ENAGenomicsUniversidad Nacional del Santahttps://www.ebi.ac.uk/ena/browser/view/PRJNA1295878The feed conversion ratio of fish and insects is among the most efficient within animals, with a higher conversion of food into protein than that observed in homeotherms. This fact may play a critical role in the context of increasing demand for protein of animal origin, while simultaneously reducing the environmental impact. Arapaima gigas, one of the largest freshwater fish in the world, inhabiting the Amazon basin in South America, displays one of the most optimal feed conversion efficiencies (FCR) in fish during the initial year of the lifecycle. Consequently, we sought to ascertain whether the FCR of A. gigas could be further improved and evaluated the liver, a pivotal organ in animal nutrition. Our findings indicated that a period of fasting of one or two weeks resulted in a loss of body weight and a cessation of growth in total length. Furthermore, fasting resulted in a reduction in the size of the liver and hepatocytes. Upon refeeding, growth resumes, and by the first week of refeeding, refed fish have recovered the liver and hepatocyte size. The FCR was reduced in refed fish during the three-week phase of refeeding, and feed intake increased in the final two weeks of refeeding, with partial compensatory growth for body weight. It is noteworthy that the liver size normalized to body weight remained elevated in refed fish up to three weeks of refeeding. The total length of refed fish caught up with controls by the end of the experiment, demonstrating full compensatory growth at a rate comparable to that observed within a period of three weeks following refeeding. In conclusion, our results demonstrate that liver histology is a reliable indicator of an ongoing compensatory growth process. Furthermore, the FCR of A. gigas can be further improved and thus can be a methodology to be applied by producers in their growing aquaculture production.ENAfalsePhysiological and Transcriptomic Responses to Fasting-Refeeding in Arapaima gigas2025-07-282025-07-28PRJNA1295878