Regulation of calcium transport in the early life stages of an ancient fish, Acipenser fulvescens.

The freshwater, cartilaginous lake sturgeon (Acipenser fulvescens) encounters its greatest calcium (Ca(2+)) demand in the early life stages. In this study we examined Ca(2+) regulation of lake sturgeon larvae reared at three levels of environmental [Ca(2+)]-0.1, 0.2, and 1.5 mmol L(-1)-from hatch until after the transition to exogenous feeding. Examination of skin, gill, and yolk sac with scanning electron microscopy (SEM) indicated that the density and surface area of mitochondria-rich cells (MRCs) varies over developmental time but that availability of environmental Ca(2+) affected only MRC density. SEM results also demonstrated that Ca(2+) transport is adjusted in localization over the course of development, with the transition to primarily branchial uptake occurring earlier in the highest environmental [Ca(2+)]. Net whole-animal Ca(2+) flux was primarily dependent on influx rate. The increase in whole-body Ca(2+) uptake following the transition to exogenous feeding was greatest in larval lake sturgeon acclimated to low environmental [Ca(2+)], and it suggests that intestinal absorption may supplement enhanced branchial uptake in Ca(2+)-limited fish.