Wang and Heino: Growth and maturation of Trichiurus japonicus in the subtropical Pacific Ocean 
179 
corresponding sex- and area-specific growth data at 
ages 1 and 2 revealed some phenotypic differences in 
maturation between the areas. As Figure 5 shows, the 
earliest maturation occurs in Tsukuan males (SW). In 
agreement with this observation, the males in Tsukuan 
have a relatively low PMRN midpoint, together with 
relatively large lengths for immature fish at age 1 (see 
Fig. 3A), resulting in a relatively high likelihood of 
maturation at that age. In contrast, for males in Keng- 
fang (NE), the PMRN midpoint for age 1 was greater 
than the lengths of most age-1 individuals, resulting in 
a greater tendency to have delayed maturation to age 2 
(Fig. 5, Fig. 6A). For female fish, between-area differ¬ 
ences in the midpoints of PMRNs were so small (Fig. 6) 
that the difference in length of immature fish did not 
result in clear differences in maturation. 
Discussion 
Our study provides evidence of variation in growth and 
maturation patterns and potential underlying driv¬ 
ers of those patterns for a subtropical cutlassfish at a 
small spatial scale. We found that growth rates of the 
early stage of juvenile T. japonicus (first few months) 
were similar between areas, whereas immature fish at 
ages of 0-1 years grew faster in the warmer Tsukuan 
(SW), corresponding to the spatial gradient of tempera¬ 
tures. However, results for growth of adults indicate an 
inverse pattern and that both adult males and females 
tended to be larger in the colder Kengfang (NE). Fur¬ 
ther, we found that T. japonicus generally matured at 
ages 1-2 in both areas, but males in Kengfang had a 
tendency for delayed maturation. Because the midpoints 
of PMRNs did not differ significantly between the ar¬ 
eas, growth-related phenotypic plasticity is sufficient to 
explain the observed variation in maturation schedules 
of males. This result contrasts with those from some 
earlier studies in which neighboring stocks or stock 
components were compared (marine fish: Olsen et al., 
2005; Vainikka et al., 2009; Wright et al., 2011; Mollet 
et al., 2013; freshwater fish: Wang et al., 2008; Morita 
et al., 2009). Overall, these observed patterns of differ¬ 
ences in growth and maturation between the areas are 
consistent with the temperature-size rule (Angilletta et 
al., 2004; Arendt, 2011), where cooler temperatures led 
to slower prematuration growth, delayed maturation, 
and larger asymptotic lengths for fish. However, with 
the comparison of only 2 fishing grounds and limited 
environmental data, we cannot exclude other sources 
that could produce plastic variation. 
Temperature-size rule involves thermal effects on growth 
and maturation 
A negative effect of temperature on adult body size, 
the temperature-size rule has been reported for vari¬ 
ous organisms (Atkinson, 1994; Angilletta et al., 2004). 
Such an effect of temperature on variation in body 
size may involve multiple plastic or adaptive pathways 
(Angilletta et al., 2004; Ohlberger, 2013). For example, 
temperature may induce plastic changes in physiologi¬ 
cal rates, such as growth, metabolism, and mortality 
and lead to the observed variation in body size (e.g., 
Munch and Salinas, 2009). Simultaneously, tempera¬ 
ture effects on the metabolic rates may induce adaptive 
changes. As metabolic costs increase with temperature, 
a thermal constraint on maximum body size may oc- 
