The effects of water and bottom sediments from Lake Balkash (Central Asia) on early development of fish and amphibians
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1
Al-Farabi Kazakh National University, Kazakhstan
In recent years, one of the major reservoirs of the Republic of Kazakhstan - Lake Balkash is experiencing dramatic environmental problems: shallowing and high pollution by contaminants of various origin. Lake Balkash, having spawning grounds and large areas for mass fish feeding, is one of the reservoirs that form the basis of the fisheries industry in the republic. In addition, at the expense of the lake’s resources, drinking, domestic and industrial water supply is provided, which makes it necessary to control the ecological status of the reservoir. The main source of hydro resources (up to 80%) of Lake Balkash is the transboundary river Ile, 70% of which flows through the People's Republic of China. Environmental problems have arisen as a result of the intensification of agriculture and industry in both the PRC and Kazakhstan. Uncontrolled water intakes and wastewater discharges into the river from industrial enterprises and agricultural production transforms the conditions of reproduction and development of commercial fish living in the lake and background species of amphibians, which affects their ontogenesis, abundance, and life expectancy. Fish and amphibians are extremely sensitive to pollution of water and bottom sediments, since toxicants enter their bodies with water and swallowed food. In addition, the most important and vulnerable stage of their life cycle - embryogenesis - takes place in the water. Violations of embryogenesis lead to the appearance of defects and malformations that reduce the viability and survival of the species, because of which entire populations are depleted and die. Thus, the state of biodiversity of fish and amphibians reflects the ecological state of Lake Balkash. Therefore, the aim of the research was to study cyto- and embryotoxic effects of water and bottom sediments of Lake Balkash on commercial fish and amphibians, as a possible cause of a decrease in biological diversity.
The objects of the research were embryos and larvae and juveniles of commercial species of fish (asp Aspius aspius, roach Rutilus rutilus, rosy bitterling Rhodeus ocellatus) and background species of amphibians (marsh frog Rana ridibunda and green toad Bufo viridis). Biotesting of water and sediments of Lake Balkash according to guidelines for standard assays Zebrafish Embryo Toxicity Test (ZFET) and Frog Embryo Teratogenesis Assay-Xenopus (FETAX) modified for studied species was performed. Water and sediments for biotesting were collected from five sites in the southwestern part of Lake Balkash: Kunayev Bridge, Karaoi, Bakanas, Topar, and Kuigan. In addition, content of malon dialdehyde (MDA) and activity of superoxide dismutase (SOD) and catalase (CAT) of juvenile fish and amphibians caught in these sites were studied, too.
Laboratory experiments revealed adverse effects of water and sediments from Lake Balkash on early development of fish and amphibians, which was manifested by increased mortality and malformations occurrence. Biotesting of water on fish demonstrated the highest survival rate (83%) of embryos incubated in water from the site near Kunayev Bridge. Survival rate was lower by 1.4-fold, 1.9-fold, 2.2-fold and 1.1-fold in groups of embryos incubated in water from Bakanas, Topar, Kuigan, and Karaoi, respectively. Similar results were obtained when tested water from the sites on amphibians embryos. The highest survival rate was in the group incubated in water from the site near Kunayev Bridge (80%), and difference between the groups was analogous to that from biotesting experiments on fish. Survival rates in groups of fish incubated with bottom sediments added into water were alike in groups Kunayev Bridge, Topar, and Karaoi (77, 72 and 73%, respectively) and higher than in groups Bakanas and Kuigan (64 and 59%, respectively). Similar trend was observed in biotesting experiments on amphibians. In all biotesting studies there were different numbers of malformations, and most common included pericardial edema, abnormal development of the yolk body, curvature of the spine and the tip of the tail, embryo coagulation both before and after hatching from the chorion in fish and abdominal edema, gut uncoiling, axial curvature, malformations of eyes and mouth in amphibians.
The biochemical study revealed increased content of MDA in liver of juvenile fish and amphibians collected in the sites. At the same time, activity of the antioxidant enzymes SOD and CAT was depressed. These results show high oxidative stress in the liver of fish and amphibians, which can be an indicator of unfavorable conditions for development of water animals.
Thus, the results of the research demonstrated that water and bottom sediments of the Lake Balkash cause mortality and developmental disorders in fish and amphibians, which indicates adverse effects of pollution of the lake by anthropogenic activity and the need for measures to restore and preserve the lake's ecosystem.
Acknowledgements
This work was supported by the Ministry of Education and Science of the Republic of Kazakhstan under grant No. AP05132792.
Keywords:
embryotoxic effect,
Antioxidant Enzymes,
Malon dialdehyde,
fish,
Amphibians,
water and bottom sediments pollution
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Poster
Topic:
ECOLOGY AND LIFE CYCLES
Citation:
Sutuyeva
L,
Shalakhmetova
T and
Mamilov
N
(2019). The effects of water and bottom sediments from Lake Balkash (Central Asia) on early development of fish and amphibians.
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00017
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Received:
29 May 2019;
Published Online:
14 Aug 2019.
*
Correspondence:
Mx. Leila Sutuyeva, Al-Farabi Kazakh National University, Almaty, Kazakhstan, s_leila_aktau@mail.ru