Calcium influx and spermatogenesis in the testis and liver enzyme activities in the zebrafish are rapidly modulated by the calcium content of the water

This study investigated the effects of varying environmental Ca²⁺ concentrations on the influx of Ca²⁺ to the testis, testicular morphology, and liver enzymes in the zebrafish. Adult zebrafish (Danio rerio) were held in water containing low (0.02 mM), control (0. 7 mM) or high (2 mM) Ca²⁺ concentrations for 12 h. Testes were then incubated in vitro with 0.1 μCi/mL ⁴⁵Ca²⁺ to measure Ca²⁺ influx at 30 and 60 min and qualitative and quantitative testicular histological analyses were conducted. In addition, activity of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transpeptidase (GGT), enzymes that indicate tissue damage, were evaluated in the liver. The testes from zebrafish exposed in vivo to low (0.02 mM) and high (2 mM) Ca²⁺ content water had a higher Ca²⁺ influx than the control group after 30 min of incubation, and at 60 min (high Ca²⁺ group only). There were morphological changes in the testes from the low and high Ca²⁺ groups including spermatozoa distributed in dense agglomerates and apoptotic cells. Furthermore, zebrafish exposed to high Ca²⁺ containing water had an increased density of haploid cells (spermatids and spermatozoa). In addition, both low and high Ca²⁺ water affected liver function by increasing ALT and GGT activities. Collectively, these studies show that alterations in calcium homeostasis in the testis, stimulation of the spermatogenic wave and hepatic injury were rapid responses to changes in the concentration of Ca²⁺ in the water.