A comparative feeding study on two emerging marine aquaculture species in Latin America, the common snook (Centropomus undecimalis) and the yellowtail snapper (Ocyurus chrysurus), found a striking species contrast in carbohydrate handling: at high dietary starch inclusion (~20%), common snook showed induced digestive amylase, elevated hepatic glucokinase activity and mRNA, increased hepatic glycogen and whole-body lipid, and improved feed efficiency, whereas yellowtail snapper showed prolonged and higher postprandial hyperglycemia (glycemic peak ~14.1 mmol L⁻¹ at ~9 h versus ~7.8 mmol L⁻¹ at ~6 h in snook) with poor tissue carbohydrate storage. The study leaves three linked questions open: whether the hyperglycemia of O. chrysurus reflects insulin secretion dynamics or peripheral insulin sensitivity (glucose uptake) and what explains the species difference in glucokinase transcriptional induction and glucose clearance; what carbohydrate inclusion levels and sources are optimal for each species; and what the longer-term consequences of carbohydrate-induced lipid and glycogen deposition are for fish health, flesh quality, and nitrogenous waste under commercial regimens.

Background

Both species are high-value tropical marine carnivores of the western Atlantic and Gulf of Mexico considered candidates for aquaculture diversification in Latin America: the common snook (Centropomus undecimalis, family Centropomidae) and the yellowtail snapper (Ocyurus chrysurus, family Lutjanidae). Like other strict carnivores, their feeds depend heavily on expensive protein sources such as fish meal, so replacing part of the dietary protein with cheaper digestible carbohydrate is economically attractive whenever it is physiologically tolerated. In aquaculture nutrition this is called protein sparing: dietary carbohydrate or lipid supplies energy so that dietary protein is shifted from fuel use toward tissue growth. It is conventionally quantified by feed efficiency (FE, weight gain divided by dry feed intake) and protein efficiency ratio (PER, weight gain divided by crude protein intake). A well-documented obstacle across carnivorous fishes is glucose intolerance: after a carbohydrate-rich meal, blood glucose rises high and returns to baseline only slowly (prolonged postprandial hyperglycemia), and the physiological causes — weak insulin action, limited glucose uptake by peripheral tissues, or constrained hepatic processing — remain debated across species. Key hepatic control points include glucokinase (GK), the enzyme that phosphorylates absorbed glucose inside liver cells and thereby commits it to storage or further metabolism (its abundance at both enzyme-activity and gene-expression levels, the latter typically measured by quantitative PCR, qPCR, indicates transcriptional induction), and the pentose phosphate pathway enzymes glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), which generate the reducing power used for converting carbohydrate into lipid. Dietary carbohydrate that is processed but not oxidized accumulates as hepatic glycogen (the liver's glucose polymer store) or as whole-body lipid, with potential consequences for fish health, carcass or flesh quality, and, when carbohydrate successfully spares protein, for reduced nitrogenous waste excretion into the environment. Digestibility on the gut side depends on amylase, the starch-hydrolyzing digestive enzyme, whose induction by dietary starch varies among carnivores. Arenas and colleagues (Aquaculture 543:736958, 2021) fed juveniles of both species, in a replicated 75-day trial at ~28 °C, diets with low versus high digestible starch content (~20% in the high-carbohydrate diet) and measured growth, FE and PER, intestinal amylase, a panel of hepatic carbohydrate-metabolism enzymes (GK, hexokinase, pyruvate kinase, fructose-1,6-bisphosphatase, G6PDH, 6PGDH), GK mRNA by qPCR, hepatic glycogen, whole-body proximate composition, and serial postprandial blood glucose over 24 h. In C. undecimalis the high-carbohydrate diet produced a coherent, mechanistically linked response — higher amylase, higher GK activity and GK mRNA, induced pentose phosphate pathway enzymes, more hepatic glycogen and whole-body lipid, and improved FE and PER. In O. chrysurus the same diet produced poor glycemic control: the glucose curve peaked later and nearly twice as high (~14.1 mmol L⁻¹ at ~9 h versus ~7.8 mmol L⁻¹ at ~6 h in snook) and cleared slowly, without comparable tissue carbohydrate storage; hepatic GK enzyme activity increased with the high-carbohydrate diet in both species, but GK mRNA induction occurred only in C. undecimalis. The study therefore established a sharp, unexplained species contrast in glucose tolerance between two fishes of similar thermal physiology and feeding habits, leaving the mechanistic and applied questions that define this problem unresolved. Related recent work in other carnivorous species (e.g., coho salmon fry, mandarin fish under saline-alkali stress) continues to document diet-level carbohydrate effects on glycometabolism.

Problem Statement

The problem, left unresolved by the source study, is to establish whether and how digestible carbohydrate can be used as a non-protein energy source in practical feeds for juvenile common snook (Centropomus undecimalis) and yellowtail snapper (Ocyurus chrysurus), resolving three linked open questions that bear on evidence-based, species-specific carbohydrate feeding recommendations for these two emerging aquaculture species: (1) the mechanistic core: determine whether the prolonged and higher postprandial hyperglycemia and slow glucose clearance of O. chrysurus after a starch-rich meal arise from insulin secretion dynamics, from peripheral insulin sensitivity (insulin resistance) and glucose-uptake pathways, or from a combination, and explain the species difference from C. undecimalis in hepatic glucokinase transcriptional induction and overall glucose clearance; (2) determine, for each species, the dietary carbohydrate inclusion level that maximizes growth and feed utilization (protein sparing) while keeping postprandial glycemia within the range observed in C. undecimalis, and the effects of different carbohydrate sources on growth, feed utilization, and glucose metabolism, with particular emphasis on O. chrysurus, where poor glycemic control and lack of tissue carbohydrate storage were observed; and (3) evaluate the longer-term consequences of the carbohydrate-induced increases in whole-body lipid and hepatic glycogen observed in C. undecimalis for fish health, flesh quality, and nitrogenous waste production under commercial feeding regimens. The three sub-questions are jointly posed as parts of a single task. For (2), the target is a bounded inclusion range and a source recommendation judged against the stated glycemia criterion rather than a data-derived exact optimum.

References

  1. Martín Arenas, Alfonso Álvarez-González, Alvaro Barreto, Adolfo Sánchez, Jaime Suárez-Bautista, Karla Escalante, Gabriela Gaxiola (2021). Effect of dietary carbohydrates on growth performance, feed efficiency and glucose metabolism in common snook (Centropomus undecimalis) and yellowtail snapper (Ocyurus chrysurus) juveniles. Aquaculture 543:736958. DOI: 10.1016/j.aquaculture.2021.736958. https://doi.org/10.1016/j.aquaculture.2021.736958
  2. Angel Rojo-Cebreros, Leonardo Ibarra-Castro, Carlos Rosas, Ángel Escamilla, Honorio Cruz, Cristina Pascual, Alexis Trotter (2026). Aquaculture and conservation of the common snook Centropomus undecimalis in southeastern Mexico: a review of research at UMDI Sisal. Latin American Journal of Aquatic Research 54(1):1–14. DOI: 10.3856/vol54-issue1-fulltext-3454. https://doi.org/10.3856/vol54-issue1-fulltext-3454
  3. Stephanie F. Velasquez, Leonardo Ibarra-Castro, Alexis Weldon, Donald Allen Davis (2024). Effects of Different Protein and Lipid Levels in Practical Diets for Yellowtail Snapper, Ocyurus chrysurus (Bloch, 1971). Journal of Marine Science and Engineering 12(11):2009. DOI: 10.3390/jmse12112009. https://doi.org/10.3390/jmse12112009
  4. Alvaro Barreto, Martín Arenas, Alfonso Álvarez-González, Jaime Suárez-Bautista, Adolfo Sánchez, Carlos Maldonado, Gerard Cuzon, Gabriela Gaxiola (2024). Evaluation of in vitro and in vivo digestibility of potential feed ingredients for juvenile Yellowtail Snapper. North American Journal of Aquaculture 86(2):179–192. DOI: 10.1002/naaq.10316. https://doi.org/10.1002/naaq.10316
  5. Martín Arenas, Carlos Alfonso Álvarez-González, Alvaro Barreto, Adolfo Sánchez-Zamora, Jaime Suárez-Bautista, Gerard Cuzon, Gabriela Gaxiola (2021). Physiological and metabolic protein-sparing effects of dietary lipids on common snook Centropomus undecimalis (Bloch, 1792) juveniles. Aquaculture Nutrition 27(4):1089–1102. DOI: 10.1111/anu.13250. https://doi.org/10.1111/anu.13250
  6. Hairui Yu, Lingyao Li, Leyong Yu, Abdur Rahman, Govindharajan Sattanathan (2025). Effects of dietary carbohydrate level on growth performance, glucose metabolism, antioxidant capacity, immune response, and digestive function in coho salmon Oncorhynchus kisutch (Walbaum, 1792) fry. Aquaculture Reports 43:102917. DOI: 10.1016/j.aqrep.2025.102917. https://doi.org/10.1016/j.aqrep.2025.102917
  7. Yufu Kong, Jinquan Fan, Yan Li, Erchao Li, Liqiao Chen, Xiaodan Wang (2026). Effects of Different Carbohydrate Level Diets on Growth Performance and Glycometabolism in Mandarin Fish (Siniperca chuatsi) Under Saline-Alkali Stresses. Aquaculture Nutrition 2026:3315751. DOI: 10.1155/anu/3315751. https://doi.org/10.1155/anu/3315751
  8. Martín Arenas, Alvaro Barreto, María Gabriela Gaxiola-Cortés (2022). Habilidad de tres especies de peces tropicales de hábitos carnívoros para utilizar carbohidratos: Robalo blanco (Centropomus undecimalis), Mero rojo (Epinephelus morio) y Pargo canané (Ocyurus chrysurus). Investigación e Innovación en Nutrición Acuícola, Vol. 1 Núm. 1 (2022), pp. 263–277. Universidad Autónoma de Nuevo León. https://nutricionacuicola.uanl.mx/index.php/acu/article/view/371