Introduction
Microplastics, defined as plastic particles ranging from 1 μm to 5 mm, originate from the fragmentation of larger plastics or from industrial sources such as cosmetics and synthetic textiles. These pollutants pose a serious threat to aquatic organisms, potentially affecting their growth, health, and welfare by causing physiological and behavioural disturbances (Santos et al., 2022). This study aims to evaluate the impact of microplastic exposure on energy balance, stress-related behaviours, and overall performance in a freshwater species.
Materials and methods
Twenty-four goldfish (Carassius auratus) were divided into two experimental groups (n=12/group): control group (no exposure to microplastics) and microplastics-exposed group (15 μm polystyrene microspheres, 0.5 mg/L). To maintain microplastic concentration, they were renewed every 24 hours, with a 50% water change over a 14-day period. Food intake, locomotor activity, body weight, and length were daily recorded. After one week of treatment, black-white and open-field preference tests were performed to assess anxiety-like behaviours. At the end of the 14-day exposure, oxygen consumption (MO2) was measured through 24 h. Lastly, fish were euthanized (MS222, 400 mg/L), and liver, intestine, gonads, perivisceral fat, and hypothalamus were collected. The expression of genes related to feeding regulation was analysed in gastrointestinal tissues and hypothalamus.
Results and discussion
Exposure to microplastics for 14 days significantly reduced both feed intake (Fig. 1a) and food anticipatory activity (FAA), measured during the 2 h preceding feeding time (Fig. 1b). These results suggest a potent anorexigenic effect of microplastics, consistent with previous studies in the same species following 28 days of exposure (Zhang et al., 2024). Our results demonstrate that such effects become noticeable after only 14 days of exposure and might be mediated by upregulation of anorexigenic-related genes alongside a downregulation of orexigenic neuropeptides in hypothalamus. Regarding energy expenditure, an increase in metabolic rate was observed (Fig. 1c), aligning with previous findings in black rockfish (Sebastes schlegelii; Yin et al., 2019).
Together, these findings may explain the observed decrease in both body weight gain and standard growth rate in the microplastics-exposed group (Figs. 2a–b), consistent with previous results in other fish species (Salerno et al., 2021). A significant decrease in the hepatosomatic index and a trend towards reduced perivisceral fat index were also observed (Figs. 2c–d); both organs play essential roles in goldfish energy storage.
Moreover, fish exposed to microplastics spent less time and made fewer entries into the aversive zones in the behavioural anxiety tests: i.e. open area in the open field test, (Figs. 3a-b), and the white area in the black-white preference test (Figs. 3c-d). This suggests that microplastics may contribute to heightened anxiety-like behaviour, which may be related to the elevated cortisol levels observed after microplastic exposure (Zhang et al., 2024).
In conclusion, short-term exposure to microplastics negatively affected feeding, growth performance, metabolic rate and emotional reactivity in goldfish. These findings highlight the detrimental physiological and behavioural effects of microplastics, compromising energy regulation and overall welfare in this species.
Acknowledgements
This work was supported by Spanish Ministry of Science and Innovation [PID2022-136288OB-C32 (MCIN/AEI//10.13039/501100011033)].
References
Salerno, M., Berlino, M., Mangano, M.C. & Sarà, G. 2021. Microplastics and the functional traits of fishes: A global meta-analysis. Global Change Biology, 27: 2645-2655.
Santos, D., Luzio, A., Félix, L., Bellas, J. & Monteiro, S.M. 2022. Oxidative stress, apoptosis and serotonergic system changes in zebrafish (Danio rerio) gills after long-term exposure to microplastics and copper. Comparative Biochemistry and Physiology Part - C: Toxicology and Pharmacology, 258: 109363.
Yin, L., Liu, H., Cui, H., Chen, B., Li, L. & Wu, F. 2019. Impacts of polystyrene microplastics on the behavior and metabolism in a marine demersal teleost, black rockfish (Sebastes schlegelii). Journal of Hazardous Materials, 380: 120861.
Zhang, W., Tian, D., Yu, Y., Tong, D., Zhou, W., Yu, Y., Lu, L., Li, W., Liu, G. & Shi, W. 2024. Micro/nanoplastics impair the feeding of goldfish by disrupting the complicated peripheral and central regulation of appetite. Science of the Total Environment, 946: 174112.