Transcriptomic Analysis Reveals Glycolysis and Gluconeogenesis Pathway Activation Underlying Growth Enhancement by Duck-Blood Protein Hydrolysate in Flowerhorn Cichlid Fish

Protein hydrolysates have potential as sustainable functional feed ingredients or additives for the aquaculture industry. This study examined the growth-promoting effects of duck-blood protein hydrolysate (DBPH, <10 kDa) on the flowerhorn cichlid (<i>Amphilophus citrinellus</i> × <i>Cichlasoma trimaculatum</i>). Fish with an average weight of 3.24 ± 0.22 g were randomly assigned to four dietary treatments: a negative control (basal diet) and basal diets supplemented with 0.5%, 1%, and 2% DBPH. After 90 days of the feeding trial, growth parameters indicated that supplementation with 1% and 2% DBPH enhanced growth. However, the muscle composition and skin coloration did not differ significantly. Transcriptome sequencing of the liver tissue yielded 39.83 GB of high-quality clean data. De novo transcriptome assembly identified 32,824 unigenes, of which 21,385 were successfully annotated based on public databases. Differential expression analysis identified 269 upregulated and 232 downregulated genes. To clarify the growth-promoting effects of DBPH, five glycolysis/gluconeogenesis-related genes (<i>tpi</i>, <i>gapdh</i>, <i>pck1</i>, <i>ldh</i>, and <i>adh</i>) were validated by liver qRT-PCR, and the results were consistent with those of the transcriptomic analysis. These findings provide new insights into the mechanisms by which DBPH supplementation could enhance growth, as evidenced by alterations in glycolysis and gluconeogenesis pathways, indicating potential as a novel feed additive in aquaculture.