Juvenile fish are subject to numerous events in aquaculture operations: transportations, transfers, gradings, diverse handlings, various infectious pressures, water quality variations, first complete feed ingestion, mixing of populations, new environments and rearing structures, vaccinations,… All these events represent important stressful moments that may severely impact their health, immediately and on the long term, subsequently hampering their physiology and future growth performance.
At the same time, situated between hatchery and grow-out stages, nursery phase represents a crucial intermediary phase with fundamental physiological evolutions including morphological, immunological, and digestive features and capacities. Such changes have been described on Tilapia by Fujimara et al. in 2007.
Joining both external challenges and ontogenetic evolution is paramount in building a program to optimize the organism readiness to present and future challenges, thus performance. ADM1 has focused on this subject and developed Life Defense, a state of the art approach in order to better accompany fishes in these phases. This comprises both specific nutritional requirements at the considered physiological stage, as well as the help brought by selected feed ingredients that facilitate and promote particular physiological functions.
As first line defense, mucus is of capital importance in aquatic species. Salinas in 2015 reviewed its immunological roles at the skin, gut, and gills. More than just a physical barrier, mucus displays dynamic defensive interaction with its environment, including innate immunity such as antimicrobial peptides secretion and entrapment of microbes, as well as acquired immunity on specific targets.
Selection of effective immune modulators that allow for fast and reactive response and reducing long-term inflammation will decrease its vicious circle and favor fish recovery and resume to performance. Moreover, Peisker et al. in 2017 demonstrated the structural characteristics advantages of Pichia guilliermondii2 yeast on bacterial aggregation properties compared to other yeasts, while further studies showed three times faster Vibrio clearance from infected innate immune shrimp hemolymph.
Beyond its primary function in digestion, the intestine plays a fundamental role in immunity, both activities being closely related via its microbiota. Strategies involving weak and strong organic acids, or fostering firmicutes populations while reducing proteobacteria, allow to stabilize the gut microbiota and optimize its activities to promote performance and health.
Gut Microbiota populations under different treatments
Numerous plant extracts have proven biological activities, among which certain may be of particular interest when it comes to digestive epithelium protection, anti-oxidative activity, or decreased parasitic prevalence associated with their inclusion in feed (Fridman et al., 2014).
In conclusion, special attention and caring during this critical life stage that is nursery, on nutritional needs but also on challenges met during this period, provide return on the investment. Conversely, skipping or neglecting it often leads to laborious and continuous farm management hazards including disease outbreaks, compromising farm economics and sustainability. As mentioned by Valente et al. in 2013, successful nursery is a key target for a competitive expansion of the aquaculture industry.