Abstract:
Production of European eel offspring has become a reality, but liquid diets during larval
culture hold new challenges. This study focused on increasing food amounts without compromising
well-being or healthy larvae-bacteria interactions. First-feeding larvae were fed two food amounts
(Low = 0.5 mL food/L water vs. High = 1.5 mL food/L water) until 30 days post-hatch (dph). Results
indicated that ~75% of larvae ingested the diet in both treatments, but upregulation of a stress/repairrelated
gene (hsp90) on 25 and 30 dph indicated nutritional inadequacy. Larvae fed a High amount
of food were 3.68% bigger, while larvae in the Low-food group showed 45.2% lower gut fullness
and upregulated expression of the gene encoding the “hunger hormone” ghrelin (ghrl), indicating
signs of starvation. The High-food group larvae exhibited a healthier bacteriome with a higher
abundance of potentially beneficial orders (Lactobacillales and Bacillales), whereas the Low-food
group showed more potentially harmful orders (Vibrionales, Rhodobacterales, and Alteromonadales).
While survival was initially lower in the High-food group, both treatments had comparable survival
by the end of the experiment. In conclusion, feeding European eel larvae with High food amounts
seemed beneficial, supported by increased gut fullness, reduced ghrl expression (no starvation),
enhanced growth, and the presence of a healthier bacteriome.
