Growth of juvenile blacklip abalone ( Haliotis rubra) in aquaculture tanks: effects of density and ammonia

Abstract

Grow-out density is a key factor to consider in abalone mariculture. The growth of 30–50-mm Haliotis rubra was reduced at high density. About 1800 juveniles were individually tagged and reared for 5 months in 12 gravity-fed raceway tanks at high and low density. Their growth and distribution in the tanks was monitored monthly. Density was found to affect growth directly through competition for preferred shelter space and indirectly through the degradation of water quality. Initial size was negatively correlated to growth in the first month of the experiment. Ammonia in the water was directly correlated to the number of abalone present upstream. Ammonia was negatively correlated with growth after the effects of density and initial size were removed. Growth appeared to be significantly reduced by this level of chronic ammonia exposure, which is lower than the effective level reported previously (EC 5=0.004 mg FAN/l).