The effect of chemical cues on settlement of pearl oyster Pinctada fucata martensii (Dunker) larvae Xiujuan Yu a,b , Weihong He a , Ji-Dong Gu a,c , Maoxian He a , Yan Yan a,b, ⁎ a South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China b Marine Biology Research Station at Daya Bay, Key Laboratory of Marine Bio-resources Sustainable Utilization, LED, Chinese Academy of Sciences, China c Laboratory of Environmental Toxicology, Division of Microbiology, The University of Hong Kong, Pokfulam Road, Hong Kong Received 8 October 2007; received in revised form 25 January 2008; accepted 11 February 2008 Abstract The pearl oyster Pinctada fucata martensii is an important aquaculture species in South China Sea and has great commercial value in the pearl culture industry. As difficulties in the commercial culturing of molluscs are mainly associated with larval settlement and metamorphosis, it is important to find a routine, inexpensive and effective technique for the induction of synchronous settlement and metamorphosis of larvae. In the present study, the effects of 11 chemicals on inducing larval settlement of the P. fucata martensii were investigated in the laboratory. The larvae were exposed to the chemicals for 96 h. Among the chemicals tested, K + (10 and 20 mM), Ca 2+ (1 and 50 mM), γ-aminobutyric acid (10 - 4 M), 3- isobutyl-1-methylxanthine (10 - 4 M), choline (10 - 3 , 10 - 4 M), acetylcholine (10 - 4 M), and serotonin (10 - 3 , 10 - 4 , 10 - 5 M) induced high percentage of the larvae to settle without acute toxic effects, while Mg 2+ , NH 4 + , dopamine, and 3-(3,4-Dihydroxyphenyl)-L-alanine at all the tested concentrations were less effective. Serotonin of 10 - 4 M resulted in the highest settlement rate, but the chemical is expensive. K + was slightly less effective, but the chemical is much cheaper, therefore maybe more economical in the commercial production. © 2008 Elsevier B.V. All rights reserved. Keywords: Chemical cues; Settlement; Pearl oyster; Pinctada fucata martensii (Dunker); Larvae 1. Introduction Many sessile marine invertebrates produce larvae that must spend some period of growth and development in the plankton before settling and metamorphosing into their juvenile forms. Abundant literature has shown that settling marine invertebrate larvae are influenced by specific physical, chemical and biological cues derived from a variety of sources in the envi- ronment (e.g., Crisp, 1984; Pawlik, 1992; Hadfield and Paul, 2001). Such cues may come from the surfaces of substrata (Faimali et al., 2004), the microbial biofilms presented on the substrata (Maki et al., 1989; Keough and Raimondi, 1996), the presence of conspecific adult (Andrews et al., 2001; Zhao and Qian, 2002) or specific prey (Todd, 1985). Considerable experimental evidence suggests that the most influential cues appear to emanate from biological sources, and these appear to be chemical in nature (Pawlik and Hadfield, 1990). However, the exact nature of the chemical cues is still unknown in most cases (Hadfield and Paul, 2001; Swanson et al., 2004). Understanding the environmental factors that influence settlement and metamor- phosis of marine invertebrate larvae could lead to advancements in aquaculture, antifouling technologies, and better management of ecologically important ecosystems (Hadfield and Paul, 2001; Swanson et al., 2006). The pearl oyster Pinctada fucata martensii is an important aquaculture species in South China (Wu et al., 2003; He et al., 2005). It is similar to many benthic marine invertebrates having a planktonic larval stage in its life history. The fertilized eggs develop through cleavage, blastula, gastrula, trochophore, straight-hinged veliger, umbonal veliger and pediveliger larvae that are competent to settle and metamorphose (Jin, 1992; Zhao Available online at www.sciencedirect.com Aquaculture 277 (2008) 83 – 91 www.elsevier.com/locate/aqua-online ⁎ Corresponding author. South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China. Tel./fax: +86 20 89101515. E-mail address: yany@scsio.ac.cn (Y. Yan). 0044-8486/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2008.02.010