Optimizing the concentration of gamma-aminobutyric acid (GABA) for inducing larval metamorphosis in the red abalone Haliotis rufescens (Mollusca: Gastropoda)

Abstract

The induction of larval metamorphosis is a critical step in abalone Haliotis spp. culture. Recently, gamma-aminobutyric acid (GABA) has been used as an inducer by an increasing number of commercial hatcheries, because of its higher efficiency over other settlement methods. The conventional GABA concentration used is 1.0 micromolar as suggested by controlled laboratory experiments. However, poor results are occasionally reported in hatcheries, probably because the bacterial load in commercial systems degrade the inducer to levels below the required threshold. To cope with this problem, GABA concentration might be increased within safe limits to compensate for potential bacterial degradation, but information to adequately support this alternative is missing. This contribution describes two experiments on this issue with red abalone. H. rufescens larvae which suggest that GABA concentration could be increased at least 100% without causing the detrimental effects on metamorphosis induction or postlarval fitness reported for higher toxic levels. The impact of this result on abalone seed production is discussed.