Introduction
The onset of exogenous feeding is a critical phase in early fish larval development and is often associated with high mortality, posing challenges for aquaculture (Y��fera & Darias, 2007). In Eurasian perch (Perca fluviatilis), larvae show considerable variability in their ability to initiate foraging (Pepin et al., 2014), with some individuals feeding immediately (early eaters), others starting days later (late eaters), and some never feeding at all (non-eaters). The current study aimed at investigating the differences between eaters and non-eaters under optimal rearing conditions using a combination of zootechnical and transcriptomic approach.
Material and Methods
Six families were produced by crossing one female with one male, and larvae were reared until weaning. Starting at first feeding (5 days post-hatching, DPH), early eaters and non-eaters were manually selected and reared in separate tanks. Subsequent selections at 6 and 7 DPH enabled the identification of larvae that later initiated foraging (late eaters), thereby ensuring accurate classification of true non-eaters individuals. Total RNA was extracted from groups sampled at 6DPH, and sequenced (150 bp paired-end, 40M reads per library). Differentially expressed genes analysis was performed using DESeq2. Gene ontology enrichment (GO) was conducted with ShinyGO. Specific genes were identified for further RT-qPCR validation.
Results and Discussion
Results indicates that the failure in foraging was the primary cause of early mortality, accounting for up to 50% of larval deaths. Eaters were larger in both length and weight compared to non-eaters, indicating that body size may influence the ability to initiate foraging. RNA-seq analysis of larvae at 6 DPH identified 3,117 differentially expressed genes (DEGs; padj < 0.01, |log2FC| > 1). Principal component analysis revealed a strong separation between eaters and non-eaters along PC1, accounting for 86% of the variance. Functional annotation indicated that these DEGs are largely involved in DNA replication and cell cycle pathways. Notably, non-eaters showed down-regulation of genes associated with lipid metabolism (e.g., dhcr24, sqle, sc5d). Together, these results suggest that failure to initiate foraging is associated with growth and metabolic processes, reflecting differences in physiological condition during early larval stages. This study provides a first framework for understanding the biological basis of early foraging ability in fish larvae.
Acknowledgment
This work was funded by National Science Center of Poland (Preludium23, UMO-2024/53/N/NZ9/01570).
References
Y��fera, M., & Darias, M. J., 2007. The onset of exogenous feeding in marine fish larvae. Aquaculture, 268(1-4), 53-63.
Pepin, P., Robert, D., Bouchard, C., Dower, J.F., Falardeau, M., Fortier, L., Jenkins, G.P., Leclerc, V., Levesque, K., Llopiz, J.K. and Meekan, M.G., 2014. Once upon a larva: revisiting the relationship between feeding success and growth in fish larvae. ICES Journal of Marine Science, 72(2), pp.359-373.