Gene expression, growth and survival of European sea bass yolk-sac larvae (Dicentrarchus labrax) after PHB administration

The reliable production of marine fish larvae is one of the major bottlenecks in aquaculture due to high mortalities mainly caused by infectious diseases. To evaluate if the compound poly-ß-hydroxybutyrate (PHB) might be a suitable immunoprophylactic measure in fish larviculture, its capacity to improve immunity and performance in European sea bass (Dicentrarchus labrax) yolk-sac larvae was explored. Dietary PHB was applied from mouth opening onwards to stimulate the developing larval immune system at the earliest possible point in time. Larval survival, growth, microbiota composition, gene expression profiles and disease resistance were assessed. PHB administration improved larval survival and, furthermore, altered the larva-associated microbiota composition. The bacterial challenge test using pathogenic Vibrio anguillarum revealed that the larval disease resistance was not influenced by PHB. The expression profiles of 26 genes involved e.g. in the immune response showed that PHB affected the expression of the antimicrobial peptides ferritin (fer) and dicentracin (dic), however, the response to PHB was inconsistent and weaker than previously demonstrated for sea bass post-larvae. Hence, the present study highlights the need for more research focusing on the immunostimulation of different early developmental stages for gaining a more comprehensive picture and advancing a sustainable production of high quality fry.海水仔鱼的稳定规模化生产是水产养殖的核心瓶颈之一，其高死亡率主要源于传染性疾病。为评估聚-β-羟基丁酸酯（poly-ß-hydroxybutyrate, PHB）能否作为鱼类仔鱼培育领域的适宜免疫预防手段，本研究探究了其对欧洲海鲈（*Dicentrarchus labrax*）卵黄囊仔鱼免疫功能与生长性能的改善效果。实验自仔鱼开口期起投喂添加PHB的饲料，以期在最早时间点激活发育中的仔鱼免疫系统。本研究检测了仔鱼的存活率、生长指标、菌群组成、基因表达谱及抗病能力。结果显示，投喂PHB可提升仔鱼存活率，同时改变仔鱼相关菌群的组成。采用致病性鳗弧菌开展的细菌攻毒试验表明，PHB并未对仔鱼的抗病力产生显著影响。针对26个参与免疫应答等生物学过程的基因的表达谱分析显示，PHB可调控抗菌肽铁蛋白（fer）与海鲈抗菌肽（dic）的表达，但该调控效应并不稳定，且强度弱于此前针对海鲈稚鱼的相关研究结果。综上，本研究指出需针对不同早期发育阶段的免疫刺激展开更多研究，以形成更全面的认知，进而推动高品质鱼苗的可持续规模化生产。