Although feed cost is the greatest concern in aquaculture, the inclusion of carbohydrates in the fish diet, and their assimilation, are still not well understood in aquaculture species. We identified molecular events that occur due to the inclusion of high carbohydrate levels in the diets of genetically improved ‘Jayanti rohu’ Labeo rohita. To reveal transcriptional changes in the liver of rohu, a feeding experiment was conducted with three doses of gelatinized starch (20% (control), 40%, and 60%). Transcriptome sequencing revealed totals of 15,232 (4464 up- and 4343 down-regulated) and 15,360 (4478 up- and 4171 down-regulated) differentially expressed genes. Up-regulated transcripts associated with glucose metabolisms, such as hexokinase, PHK, glycogen synthase and PGK, were found in fish fed diets with high starch levels. Interestingly, a de novo lipogenesis mechanism was found to be enriched in the livers of treated fish due to up-regulated transcripts such as FAS, ACCα, and PPARγ. The insulin signaling pathways with enriched PPAR and mTOR were identified by Kyoto Encyclopedia of Genes and Genome (KEGG) as a result of high carbohydrates. This work revealed for the first time the atypical regulation transcripts associated with glucose metabolism and lipogenesis in the livers of Jayanti rohu due to the inclusion of high carbohydrate levels in the diet. This study also encourages the exploration of early nutritional programming for enhancing glucose efficiency in carp species, for sustainable and cost-effective aquaculture production.

Background: Feed cost mainly constitutes 40-60% of total aquaculture production expenses, due to the inclusion of expensive animal-derived ingredients to the feed industry. Studies suggested that herbivore and omnivore fish species can consume higher level of carbohydrate (150–300 g/kg starch) as compared to carnivore fish. However, lower carbohydrate utilization in fishes is less understood till date. In the present work, It was attempted to decipher the physiological changes in genetically improved rohu (Jayanti Rohu) upon inclusion of different levels of starch in the feed regime. Methods: Three isonitrogenous (24% crude protein), isolipidic (10% ether extract) experimental diets viz. TS20 (@20% starch), TS30 (@30% starch) and TS40 (@40% starch) were formulated and fed to Jayanti Rohu fingerlings (180 number with average weight of 45±3.5 g) twice daily up to satiation level for 45 days experimental period. The growth performance, nutrient utilization, histological changes and modulation of hepatic gene expressions were evaluated after completion of experiment. Result: Results indicated significantly (p less than 0.05) increased weight gain percentage, SGR and condition factor in TS30 and TS40 as compared to TS20. The histoarchitecture of hepatic cells depicted greater cell damage with increasing levels of dietary carbohydrates. The glucose membrane transporter 2 gene and carbohydrate metabolism involved genes showed a higher expression in TS40 and TS30 compared to TS20. Therefore, the present study concluded that inclusion level of 30% starch as optimal level in the diet of genetically improved Jayanti rohu.