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Volume 11
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10.3390/fishes11010026
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Article

Ultrastructural, Osmoregulation, Physiological Metabolism, and Antioxidative Response of Red Tilapia (Oreochromis spp.) Under Acute Alkaline Stress

by
Endalew Alemu
1,2,3,†,
Wei Ye
1,2,†,
Jixiang Hua
1,
Lynda Djemaoun
1,4,
Siqi Lu
2,
Mohamed Fekri Badran
5,
Yalun Dong
2,
Rahma Halim Mahmoud Aboueleila
1,
Mustafa Hassan Lotfy Saleh
1,
Jun Qiang
1,2,* and
Yifan Tao
1,2,*
1
Wuxi Fisheries College, Nanjing Agricultural University, Wuxi 214081, China
2
Key Laboratory of Freshwater Fisheries and Germplasm Resources Utilization, Ministry of Agriculture and Rural Affairs, Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi 214081, China
3
Amhara Agricultural Research Institute, Bahir Dar Fishery and Other Aquatic Life Research Center, Bahir Dar P.O. Box 794, Ethiopia
4
National Laboratory for the Control and Analysis of Fishery and Aquaculture Products and Environmental Health, Bouismail 42004, Algeria
5
Aquatic Hatchery Production Department, Fish Farming and Technology Institute, Suez Canal University, Ismailia 41522, Egypt
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Fishes 2026, 11(1), 26; https://doi.org/10.3390/fishes11010026 (registering DOI)
Submission received: 21 November 2025 / Revised: 30 December 2025 / Accepted: 31 December 2025 / Published: 2 January 2026
(This article belongs to the Special Issue Tilapia Aquaculture: State-of-the-Art)
Versions Notes

Abstract

With increasing global demand for fishery products, saline-alkaline aquaculture has emerged as a potential solution. However, limited information exists regarding the tolerance and adaptability of red tilapia (Oreochromis spp.) to alkaline environments. This study evaluated the acute semi-lethal toxicity of alkaline water and its physiological effects on juvenile red tilapia (44.80 ± 1.09 g; 12.84 ± 1.02 cm). Fish were exposed to NaHCO3 for 96 h at five alkalinity levels (50, 55, 60, 65, and 70 mmol/L). Survival declined significantly with increasing alkalinity, and the 96 h LC50 was 60.66 mmol/L, indicating relatively high alkaline tolerance. Gill tissue and serum samples were collected at 0, 12, 24, 48, and 96 h under 50 mmol/L NaHCO3 and freshwater (control). Under prolonged alkaline exposure, gill structure exhibited marked alterations, with SLL and ILCMT progressively decreasing over time. Serum antioxidant responses were impaired, showing a sustained decline in SOD activity and a rise in MDA content, indicating the onset of oxidative stress. TAOC, CAT, and GSH-Px displayed a biphasic response, rising initially before declining with continued stress. TP and GLU levels remained largely stable throughout. Energy metabolism indices also shifted dynamically: TC showed a transient increase followed by a decrease, whereas TG and LDH initially declined before rising later in the exposure period. Stress-related markers, including cortisol, T3, ALP, and ACP, were notably elevated during the exposure. Additionally, serum ion concentrations (K+, Ca2+, Na+, Cl−) increased gradually over the 96 h period, reflecting progressive osmoregulatory disturbance under alkaline stress. Overall, this study shows that juvenile red tilapia (Oreochromis spp.) have high alkaline tolerance (96 h LC50 = 60.66 mmol/L NaHCO3), but exposure to alkaline water causes significant physiological stress, affecting gill structure, antioxidant defense, metabolism, and ion balance. These results offer valuable insights into their adaptability to saline-alkaline aquaculture.
Keywords: acute alkaline stress; blood serum; histology; physiological response acute alkaline stress; blood serum; histology; physiological response

Share and Cite

MDPI and ACS Style

Alemu, E.; Ye, W.; Hua, J.; Djemaoun, L.; Lu, S.; Badran, M.F.; Dong, Y.; Aboueleila, R.H.M.; Saleh, M.H.L.; Qiang, J.; et al. Ultrastructural, Osmoregulation, Physiological Metabolism, and Antioxidative Response of Red Tilapia (Oreochromis spp.) Under Acute Alkaline Stress. Fishes 2026, 11, 26. https://doi.org/10.3390/fishes11010026

AMA Style

Alemu E, Ye W, Hua J, Djemaoun L, Lu S, Badran MF, Dong Y, Aboueleila RHM, Saleh MHL, Qiang J, et al. Ultrastructural, Osmoregulation, Physiological Metabolism, and Antioxidative Response of Red Tilapia (Oreochromis spp.) Under Acute Alkaline Stress. Fishes. 2026; 11(1):26. https://doi.org/10.3390/fishes11010026

Chicago/Turabian Style

Alemu, Endalew, Wei Ye, Jixiang Hua, Lynda Djemaoun, Siqi Lu, Mohamed Fekri Badran, Yalun Dong, Rahma Halim Mahmoud Aboueleila, Mustafa Hassan Lotfy Saleh, Jun Qiang, and et al. 2026. "Ultrastructural, Osmoregulation, Physiological Metabolism, and Antioxidative Response of Red Tilapia (Oreochromis spp.) Under Acute Alkaline Stress" Fishes 11, no. 1: 26. https://doi.org/10.3390/fishes11010026

APA Style

Alemu, E., Ye, W., Hua, J., Djemaoun, L., Lu, S., Badran, M. F., Dong, Y., Aboueleila, R. H. M., Saleh, M. H. L., Qiang, J., & Tao, Y. (2026). Ultrastructural, Osmoregulation, Physiological Metabolism, and Antioxidative Response of Red Tilapia (Oreochromis spp.) Under Acute Alkaline Stress. Fishes, 11(1), 26. https://doi.org/10.3390/fishes11010026

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