Influence of water mineralization and dissolved main cations on survival, size and seismosensory characteristics of perch fry (Perca fluviatilis L.)

Within two months the growing of the perch fry Perca fluviatilis L. carried out in the aquarium experiment. Fertilized eggs of this fish species were taken from the spawning ground of a small and unpolluted natural reservoir and placed in laboratory conditions for subsequent incubation under different hydrochemical conditions. Experimental groups of perch were created in two replicates that developed under control conditions with a water salinity of 160 mg/l, under conditions of fresh water diluted to 100 mg/l, and under conditions with water whose salinity was increased relative to the control to 400 mg/l in three different ways - by adding calcium, magnesium or sodium chloride salts. Temperature, light, and oxygen conditions for growing fry in all groups were the same. The perch larvae were fed first with small natural zooplankton, then with artificially grown nauplia of Artemia; perch fry - with tubificid from vermiculture. The average survival rates of late larvae and early fry of perch in the second half of the experiment were maximal in the groups that developed under hydrochemical conditions with the addition of Na+ and Mg2+ (73% and 67%), and minimal in the groups that developed in the least mineralized water (46%). At the end of the experiment, the surviving fry from the groups affected by the increased content of sodium chloride had statistically significantly (p < 0.05) larger linear sizes than the fry from the control groups and groups that developed in the least mineralized water. Perch fry from the groups affected by increased concentrations of Ca2+ were characterized by a statistically significant (p < 0.05) smaller number of pores in the infraorbital and mandibular seismosensory canals of the head, compared with fry formed in conditions of least water mineralization and the minimal content of this main cation in it. Thus, salinity values and features of the ionic composition of fresh water can significantly affect the development of perch fry, which should be taken into account when breeding it in aquaculture.

Phytocenotic and hydrochemical conditions of the new localities of Aldrovanda vesiculosa (Droseraceae) in Chernihiv Polissya

Aldrovanda vesiculosa is a rare stenotopic species threatened due to destruction of its biotopes. Since the species is protected nationally and internationally, monitoring of its populations is required. Information on growth conditions of A. vesiculosa in three new localities recorded in 2019 and 2020 in lentic (standing water) reservoirs with muddy sediments in the Chernihiv Polissya region is provided. All populations were found in communities of the alliance Utricularion vulgaris. In the first locality (Snovsk, an artificial pond with an area 0.6 ha), the population of A. vesiculosa (projective cover of 10%) occupied an area of 0.5 m × 1.5 m within the shoreline community of the Spirodelo-Aldrovandetum vesiculosae association. In the second locality (Lake Perekop, area 7 ha, in the floodplain of the Desna River) the species was found in an area of 1.5 m2, with projective cover of 25%, also within the Spirodelo-Aldrovandetum vesiculosae communities. In the third locality (Lake Nizhniy Bolhach, floodplain of the Dnipro River), this species was found in an area of 0.5 m2 within the communities of the Lemno-Utricularietum vulgaris association, with projective cover of 3%. The comparison of hydrochemical conditions of biotopes in the found localities and hydrochemical indicators of habitats of this species in the Czech Republic and Poland was carried out. In the first and second localities, the hydrochemical indices are optimal for A. vesiculosa. In Lake Nizhniy Bolhach, some quantitative characteristics of the water chemical composition are beyond the ecological optimum for this species, in particular, exceeded values of hydrogen index (pH 7.0), hardness (12.1 mmol/L), concentrations of calcium (163.039 mg/L) and magnesium ions (49.025 mg/L), while organic carbon content (1214 mg/L) is reduced. A short-term existence of A. vesiculosa in this locality is predicted.