Modulation of calcium balance in tilapia larvae (Oreochromis mossambicus) acclimated to low-calcium environments

This study examined how developing fish larvae regulate their Ca²⁺ balance for acclimation to low ambient Ca²⁺. Calcium balance in newly hatched larvae was examined individually. Developing larvae not only increased Ca²⁺ influx but also decreased Ca²⁺ efflux when they were acclimated to low-Ca²⁺ environments. After acclimation for 8 days, the influx and efflux of the low-Ca²⁺ (0.02 mM) group were about 106% and 43%, respectively, compared to those of the high-Ca²⁺ (1.0 mM) group. Sensitivity and response to low-Ca²⁺ environments are age-dependent. Upon acute exposure to low Ca²⁺, newly hatched (H0) larvae increased both Ca²⁺ influx (from 24% to 67% of high-Ca²⁺) and net uptake (from 5% to 69%) within 64 h, while 3-day-posthatching (H3) larvae managed to reach the levels of the control within 38 h. Declining Ca²⁺ efflux in H3 larvae occurred 14 h after exposure, much faster than those in H0 larvae (38 h). It is suggested that modulation of Ca²⁺-balance mechanisms in developing larvae is dependent upon the levels of Ca²⁺ in the larval body.