Wachstum und

[Walter]

Growth and survival of silver catfish larvae,

Rhamdia quelen(Heptapteridae), at different calcium and magnesium concentrations

Lenise Vargas Flores da Silva, Jaqueline Ineu Golombieski and Bernardo Baldisserotto

Neotropical Ichthyology, 3(2):299-304, 2005

Abstract:

Since the relative ratios of Ca2+ and Mg2+ can vary greatly from one water body to another, and lime used for the increase of water hardness or pH can have different ratios of Ca2+ and Mg2+ in its composition, the objective of this study was to analyze the growth and survival of silver catfish, Rhamdia quelen, larvae at different calcium and magnesium concentrations. After fertilization, eggs were randomly divided into 4 treatments (three replicates per treatment) with different concentrations of Ca2+ and Mg2+ at hardness values of 70 mg.L-1 CaCO3 (mg.L-1 : 5.2 Ca2+ and 14.12 Mg2+; 13.11 Ca2+ and 7.11 Mg2+; 20.26 Ca2+ and 2.86 Mg2+; 24.95 Ca2+ and 0.95 Mg2+) and 150 mg.L-1 CaCO3 (mg.L-1 : 5.2 Ca2+ and 32.70 Mg2+; 28.63 Ca2+ and 16.44 Mg2+; 44.68 Ca2+and 6.44 Mg2+; 62.78 Ca2+ and 0.95 Mg2+). There was also another group exposed to water hardness of 20 mg.L-1 CaCO3 (Ca2+ 5.2 mg.L-1 and Mg2+ 0.95 mg.L-1) at both experiments. The post-hatch larvae were transferred to continuously aerated 40 L polyethylene aquaria (400 larvae/tank) containing the same water as used for incubation. Samples of larvae were collected on days 0, 7, 14, and 21, and the length, weight, and specific growth rate were determined for each collection. Survival and biomass were calculated on day 21. At water hardness of 70 mg.L-1 CaCO3, the best survival and growth of silver catfish larvae was observed at water with 20.26 mg.L-1 Ca2+ and 2.89 mg.L-1 Mg 2+, with similar results to the group exposed to water hardness of 20 mg.L-1 CaCO3. However, compared to the group exposed to water hardness of 20 mg.L-1 CaCO3, survival and growth were lower at 150 mg.L-1 CaCO3. Therefore, a hardness range of 20 to 70 mg.L-1 CaCO3 is recommended for silver catfish larviculture, but with 20.26 mg.L-1 Ca2+ and 2.89 mg.L-1 Mg 2+ at 70 mg.L-1 CaCO3. Water hardness of 150 mg.L-1 CaCO3 is not recommended for this species.

Anmerkung: 20 ppm CaCO3 entspricht etwa 1,1° dH, 150 ppm CaCO3 etwa 8,4° dH
Die Überlebensrate bei 20 und 70 ppm etwa gleich hoch, die Wachstumsrate bei 20 ppm besser...
Höhere Mg2+ Konzentrationen wirken sich im Vergleich zu höheren Ca2+ Konzentrationen negativ auf die Brut aus...

Seltsamerweise erwies sich pH 8 als der optimale pH Wert für die Jungfischaufzucht...

Geringe Wasserhärte und hoher pH Wert optimal für die Aufzucht von Rhamdia quelen...???
Interessante Arbeit - da gerade in letzter Zeit vermehrt genau gegenteilige Stimmen laut werden, weiches Wasser sei für die Zucht nicht so entscheidend wie saurer pH Wert.

Aber man kann natürlich nicht von einer Fischart auf alle schließen - und dass derartige Untersuchungen für viele (Aquarien)Fischarten gemacht werden, ist eher unwahrscheinlich.