THE CHRONIC EFFECTS OF THE HEAVY METALS ON REPRODUCTIVE SYSTEM AND FERTILITY OF POECILIA RETICULATA

Abstract

Purpose of the work. The study aims to research the impact of the heavy metals (Cu, Zn, Cd, and their mixtures) in concentrations that exceed the fish farming MPC by 20, 1.3, and 1.5 times, respectively, and are the background for some waters of the Prydniproviia region on the reproductive system and fertility of guppies (Poecilia reticulata). To determine histomorphological changes in the gonads under the chronic action of the heavy metals.

Methodology. Model experiments with the guppy were conducted for 92 days in aerated aquariums with a volume of 5 liters. Water pollution in experimental aquariums was simulated by adding substances to the final concentrations: copper 0.02 mg/dm³, cadmium 0.0075 mg/dm³, zinc 0.013 mg/dm³, and a mixture of heavy metals. The control aquarium was filled with dechlorinated tap water. At the end of the experiment, morphophysiological studies of the fish were conducted. Histological analysis of the gonads was carried out according to generally accepted methods. Photofixation of the histological preparations was done at a magnification of 400× using a SIGETA M3 CMOS 25000 digital camera connected to a Ulab XY-B2TLED microscope.

Scientific novelty. Given the lack of information on the chronic effects of metals and their mixtures on the reproductive system of fish, there is a need to conduct model experiments. Under conditions of chronic exposure to Cd, Cu, Zn ions, and their mixtures in concentrations exceeding the fishery MPC, several pathomorphological changes were detected in the gonads of the guppy. In particular, the destruction of the membranes of oocytes and the yolk sac, lipid vacuolization of the cytoplasm of egg cells, as well as disruption of the integrity of the membranes of testes, degradation of their structure, and expansion of the interstitial space were found. Taken together, these changes led to a reduction in fertility or a complete lack of birth rates.

Conclusions. Chronic exposure to heavy metal ions for 92 days has led to a significant decrease in the fertility of the experimental fish. A common pathology was disruption of the integrity of the membranes of oocytes and intense lipid vacuolization of the cytoplasm. In the testes, structural abnormalities, a decrease in the number of mature spermatozoa, and condensation of spermatids (under the influence of cadmium) were detected, which may be a consequence of delayed maturation.