Growth of silver catfish (Rhamdia quelen ) exposed to acidic pH at different humic acid levels

Crescimento de jundiás (Rhamdia quelen) expostos ao pH ácido em diferentes níveis de ácido húmico

ABSTRACT:

Humic substances are organic compounds that possess high molecular weight and are formed by the decomposition of plant materials. Humic substances comprise humic acids, fulvic acids and humin. Humic acids (HA) have shown to be able to provide some protection to biological membranes of fish in water with low pH, replacing the protective action of Ca²⁺. Thus, this studyaimed to observe growth of silver catfish (Rhamdia quelen ) juveniles exposed to pHs 5.5 and 6.5 and to different levels of HA: 0, 10, 25 and 50mg L^-1. Results showed that, irrespective of pH, HA was highly detrimental to silver catfish growth, since the higher the concentration of HA, the lower the weight gain and feed intake, resulting in lower biomass and lower specific growth rate of juveniles. Hence, HA is extremely damaging to the performance of silver catfish juveniles in the tested concentrations.

Key words:
Humic substance; water pH; fish growth; organic carbon