Incubation of silver catfish, Rhamdia quelen (Pimelodidae), eggs at different calcium and magnesium concentrations

L.V.F. Silva, J.I. Golombieski, B. Baldisserotto-2003
Aquaculture, 228(1-4): 279-287
Abstract:

Ca²⁺ and Mg²⁺ are important for ionic regulation of freshwater fish because both ions influence the permeability of biological membranes, preventing diffusive flow and high ionic loss to water. The objective of this study was to analyze the hatchery rate and post-hatch survival of silver catfish (Rhamdia quelen) eggs at different Ca²⁺ and Mg²⁺ concentrations. Eggs were incubated in continuously aerated 4-l polyethylene bottles (600 eggs/bottle) at 24 °C and randomly divided into five treatments (three replicates per treatment) with different concentrations of Ca²⁺ and Mg²⁺ at hardness values of 70 and 150 mg l^-1 CaCO₃. There were also two control groups with hardness of values 20 mg l^-1 CaCO₃. Dissolved oxygen, pH, temperature, total alkalinity and nonionized ammonia levels in water were always satisfactory for fish culture throughout the experiments. The increase of water hardness to 70 mg l^-1 CaCO₃ (all treatments) increased hatch rate, but the highest Ca²⁺ level reduced post-hatch survival. However, the eggs incubated at water hardness of 150 mg l^-1 CaCO₃ presented the lowest hatch rates and post-hatch survival values at higher Ca²⁺ concentrations. These results suggest that the increase of water hardness to 70 mg l^-1 CaCO₃ using either Ca²⁺ or Mg²⁺ improved hatch rate, but the increase of waterborne Ca⁺² above 20 mg l^-1, irrespective of water hardness, is not indicated for incubation of silver catfish eggs because it reduces post-hatch survival.

(Departamento de Fisiologia, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil, e-mail of B. Baldisserotto: bernardo@smail.ufsm.br)

home