Effect of dietary calcium on growth and survival of silver catfish fingerlings, Rhamdia quelen (Heptapteridae), exposed to different water pH

The purpose of this study was to verify the effect of dietary Ca2+ on the growth and survival of silver catfish fingerlings (Rhamdia quelen) exposed to different water pH (5.5, 7.5 and 9.0). Silver catfish fingerlings were randomly placed in a thermoregulated water re-use system with twelve 250 L-tanks, two 1000 L-biofilters and a 2000 L-reservoir with a medium flow of 3.84 L min−1 tank. Stocking density was 0.16 fingerlings L−1. To prepare the treatment diets, the control diet (0.8 g kg−1 Ca2+) was supplemented with CaCO3 to yield experimental diets with 6.4, 9.5 and 23.9 g kg−1 Ca2+. There were three replicates/treatments. Survival was more than 93.9% in all treatments. Exposure of silver catfish fingerlings to alkaline or acid water reduced growth, and this effect was not ameliorated by dietary Ca2+ supplementation. Moreover, when fingerlings were maintained in water with pH 7.5, the best dietary Ca2+ range for silver catfish fingerling growth was 0.8–6.4 g kg−1.