QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by FLIK, G. Articles by WENDELAABONGA, S. E. Search for Related Content PubMed Articles by FLIK, G. Articles by WENDELAABONGA, S. E.

Journal of Experimental Biology 120,249-264 (1986)
Published by Company of Biologists 1986

Effects of Low Ambient Calcium Levels on Wholebody Ca²⁺ Flux Rates and Internal Calcium Pools in the Freshwater Cichlid Teleost, Oreochromis Mossambicus

GERT FLIK ¹, JAMES C. FENWICK ², ZVONIMIR KOLAR ³, NICOLE MAYER-GOSTAN ⁴, and SJOERD E. WENDELAABONGA ¹

¹ Department of Zoology II, University of Nijmegen Toernooiveld 25, 6525 ED Nijmegen, The Netherlands
² Department of Biology, University of Ottawa, Ottawa, Ontario, Canada KIN 6N5
³ Department of Radiochemistry, Interuniversity Reactor Institute, Mekelweg 15, 2629 JB Delft, The Netherlands
⁴ Laboratoire Jean Maetz, CEA Departement de Biologie, BP 68, F, 06230 Villefranche-sur-Mer, France

Calcium fluxes and internal calcium pools were measured in fed, rapidly growing, male tilapia, Oreochromis mossambicus, acclimated to 0.8 mmol l^-1 (FW) and 0.2mmoll^-1 (LFW) Ca²⁺. Plasma calcium levels were slightly and significantly higher in the LFW tilapia, but muscle calcium concentrations were independent of ambient Ca²⁺. At the time of the experiments, the LFW fish were growing and accumulated calcium, although the calcium content of their hard tissues was reduced. The LFW fish had higher Ca²⁺ influx and efflux rates than the FW fish. The increase in the influx of Ca²⁺ in LFW fish was, however, substantially greater than the increase in the efflux of Ca²⁺, giving these fish a more than four-fold increase in net Ca²⁺ influx from the water: for a 20-g tilapia net uptake rates of Ca²⁺ from the water were 390 and 1620 nmol Ca²⁺ h^-1 for FW- and LFW-adapted fish, respectively. These values were calculated to represent at least 69% of the total calcium accumulated by these growing fish. This indicates that even in low-calcium water, tilapia absorb a significant amount of their calcium requirement directly from the water.

The pool of readily exchangeable calcium in the bone of FW fish was estimated to be about 7 % of the total hard tissue calcium. In the fish acclimated to LFW, this percentage increased to about 15 % as total hard tissue mineralization decreased. This may indicate that tilapia can increase the mobility of their hard tissue calcium during periods of low calcium stress.

Key words: teleost, bidirectional Ca²⁺ fluxes, low ambient calcium, internal calcium stores

Accepted on October 1, 1985