Relationship between prey utilization and growth variation in hatchery-reared Pacific bluefin tuna,Thunnus orientalis(Temminck et Schlegel), larvae estimated using nitrogen stable isotope analysis

Abstract

In mass culture of Pacific bluefin tuna Thunnus orientalis, a marked growth variation is observed after they start feeding at 6-7 mm in body length (BL) on yolk-sac larvae of other species, and the growth variation in tuna larvae is a factor leading to the prevalence of cannibalism. To examine the relationship between prey utilization and growth variation, nitrogen stable isotope ratios (d 15 N) of individual larvae were analysed. A prey switch experiment was conducted under two different feeding regimes: a group fed rotifers (rotifer fed group), and a group fed yolk-sac larvae of spangled emperor, Lethrinus nebulosus (fish fed group) from 15 days after hatching (6.87 mm BL). The fish fed group showed significantly higher growth than the rotifer fed group. Changes in the d 15 N of the fish fed group were expressed as an exponential model and showed different patterns from those of the rotifer fed group. The d 15 N of fastgrowing tuna larvae collected in an actual mass culture tank after the feeding of yolk-sac larvae was significantly higher than those of the slowgrowing larvae, indicating that slow glowing larvae depended largely on rotifers rather than the yolk-sac larvae.

Isotopic discrimination factors and nitrogen turnover rates in reared Atlantic bluefin tuna larvae (<em>Thunnus thynnus</em>): effects of maternal transmission

“…ABFT larvae are fast-growing, showing a rapid development of internal organs, including that of the digestive system (Miyashita et al 2001, Kaji 2003, Yúfera et al 2014. Considering the high nutritional requirements for developing fast developmental rates, some authors have suggested that the feeding shift from a planktivorous to a piscivorous diet is particularly important for survival in this species (Tanaka et al 2014, Reglero et al 2014.…”

“…SIA has proven to be a potential tool to study trophic ecology of wild-caught fish larvae (Laiz-Carrión et al 2011, Quintanilla et al 2015. But field research still needs experimental proof to understand the patterns of ontogenic-related feeding shifts and isotopic variations (Gamboa-Delgado et al 2008, Varela et al 2011, Tanaka et al 2014.…”

“…The few experimental studies based on hatchery-reared bluefin larvae address growth variability issues (Miyashita et al 2001, Reglero et al 2014, nutritional condition variability (Tanaka et al 2010) and prey-dependent larval growth variability using stable isotope analysis (SIA) as food tracers (Tanaka et al 2014).…”

“…An alternative approach to understanding early life trophodynamics of larvae without examining gut contents is to estimate the natural content of the stable isotopes of nitrogen and carbon. Stable isotopes can elucidate the feeding niches of a particular species, detect their ontogenetic trophic shifts (Pepin and Dower 2007, Laiz-Carrión et al 2013, Quintanilla et al 2015, estimate the relative diet breadth (Sweeting et al 2007a, 2007b, Tanaka et al 2014) and analyse migration patterns (Rooker et al 2007). This technique is increasingly being applied in the study of trophic food web dynamics of marine ecosystems (Bode et al 2007, Logan et al 2010, Costalago et al 2012, Quintanilla et al 2015.…”

Comparison of isotopic turnover dynamics in two different muscles of a coral reef fish during the settlement phase

“…Results of a feeding experiment on larvae of the Pacific blue fin tuna (Thunnus orientalis) showed that nitrogen values of fish approximated the isotopic composition of the food source after 20 days (Tanaka et al 2014). In other experiments on larvae of the catfish Clarias gariepinus and Ictalurus punctatus, results of isotopic compositions reached the "plateau" phase between 4 to 10 weeks, respectively (Enyidi et al 2013, Filbrun andCulver 2014).…”