The hadal zone (from 6 to 11 km depth) is one of the least explored habitats on Earth, and the knowledge about trophic ecology of hadal organisms is limited. Here, we analyzed fatty acid biomarker and stable isotope ratios of the amphipod species (Alicella gigantean) collected in the New Britain Trench (8225 m depth) in the southwestern Pacific Ocean. A total of 50 samples were divided into five developmental stages according to body length (1–129 cm): Stages I (juvenile), II (sub-adult) and III/IV/V (adult). Stages III, IV and V were further divided according to sex. Mean total fatty acid content for stage I (237.7 ± 105.6 mg g^-1) was significantly lower than that for stages II to V (476.4 ± 49.0 mg g^-1). The δ¹⁵N (14.7–18.4‰) positively correlated with the body length, whereas the EPA/DHA (C_20:5ω3/C_22:6ω3) ratio (0.09–0.51) negatively correlated with the body length. These results suggested an increase of trophic level with growth. Principal component analysis (PCA) separated major fatty acids into three clusters: (1) C_18:1ω9, C_16:1ω7, C_14:1ω5 (indicative of carrion-based diet); (2) C_14:0, C_15:0, isoC_15:0, C_16:0, C_17:0, isoC_17:0, anteisoC_17:0, C_18:1ω7, C_18:0, C_20:1ω9, and C_22:1ω9 (bacteria/zooplankton-based diet); and (3) C_20:4ω6, C_20:5ω3, C_22:6ω3 and C_22:5ω6 (benthic fauna/algae-based diet). The PCA result revealed that stage I-individuals consumed more bacteria/zooplankton debris, stages II to IV-individuals primarily preyed on carrion, while stage V-individuals had more diverse diet (benthic fauna/algae and carrion). Female amphipods had higher proportions of monounsaturated fatty acids, lower proportions of polyunsaturated fatty acids, and higher δ¹⁵N compared to male amphipods, suggesting that female individuals rely more on carrion from higher trophic organisms. This sex-related difference, however, diminished from stage III to V. Overall, our fatty acid and stable isotope data suggest an ontogenetic diet shift for hadal amphipods that may contribute to their success in the deepest ocean.

干旱带（深度从6到11 km）是地球上探索最少的栖息地之一，并且有关干旱生物的营养生态学的知识有限。在这里，我们分析了在西南太平洋的新不列颠海沟（8225 m深度）收集的两栖动物物种（Alicella gigantean）的脂肪酸生物标志物和稳定的同位素比率。根据体长（1-129厘米），总共有50个样品分为五个发育阶段：I（少年），II（亚成年）和III / IV / V（成年）。III，IV和V期根据性别进一步划分。第一阶段的平均总脂肪酸含量（237.7±105.6 mg g ^-1）明显低于第二阶段至第五阶段的平均总脂肪酸含量（476.4±49.0 mg g ^-1）。该δ ¹⁵N（14.7–18.4‰）与体长呈正相关，而EPA / DHA（C _20：5ω3 / C _22：6ω3）比（0.09–0.51）与体长呈负相关。这些结果表明营养水平随着生长而增加。主成分分析（PCA）将主要脂肪酸分为三类：（1）C _18：1ω9，C _16：1ω7，C _14：1ω5（表示基于腐肉的饮食）；（2）C _14：0，C _15：0，isoC _15：0，C _16：0，C _17：0，isoC _17：0，anteisoC _17：0，C _18：1ω7，C _18：0，C _{20 ：1ω9}，以及C _22：1ω9（以细菌/浮游动物为基础的饮食）；（3）C _20：4ω6，C _20：5ω3，C _22：6ω3和C _22：5ω6（基于底栖动物/藻类饮食）。PCA结果显示，I期个体食用更多的细菌/浮游动物残骸，II期至IV期个体主要捕食腐肉，而V期个体饮食更多样化（底栖动物/藻类和腐肉）。女端足了的单不饱和脂肪酸的比例较高，多不饱和脂肪酸的比例较低，而高δ ¹⁵N与雄性两栖动物相比，表明雌性个体更多地依赖来自高营养生物的腐肉。但是，这种与性别相关的差异已从III期降低到了V期。总体而言，我们的脂肪酸和稳定的同位素数据表明，短脚类双足纲动物的饮食发生了转变，这可能有助于它们在最深的海洋中获得成功。