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In the study, we assessed how acute changes in water temperature and dissolved ammonia concentration can affect the swimming behavior pattern of rainbow trout (Oncorhynchus mykiss). The behavior was analyzed in three different stages: 1) increase stage, (where temperature and ammonia concentration increase during this step, respectively); 2) unchanged stage, (where levels of both factors do not change during this stage); 3) reduction stage, (where ammonia concentration and temperature during this stage are reduced), respectively. The results showed that both factors significantly changed the swimming pattern of the rainbow trout. There were significant differences in swimming parameters (distance from the center, swimming speed, total movement and the average of angular changes of movement) of treated fish in the comparison between treatments, and with the control group. The changes in the swimming pattern of fish in response to physicochemical parameters of water were confirmed to be a good tool in ecotoxicological studies., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Although we are witnesses of an increase in the number of studies examining the exposure/effects of microplastics (MPs) on different organisms, there are many unknowns. This review aims to: (i) analyze current studies devoted to investigating the exposure/effects of MPs on animals; (ii) provide some basic knowledge about different model organisms and experimental approaches used in studying MPs; and to (iii) convey directions for future studies. We have summarized data from 500 studies published from January 2011 to May 2020, about different aspects of model organisms (taxonomic group of organisms, type of ecosystem they inhabit, life-stage, sex, tissue and/or organ) and experimental design (laboratory/field, ingestion/bioaccumulation/effect). We also discuss and try to encourage investigation of some less studied organisms (terrestrial and freshwater species, among groups including Annelida, Nematoda, Echinodermata, Cnidaria, Rotifera, birds, amphibians, reptiles), and aspects of MP pollution (long-term field studies, comparative studies examining life stages, sexes, laboratory and field work). We hope that the information presented in this review will serve as a good starting point and will provide useful guidelines for researchers during the process of deciding on the model organism and study designs for investigating MPs., (Copyright © 2021 Elsevier B.V. All rights reserved.)

There is little information in scientific literature as to how conditions created by a microcystin (MC) producing cyanobacterial bloom affect the oxidant/antioxidant, biotransformation and neurotoxicity parameters in adult frogs in situ. We investigated biochemical parameters in the skin and muscle of Pelophylax kl. esculentus from Lake Ludaš (Serbia) by comparing frogs that live on the northern bloom side (BS) of the lake with those that inhabit the southern no-bloom side (NBS). A higher protein carbonylation level and lower antioxidant defense system capability in the skin of frogs living in conditions of the cyanobacterial bloom were observed. Inhibition of glutathione-dependent machinery was the major mechanism responsible for the induction of cyanobacterial bloom-mediated oxidative stress in frog skin. On the other hand, the detected higher ability of muscle to overcome bloom prooxidant toxicity was linked to a higher efficiency of the biotransformation system through glutathione-S-transferase activity and/or was the consequence of indirect exposure of the tissue to the bloom. Our results have also revealed that the cyanobacterial bloom conditions induced the cholinergic neurotransmitter system in both tissues. This study provides a better understanding of the ecotoxicological impact of the MC producing cyanobacterial bloom on frogs in situ. However, further investigations of the complex mechanism involved in cyanobacterial bloom toxicity in real environmental conditions are required., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Metals are involved in the formation of reactive oxygen species and can induce oxidative stress. The aim of this study was to assess the effects of several metals on oxidative stress in the skin and muscle of the Pelophylax esculentus "complex" frogs (parental species Pelophylax ridibundus, Pelophylax lessonae, and their hybrid Pelophylax esculentus) that inhabit the wetland Obedska Bara in Serbia, and the potential use of these species as bioindicator organisms in biomonitoring studies. The biomarkers of oxidative stress (SOD, CAT, GSH-Px, GR, GST activities and GSH, SH concentrations) and cholinesterase activity were investigated. The concentrations of nine metals (Fe, Cu, Zn, As, Cd, Cr, Hg, Ni, and Pb) were measured in the water and tissues. Correlations were established between metals and biomarkers in the tissues. The results of metal accumulation distinguished the skin of P. lessonae and muscle of P. ridibundus from other P. esculentus complex species. The oxidative stress biomarkers observed in P. ridibundus and P. esculentus had greater similarity than in P. lessonae. The P. lessonae displayed the highest number of correlations between biomarkers and metals. The results of tissue responses revealed that skin was more susceptible to metal-induced oxidative stress, with only exception of As. In the light of these findings, we can suggest the use of P. esculentus complex species as a biomonitoring species in studies of metal accumulation and metal-induced oxidative stress, but with special emphasis on P. lessonae.

Heavy metal pollution of the aquatic environment is of great concern worldwide. Heavy metals are capable of inducing oxidative stress by increasing the formation of reactive oxygen species (ROS), and directly affecting the antioxidant defense system (AOS) in living organisms. The frog Pelophylax kl. esculentus is a semiaquatic species with semipermeable skin and a complex lifecycle, and represents a potentially useful bioindicator organism. The aim of this study was to investigate the accumulation of several heavy metals (Cd, Co, Cr, Cu, Fe, Hg, Ni, Pb and Zn), and their effects on selected parameters of the AOS, including the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), phase II biotransformation enzyme glutathione-S-transferase (GST), the total glutathione (GSH) contents and sulfhydryl (SH) group concentrations, as well as cholinesterases (ChEs) activities in the liver, skin and muscle of P. kl. esculentus. Frog samples were collected at two sites (the Danube-Tisza-Danube canal (DTDC) and the river Ponjavica) in Serbia, which are characterized by different levels of metal pollution. Differences between the metal contents in different tissues showed that the skin of frogs from the DTDC accumulated statistically higher concentrations of Cd, Cu, Pb and Zn, while only the Fe concentration was lower. No significant differences between metal concentrations in muscle tissues of frogs from the DTDC and Ponjavica were observed. Examination of the parameters of the AOS revealed that frogs from the DTDC had higher concentrations of GSH in the liver and of SH groups in the skin and muscle, whereas the activities of the antioxidative enzymes SOD, GHS-Px and GR in the liver and of GR in the skin were lower than in frogs from the Ponjavica. The relationship between metal concentrations and AOS parameters showed the highest number of correlations with GSH, GR and CAT, and with Ni, Zn, Hg, Cr and Cd. Based on the results in this study, we concluded that increased concentrations of heavy metals in frog tissues can alter the AOS, which leads to higher concentrations of GSH and SH groups and lower activities of antioxidative enzymes. The response of the AOS to metal pollutants allowed us to make a distinction between different frog tissues, and to conclude that the liver and skin are more suitable for assessing metal-induced oxidative stress in frogs than muscle., (Copyright © 2016 Elsevier Inc. All rights reserved.)