Cadmium-induced toxicity can affect fish embryo development, ion homeostasis regulation, energy metabolism, maturation and growth, stress response, and immunity. However, studies on the toxic effects of cadmium exposure to aquatic animals, particularly olive flounder (Paralichthys olivaceus), are limited. In this study, juvenile P. olivaceus (mean length, 12.9 ± 1.3 cm; mean weight, 23.1 ± 3.2 g) was exposed to waterborne cadmium (0, 50, 100, 200, and 400 μg/L) for 10 d. Hematological parameters, including hematocrit value and hemoglobin level, in P. olivaceus were significantly decreased after waterborne cadmium exposure. Plasma components such as calcium, glucose, cholesterol, glutamic-oxaloacetic transaminase, and glutamic-pyruvic transaminase were significantly altered via cadmium exposure. The activities of antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione S-transferase, were significantly altered in P. olivaceus after cadmium exposure. Acetylcholinesterase activity was significantly inhibited upon waterborne cadmium exposure. Hepatic heat shock protein 70 was significantly upregulated in P. olivaceus after waterborne cadmium exposure. Therefore, waterborne cadmium at concentrations of >100 or 200 μg/L can induce physiological toxicity in P. olivaceus via changes in hematological parameters, antioxidant enzymes, neurotransmitters, and stress indicators.

This study aimed to determine the toxicity standard and potential risks and effects of polyamide (PA) exposure on neurotoxicity, stress indicators, and immune responses in juvenile crucian carp Carassius carassius. Numerous microplastics (MPs) exists within aquatic environments, leading to diverse detrimental impacts on aquatic organisms. The C. carassius (mean weight, 23.7 ± 1.6 g; mean length, 13.9 ± 1.4 cm) were exposed to PA concentrations of 0, 4, 8, 16, 32 and 64 mg/L for 2 weeks. Among the neurotransmitters, the acetylcholinesterase (AChE) activity in the liver, gill, and intestine of C. carassius was significantly inhibited by PA exposure. Stress indicators such as cortisol and heat shock protein 70 (HSP70) in the liver, gill, and intestine of C. carassius were significantly increased, while immune responses to lysozyme and immunoglobulin M (IgM) were significantly decreased. Our study demonstrates the toxic effects of MP exposure on crucian carp's neurotoxicity, stress indicators, and immune responses.

Cadmium (Cd) is a non-essential trace element that poses significant toxic effects on fish. This review focuses on hematological and plasma biochemical parameters as key indicators of fish health under Cd exposure. Hematological parameters, such as red blood cell (RBC) count, hemoglobin (Hb) concentration, and hematocrit (Ht), were selected for their critical role in oxygen transport and their sensitivity to Cd-induced disruptions, which often result in anemia and impaired oxygen delivery to tissues. Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) provide further insights into erythropoiesis and hemoglobin synthesis, both of which are essential for assessing Cd toxicity. Plasma biochemical parameters, including calcium, magnesium, glucose, cholesterol, total protein, and liver enzymes such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP), are crucial for understanding ionic balance, metabolic regulation, and organ function, especially in fish exposed to Cd. These biomarkers offer a comprehensive view of the physiological stress and organ damage caused by Cd toxicity. This review synthesizes literature findings on the toxic effects of Cd on these parameters. It also discusses potential mitigation strategies, including dietary supplementation with antioxidants and trace elements, to counteract the harmful effects of Cd exposure.

Chub mackerel, Scomber japonicus, is heavily farmed and harvested due to its demand as a high-quality protein source rich in fatty acids. However, the effects of environmental cues on sexual maturation of the fish remain understudied. We aim to elucidate the effect of light manipulation on the hormones related to reproduction and on the stress response in the species. Mackerel were exposed to different photoperiods (12 h light:12 h dark or 14 h light:10 h dark) and light wavelengths (provided by white fluorescent bulbs or green LEDs). Total RNA extracted from the brain was assayed with quantitative polymerase chain reaction (a powerful technique for advancing functional genomics) and blood plasma was analyzed via immunoassay using ELISA kits. The mRNA expression of gene-encoding gonadotropin-releasing hormone, gonadotropin hormone, follicle-stimulating hormone, and luteinizing hormone were significantly increased through the use of an extended photoperiod and green wavelength, which also increased testosterone and 17β-estradiol plasma levels. Plasma levels of cortisol and glucose, which are indicators of a stress response, were significantly decreased through green LED exposure. Our results indicate that environmental light conditions affect the production of pituitary and sex hormones, and reduce the stress response in S. japonicus.

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