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.