Growth-dependent survival mechanisms during the early life of a temperate seabass (Lateolabrax japonicus): field test of the ‘growth–mortality’ hypothesis MD. SHAHIDUL ISLAM,* ,  MASAHIRO UENO AND YOH YAMASHITA Maizuru Fisheries Research Station, Field Science Education and Research Center, Kyoto University, Maizuru, Kyoto 625-0086, Japan ABSTRACT Three concepts based on size, time and growth rate are contained in the functional mechanisms of the ‘growth–mortality’ hypothesis, and are known as the ‘bigger is better’, ‘stage duration’ and ‘growth-selective predation’ hypotheses, respectively. Although it is sufficiently documented in fishes that faster growing and bigger larvae selectively survive, synergistic oper- ation of the three components of the ‘growth–mortal- ity’ hypothesis within a species have received little attention. In this study, we have tested the components of the ‘growth–mortality’ hypothesis based on the growth characteristics of original population (OP) and survivors (SV) of Japanese seabass (JSB) Lateolabrax japonicus. Larval and juvenile JSB were repeatedly sampled from the Tango Sea in 2007 and 2008. Oto- liths from larvae and juveniles were analyzed to pro- duce back-calculated daily records of size-at-age and growth rate, and were compared between OP and SV. Selective survival for fast-growing and bigger larvae was evident, and our results strongly support the ‘bigger is better’ hypothesis as well as the ‘growth-selective predation’ hypothesis. Growth rates of the individuals that metamorphosed into juveniles had significantly faster growth rates than non-metamorphosing larvae older than 48 days, the minimum age for metamor- phosis, suggesting a clear relationship between growth rates and the timing of metamorphosis. On average, SV completed the larval stage 13 days earlier than those of OP, supporting the ‘stage duration’ hypothesis. Thus, SV of JSB exhibited traits consistent with all aspects of the ‘growth–mortality’ hypothesis: faster growth, bigger size-at-age, and shorter larval stage duration (LSD), i.e., larvae with faster growth, bigger size-at-age and a shorter LSD selectively survived the larval period. Although maternal influence on growth and survival was evident, factors that regulate growth–mortality mechanisms remain to be explored for JSB. Key words: ‘bigger is better’, ‘growth–mortality’, hypothesis, Japanese seabass, larval stage duration, Lateolabrax japonicus, selective survival INTRODUCTION The early life stages of fishes generally experience high mortalities (Bailey and Houde, 1989; Houde, 1997) that are attributed to a variety of sources including predation, starvation, physical transport and sublethal factors (Anderson, 1988; Bailey and Houde, 1989; Leggett and DeBlois, 1994), although the relative role of each of them in overall mortality remains unre- solved. In understanding the mechanisms underlying demographic changes and recruitment dynamics of pelagic fishes, both biotic and abiotic factors have been examined and, subsequently, a variety of hypotheses have been proposed (Anderson, 1988; Cushing, 1990; Leggett and DeBlois, 1994). It is now believed that the high mortality experienced by mar- ine fish larvae does not always occur in a random fashion; rather, mortality is often growth- and size- dependent, preferentially removing slow-growing and smaller individuals from a cohort (Hovenkamp, 1992; Meekan and Fortier, 1996; Searcy and Sponaugle, 2001; Takahashi and Watanabe, 2004; Meekan et al., 2006; Shoji and Tanaka, 2006; Robert et al., 2007; Takasuka et al., 2007). Studies have suggested that even subtle variations in growth rate can lead to wide fluctuations in population size (Houde, 1989; Cam- pana, 1996); therefore, larval growth rates and body size may be useful predictors of recruitment success. *Correspondence. e-mail: dr.md.islam@gmail.com   Present address: Alfred Wegener Institute for Polar and Marine Research, Biologische Anstalt Helgoland, Postbox 180, 27483 Helgoland, Germany Received 18 June 2009 Revised version accepted 17 February 2010 FISHERIES OCEANOGRAPHY Fish. Oceanogr. 19:3, 230–242, 2010 230 doi:10.1111/j.1365-2419.2010.00539.x Ó 2010 Blackwell Publishing Ltd.