The effects of stocking density on key biological parameters influencing culture productivity of the calanoid copepod, Parvocalanus crassirostris Fahad Alajmi ⁎, Chaoshu Zeng Centre for Sustainable Tropical Fisheries and Aquaculture, School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia abstract article info Article history: Received 10 May 2014 Received in revised form 11 August 2014 Accepted 16 August 2014 Available online 23 August 2014 Keywords: Copepod Parvocalanus crassirostris Stocking density Egg production Population growth Sex ratio Copepods are the most common metazoans in the marine environment and are considered to be ideal live prey for fish larvae. However, the difficulty in their culture, particularly at high culture density, hinders their use in aquaculture hatcheries. The aim of this study was to evaluate the effects of initial stocking density on a range of biological parameters affecting the culture productivity of the calanoid copepod Parvocalanus crassirostris. Five initial stocking densities of 1000, 3000, 5000, 7000 and 9000 adults L -1 were evaluated. Among the treatment differences on both daily and total egg production, the egg hatching rate and mortality rate were all highly significant (p b 0.001). Egg production was monitored over seven consecutive days, and the density of 5000 adults L -1 produced significantly (p b 0.001) more eggs daily than did the other treatments. Egg hatching success was very high at 91.8–92.3% at the lower initial stocking density of ≤5000 adults L -1 ; however, as density increased to ≥7000 adults L -1 , it dropped sharply to only 55–73%. Similarly, significantly higher adult mortality rates were recorded for densities ≥7000 adults L -1 . Moreover, population growth was evaluated for a 15-day culture period. It showed that the initial stocking density of 5000 adults L -1 produced the highest final population (6429.4 ± 202.2 individuals L -1 ) at the end of the culture period. However, in terms of percent- age population growth over the initial population, it was the lowest density of 1000 adults L -1 that achieved the highest growth (319.4 ± 20.0%), while high density treatments of 7000 and 9000 adults L -1 suffered negative percentage growth. Interestingly, the sex ratio was also significantly affected by initial stocking densities as the male to female ratio increased significantly at a density of ≥7000 adults L -1 . Our results demonstrated that P. crassirostris is a highly promising species for culture as live prey for aquaculture hatcheries, and it can be stocked at a high initial density of 5000 adults L -1 without negatively impacting culture productivity. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Copepods are the natural prey for the larvae of most marine fish in the wild (Østergaard et al., 2005; Sampey et al., 2007); however, to date, the use of copepods in commercial aquaculture hatcheries remains sporadic, which can be largely attributed to the fact that copepod pro- duction is still problematic and challenging (Drillet et al., 2011). Al- though rotifers had traditionally been used as live feed because of their convenience, rotifers are often found to be too large for the first larval feeding of various fish species and were also found to be nutri- tionally deficient (van der Meeren et al., 2008; VanderLugt et al., 2009). In contrast, the relatively smaller size of copepod nauplii is suit- able for the early larvae of most fish species (McKinnon et al., 2003). Their unique hop-and-sink swimming pattern also has the aptitude to elicit strong feeding responses in fish larvae (Bradley et al., 2013; Buskey et al., 1993; Støttrup and Norsker, 1997). Moreover, copepods are nutritionally superior, particularly considering that they contain high levels of long chain polyunsaturated fatty acids, which have been demonstrated to be vital for fish larvae (McKinnon et al., 2003; van der Meeren et al., 2008). In recent years, the failure of traditional live prey in the rearing lar- vae of various commercially valuable fish species, such as groupers (e.g., Epinephelus coioides) and snappers (e.g., Lutjanus campechanus), has generated renewed interest in developing intensive culture tech- niques for copepods as the alternative prey for the larvae of marine fish and crustaceans (Buttino et al., 2012; Payne and Rippingale, 2001; VanderLugt et al., 2009). As a result, successful intensive production of copepods has been reported for a number of species (Støttrup, 2006). As the most abundant copepod taxonomic group (Mauchline, 1998), calanoid copepods have been considered the most promising candi- dates for hatchery larval prey (Conceição et al., 2010; Evjemo et al., 2003). However, planktonic calanoid copepods are considerably more difficult to culture compared to benthic copepods (Støttrup, 2006). They typically demand a large water volume, robust management of water quality and a food supply of mainly live microalgae (Payne and Rippingale, 2001; Puello-Cruz et al., 2009). Despite increased research in recent years aimed at enhancing cope- pod culture techniques, the inability to achieve high culture density is still a major bottleneck in copepod culture, particularly for calanoid Aquaculture 434 (2014) 201–207 ⁎ Corresponding author. Tel.: +61 7 47816237; fax: +61 7 47814585. E-mail address: Fahadfshsh.alajmi@my.jcu.edu.au (F. Alajmi). http://dx.doi.org/10.1016/j.aquaculture.2014.08.029 0044-8486/© 2014 Elsevier B.V. All rights reserved. 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