Effect of low ambient mineral concentrations on the accumulation of calcium, magnesium and phosphorus by early life stages of the air-breathing armoured catfish Megalechis personata (Siluriformes : Callichthyidae)

The accumulation of calcium, magnesium and phosphorus Has measured during a n 8-week period in the early life stages of the air-breathing armoured catf ish Megalechis personata acclimated to low-mineral fresh water (0.073 mmol l(-1) calcium, 0.015 mmol l(-1) magnesium, <0.001 mmol l(-1) phosphate) and high-mineral fresh water (0.59 mmol l(-1) calcium, 1.94 mmol l(-1) magnesi um, <0.001 mmol l(-1) phosphate), The fish accumulated calcium twice as fas t and phosphorus 1.5 times as fast in low-mineral fresh water (LMF) as in h igh-mineral fresh water (HMF), while the rate of accumulation of magnesium did not differ in LMF and HMF. The difference in the rates of accumulation of calcium and phosphorus between LR IF and HMF was independent of the grow th performance (food intake) in LMF and HMF. The mineral content of young M . personata from natural swamps and rainforest creeks in Suriname followed the LMF accumulation curves. The transition from aquatic respiration to bim odal respiration in the third week after hatching did not affect rates of m ineral accumulation. The high rates of accumulation of calcium and magnesiu m of M. personata in LMF of 654 and 58 mu mol h(-1) kg(-1), respectively, e xceed the rates of uptake of calcium and magnesium of teleosts reported in the literature, The high rates of mineral accumulation in the early life st ages of M. personata reflect the exponential growth during the first 8 week s after hatching and the requirements of the juveniles while building their dermal armour, M. personata is well-adapted to neotropical fresh waters wi th an extremely low mineral content. The accumulation of calcium and phosph orus is discussed in relation to the function of the bony armour of M. pers onata.