The effect of stocking density on growth, metabolism and ammonia–N excretion during larval ontogeny of the spiny lobster Sagmariasus verreauxi Mark A. Jensen a, ⁎, Quinn P. Fitzgibbon a , Chris G. Carter a , Louise R. Adams b a Institute for Marine and Antarctic Studies, Private Bag 49, Hobart, Tasmania 7001, Australia b National Centre for Marine Conservation and Resource Sustainability, Australian Maritime College, University of Tasmania, Locked Bag 1370 Launceston, Tasmania 7250, Australia abstract article info Article history: Received 23 August 2012 Received in revised form 26 October 2012 Accepted 28 October 2012 Available online 9 November 2012 Keywords: Energetics O:N ratio Ontogeny Oxygen consumption Phyllosoma Spiny lobster Stocking density is a critical factor affecting performance of aquatic organisms in culture, however, its influ- ence on energy utilisation has rarely been considered. Energy partitioning is particularly important for spiny lobster phyllosoma, which must accumulate sufficient energy reserves for metamorphosis and the non- feeding puerulus stage. The current study is the first to examine the energetics of spiny lobsters throughout the entire phyllosoma phase and determined the physiological influence of density. Growth and develop- ment, oxygen consumption and ammonia–N excretion rates were measured in Sagmariasus verreauxi phyllosoma that were cultured at High Density (HD) and Low Density (LD) from hatch to puerulus. Phyllosoma growth and development was more advanced in LD phyllosoma after 108 day in culture and mass of LD instar 17 phyllosoma was greater. There were no differences in routine metabolic rate (R r ) and ammonia–N excretion of phyllosoma between densities. However, the O:N ratio decreased in final instar phyllosoma demonstrating a shift towards higher protein catabolism. Routine metabolic rate also increased in late stage phyllosoma, possibly due to higher energy requirements in preparation for metamorphosis and increased swimming activity. The R r of spiny lobster larvae was significantly lower than that of other crustacean larvae, which may be a characteristic of their extended larval phase, slower growth rate, and larger body size. The study demonstrated late stage phyllosoma have higher weight specific energy require- ments than the preceding larval stages and exhibit a metabolic shift towards protein catabolism, suggesting an increased importance of storing lipid as an energy reserve for the puerulus stage. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction There is great interest in larval culture of spiny lobsters due to the high commercial value and apparent vulnerabilities of worldwide lobster fisheries (Jeffs, 2010; Jeffs and Hooker, 2000). Despite increasing consumer demand for lobsters, the development of commercial tech- nologies for the propagation of spiny lobsters has proved to be difficult. The evaluation of energy utilisation during larval development may indicate ontogenetic changes in growth efficiencies and reveal growth responses associated with specific culture conditions. However, to our knowledge the energetics of phyllosoma has not been examined throughout the entire larval phase. Stocking density is an important consideration in larval rearing because it may contribute to excessive expenditure of energy through increased physical interactions with prey and other phyllosoma and affect their ability to survive and successfully complete metamorphosis (Smith and Ritar, 2006). The influence of stocking density on energy partitioning is particularly important for phyllosoma as they must accumulate sufficient energy reserves for post-metamorphosis development as a lecithotrophic puerulus (Jeffs et al., 2002). Oxygen consumption rates (ṀO 2 ) represent overall aerobic me- tabolism, while ammonia–N excretion rates represent protein catab- olism (Ikeda et al., 2000). The most common measure in respiratory studies is arguably the routine metabolic rate (R r )(Cockcroft and Wooldridge, 1985), which ascertains how energy losses due to me- tabolism are influenced by environmental stressors (Lankin et al., 2008). Routine metabolic rate is defined as the intermediate state of metabolism measured in unfed animals displaying normal or sponta- neous activity and can vary considerably due to unquantified activity levels (Anger, 2001). An increase in metabolic rate induced by stress uses energy within the metabolic scope that could otherwise be utilised for other physiological functions, such as growth and devel- opment (Brett and Groves, 1979; Fry, 1971; Priede, 1985). High den- sities in aquaculture commonly induce considerable stress due to increased interactions with conspecifics and reduced water quality parameters (Sánchez et al., 2011). Stress associated with density may also affect O:N ratios as they are used to assess changes in energy substrate utilisation under various conditions (Corner and Cowey, 1968). According to the average elemental composition of the main compound classes, an atomic O:N ratio with a minimum value of 7 Aquaculture 376-379 (2013) 45–53 ⁎ Corresponding author. Tel.: +61 362277265; fax: +61 362278035. E-mail address: Mark.Jensen@utas.edu.au (M.A. Jensen). 0044-8486/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aquaculture.2012.10.033 Contents lists available at SciVerse ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aqua-online