metals. Trace metal contamination in aquatic ecosystems has begun to grow at an alarming rate and now constitutes a signifcant global problem1. As shown in the Report on the State of the Ecology and Environment in China2 and the Environmental quality bulletin of China’s coastal waters3, the high concentration trace metal pollution have been reported in coastal waters, rivers and estuaries, even in the underground water, due to the directly discharged industrial pollution sources, domestic pollution sources and comprehensive drain outlets. For exam- ple, copper (Cu) pollution is still the major pollution indicators in marine coastal water and many river systems, which has received considerable attention in China. Cu is a necessary trace element for the growth and development of all known organisms, including humans and other vertebrates; it mainly acts as a cofactor for various enzymes involved in protecting cells against destruc- tion by oxidation4. In crustaceans, copper is a natural component of hemocyanin, the respiratory pigment used in oxygen transport and also plays a role in the molting cycle and in the synthesis of metallothioneins 5. Owing to the human intervention and industrial activities, Cu discharged from metal mines, smelters, and municipal sew- age fnds its way into aquatic systems, leading to elevated concentrations in freshwater6. For example, the copper Key Laboratory of Livestock Infectious Diseases in Northeast China, Ministry of Education, Key Laboratory of Zoonosis, Shenyang Agricultural University, Shenyang 110866, China. *email: [email protected]; 2015500075@ syau.edu.cn SCIENTIFIC REPORTS | (2020) 10:16700 | https://doi.org/10.1038/s41598-020-73940-1 1 Vol.:(0123456789) www.nature.com/scientificreports/ Cu concentration (mg/L) Normal concentration 0 20 24 29 35 42 50 Measured concentration 0.01 19.63 23.37 28.10 33.73 39.67 45.8 % – 98.2 97.4 96.9 96.4 94.4 91.6 Table 1. Nominal and measured concentration (mean ± SE, n = 3) of Cu in test solutions. Cu concentration (mg/L) Exposure time (h) 0 20 24 29 35 42 50 LC50 (mg/L) 24 h 0 0 0 15 40 72 80 39.11 (35.99–42.87) 48 h 0 0 0 27 68 85 90 34.87 (30.23–39.99) 72 h 0 0 0 30 75 85 95 33.80 (29.69–38.24) 96 h 0 0 0 37 77 88 100 32.50 (29.66–35.57) Table 2. Accumulated mortality (%) of C. dauricus exposed to various Cu concentrations for 24, 48, 72, and 96 h and its medium lethal concentration (LC50 with 95% confdence limits) calculated by Probit analysis. concentration of surface water nearby the Dabaoshan Mine of Guangdong province reached up to 10.614 mg/ L7; the copper level of the rural domestic sewage in Dianchi of Yunnan province was fuctuating between 3.983 to 8.111 mg/L8, which were signifcantly higher than the national water quality standards of China. Moreover, copper sulfate that is traditionally used to control flamentous algae and phytoplankton and external parasites in aquaculture also contributes to the increasing concentration of Cu in aquatic ecosystems9,10. As excess Cu is non-biodegradable and persistent, the residue thereby accumulates in the food chain and causes toxicity to aquatic life, even harmful to the human. Te freshwater crayfsh, Cambaroides dauricus, belonging to Astacidea, Astacoidea, Cambaridae, is widely distributed in China, Russia, and North Korea, and is a commercially important wild species in northeast- ern China11. C. dauricus mainly inhabits in shallow waters such as rivers, lakes, and streams with abundant aquatic plants. However, the northeastern China is an important heavy industry area, the serious water pollu- tion, especially of heavy metal pollution, has resulted in the population of C. dauricus decreasing signifcantly to endangered species over the past 20 years. Although many techniques had been used to treat diferent types of these wastewater that are contaminated with heavy metals such as copper, the seriously damaged ecological environment still cannot be well remedy. Te survival aquatic animals in this area appear to exhibit extraordinary tolerance to various environmental contaminants. As far as we know, no research has been examined the efects of trace metals on this species. Te efects of acute and chronic Cu toxicity on crustaceans have been investigated in several studies. Many physiological alterations take place during the exposure period, including metabolic systems, which, in turn, are manifested as growth10,12. While the long-time exposure to sub-lethal levels of Cu in crustaceans can further impact their survival, behavior, and reproduction, and eventually change the population quantity 13–17. Respiration and excretion are the basic physiological activities associated with energy metabolism in animals 18. Tey were critical and sensitive indicators to evaluate the physiological responses of environmental conditions 19–21. Trace metals accumulated in the tissues of the aquatic animals can directly refect their physiological state. Terefore, the purpose of this investigation was to evaluate the efect of acute (96-h) and sub-lethal chronic (14-d) Cu exposure on respiratory metabolism (manifested in the oxygen consumption rate, OCR; ammonia excretion rate, AER; and O:N) and Cu accumulation in freshwater crayfsh, C. dauricus. Based on the acute median lethal concentration (LC50) values, respiratory metabolism and Cu accumulation were evaluated at concentrations equivalent to 25% (8.24 mg/L) and 50% (16.48 mg/L) LC50 for sub-lethal acute assays, and at 6.25% (2.06 mg/L) and 12.5% (4.12 mg/L) LC 50 for sub-lethal sub-chronic studies. Our data are benefcial to further understand the toxicological responses of C. dauricus to heavy metals like Cu. Results Cu concentration. Te measured dissolved Cu concentrations ranged from 91.6 to 98.2% and were close to the normal values (Table 1). Terefore, nominal concentrations of Cu were used for presentation and calculation of toxicity parameters in the tolerance experiments. Tolerance. Te percentage mortality of C. dauricus exposed to Cu in each 24-h interval is shown in Table 2. No mortalities were observed in the control. Te mortality increased with a corresponding increase in the toxi- cant concentration at each 24-h interval. Mortality rates of 100% were observed afer a 96-h exposure to concen- trations of 50 mg/L. Te 96-h LC50 value was 32.5 mg/L. Acute metabolic rate responses. Table 3 clearly reveals the inhibition efects on OCR and AER of C. dauricus caused by acute Cu exposure. Te OCR and AER of C. dauricus decreased signifcantly with increasing SCIENTIFIC REPORTS | (2020) 10:16700 | https://doi.org/10.1038/s41598-020-73940-1 2 Vol:.(1234567890) www.nature.com/scientificreports/ Exposure concentration (mg/L) Oxygen consumption rate (mg/g/h) Ammonia excretion rate (mg/g/h) O:N ration Control, 0 0.252 ± 0.018a 0.0209 ± 0.0009a 10.56 ± 0.57c b ab b 8.24 (25% 96 h LC50) 0.131 ± 0.004 (48.0%) 0.0069 ± 0.0004 (67.0%) 16.77 ± 1.21 b b a 16.48 (50% 96 h LC50) 0.130 ± 0.010 (48.4%) 0.0043 ± 0.0001 (79.4%) 27.01 ± 1.76 Table 3. Efect of acute Cu (96-h) exposure on oxygen consumption rate and ammonia excretion rate in C. dauricus (mean ± SE, n = 4). Te values in the parentheses represent percentage decrease over the control. Diferent letters above the bars indicate signifcant diferences (P < 0.05). exposure to diferent concentrations of Cu (P < 0.05), but there was no signifcant diference between two expo- sure concentrations for OCR (P > 0.05). Afer Cu exposure for 96-h, OCR declined by 48.0% at 8.24 mg/L and 48.4% at 16.48 mg/L, while for AER, it decreased by 67.0% and 79.4%, respectively.