# Ontogenetic Changes in the Digestive Capacities of the Naozhou Stock of Large Yellow Croaker (Larimichthys crocea)

## TL;DR

This study tracks how young large yellow croaker develop their digestive systems as they transition from relying on yolk to eating live prey and then artificial diets.

## Contribution

The study provides new insights into the ontogenetic changes in digestive and metabolic capacities during early development of large yellow croaker.

## Key findings

- Protease activity increases sharply with the introduction of live prey, while amylase and lipase activities rise during transition to formulated feeds.
- Transcriptomic and metabolomic analyses reveal coordinated changes in digestion, metabolism, and energy use across developmental stages.
- Digestive enzyme activities, gene expression, and metabolite profiles enable a smooth transition from yolk dependency to artificial diets.

## Abstract

Young fish are fragile in their early days, and many do not survive because their bodies are still figuring out how to handle different kinds of food. In this study, the young large yellow croaker grows from the stage where they rely on their yolk for nourishment to the point where they can eat tiny live animals and eventually a prepared diet. The study tracked how their digestive system developed and how they used nutrients at each step. The study found out that they start by depending on simple internal food reserves, then quickly strengthen their ability to break down proteins and fats once they begin eating live prey, and finally, they learn to handle more complex diets as their organs mature. The study also finds that changes in digestion were closely tied to shifts in growth, energy use, and organ development. These findings provide new insights into the early nutritional development of NZ large yellow croaker and provide a scientific basis for the improvement of artificial aquaculture seed production.

This study examined the digestive and metabolic responses of Naozhou (NZ) stock large yellow croaker (Larimichthys crocea) larvae and juveniles under five developmental feeding stages (DAH3, DAH7, DAH12, DAH19, DAH49) to clarify mechanisms of early nutritional adaptation. Digestive enzyme assays, transcriptome sequencing, and metabolomics were integrated to compare physiological changes across diets. Protease activity increased sharply from DAH7–19 with the introduction of rotifers, Artemia, and copepods, while amylase and lipase activities rose at DAH19–49, reflecting enhanced carbohydrate and lipid utilization during transition to formulated feeds. Transcriptomic analysis showed that differentially expressed genes were enriched in pathways involving protein digestion, lipid and energy metabolism, and cell cycle regulation. The metabolomic analysis further highlighted dynamic changes in amino acid, lipid, carbohydrate, and vitamin metabolism, consistent with transcriptomic findings. The integrated analysis suggests that the coordinated modulation of digestive enzyme activities, gene expression, and metabolite profiles enabled a smooth transition from yolk dependency to live prey feeding and a subsequent use of artificial diets. These findings provide new insights into the early nutritional development of NZ large yellow croaker and provide a scientific basis for the improvement of artificial aquaculture seed production.