Features of histological adaptation of Marbled crayfish Procambarus fallax f. virginalis (Decapoda) to the different concentration of cadmium ions in model experiment

The article shows the results of studies on the influence of cadmium ions on the histological structure of antennal gland cells of marbled crayfish Procambarus fallax f. virginalis Martin et al., 2010 (Decapoda). Due to the fact that marbled crayfish got into the reservoirs of the Dnipropetrovsk region in 2015, it was necessary to study the possibilities of its adaptation to environmental factors of reservoirs for further prediction of its distribution or even acclimatization under conditions of toxicological contamination of the ponds of the steppe Prydniprovya. We conducted a laboratory model experiments to study the mechanisms of adaptation of marbled crayfish Procambarus fallax f. virginalis. The effect of different concentrations of cadmium ions (0.01 mg/l, 2 MРC) on physiological state and histostructure of the excretory system of marbled crayfish was determined. The cells of the antennal gland of marbled crayfish in the control had a size of 166.08 ± 10.13 μm2. Glandulocytes had clear cells edges, pronounced structure of ducts, and a clear basal membrane. The cells had large nuclei with a cross-sectional area of 51.31±3.92 μm2. The nucleic membrane had clear edges, there were nucleoli in nuclei that were characterized by basophilia. That is, the structure of the antennal gland of marbled crayfish in control was normal for Decapods. The worst histological picture of antennal gland cells was observed in individuals exposed to cadmium ions. The structure of the excretory ducts of the green gland was broken, they had fuzzy boundaries, contained a large number of fragments of glandulocytes cytoplasm. In some cells there was a picnose of nuclei, as well as the output of a nucleolus beyond the nucleus which is the appearance of the micronucleus. This phenomenon is caused by the toxicological effects of cadmium. Compared with control, the glandulocytes of the antennal gland were 14.8 % smaller, their area of cross-section reached 141.44±7.60 μm2. The nuclei of the glandular cells were also significantly lower by 17.5 % than such in control, and their area reached 42.32±1.74 μm2. To study the influence of cadmium on the glandular cells of the green gland of marbled crayfish, the index of nuclear-cytoplasmic ratio (NCR) was used. The indicator of nuclear-cytoplasmic ratio allows estimating the level of metabolism and detecting the manifestation of compensatory reactions of the organism of experimental crayfish. The value of NCR in the trial and control did not differ statistically and amounted to 0.31 units. This indicates an interproportional reduction in both the cytoplasm of the cells of the green gland and their nuclei, caused by cadmium exposure. It was determined that under the influence of heavy metals the size of the glandular cells and their nuclei decreases, while the nuclear-cytoplasmic ratio remains the same, which is probably an adaptive reaction of the excretory system against the influence of heavy metal ions. Investigation of the histological structure of tissues and organs of marbled crayfish will allow the development of measures for the determination of biomarkers for the bioindication of the aquatic environment using freshwater crayfish. The results of such studies have an important fundamental and applied significance for understanding the mechanisms of adaptation of crustaceans to the conditions of toxicological burden on aquatic ecosystems.