Introduction
Nutrition shapes the individual physiological pathways at early stages, resulting in long-term effects on juvenile growth and physiological functions. Most of the marine species common in aquaculture production present an altricial larval stage, which are larvae that develop a functional stomach during metamorphosis. Therefore, before undergoing dramatic transformations to metamorphose into the juvenile stage, altricial larvae must capture and process exogenous food even though the digestive system may not be fully formed, resulting in a limited digestive capacity. Early life environmental interventions are looked as a promising way to improve gut maturation and digestive efficiency in fish in the short-term that could improve biological efficacy in the long-term. The perspective of applying this novel concept to aquaculture industry provides numerous advantages, since digestive capacity is considered key to fish resilience and quality.
The more sensitive period for nutritional modulation should be during embryo development; however, the lack of in ovo modulation techniques has been a bottleneck for the concept to be tested. This work presents an innovative in ovo nutritional modulating technique based on low-frequency ultrasounds (sonophoresis) to enhance the transport of compounds across the embryo membranes. An early stimulus with five different concentrations of a bioactive compound involved in gut maturation was applied in zebrafish embryos at 3.5 hours post-fertilization (hpf). At 22 days post-fertilization (dpf), growth performance, digestive enzyme activities and gut microbiota composition were analysed to evaluate the larval nutrition-induced metabolic plasticity and the effects on fish digestive efficiency.
The preliminary results showed that fish survival, total length and dry weight were affected by the bioactive compound supplementation (p>0.05). Impact of bioactive compounds supplementation on digestive enzymes and fish microbiota is under analysis.
The early stimulus with the bioactive compound during the embryonic stage was successful in producing larger larvae at the end of the experiment. Gaining insight into the physiological modifications shaped by an early supplementation of a gut promoter in marine fish larvae will provide one more piece to tackle the current aquaculture challenge.
Acknowledgments
The present study was supported by projects ALG-01-0145-FEDER-029151 "PROLAR - Early metabolic programming in fish through nutritional modulation", and UID/Multi/04326/2019 financed by the FCT (Portugal). Sofia Engrola acknowledge a FCT investigator grant (IF/00482/2014/CP1217/CT0005) funded by the European Social Fund, the Operational Programme Human Potential and FCT.