# Effects of Dietary Protease Levels on Growth Performance, Feeding Regulation, Glucose and Lipid Metabolism, and Endogenous Protease Secretion in Chinese Perch (Siniperca chuatsi)

## TL;DR

Adding 1.6 g/kg protease to Chinese perch feed improves growth, digestion, and energy use by regulating genes related to appetite, glucose, and lipid metabolism.

## Contribution

Identifies optimal protease dosage (1.6 g/kg) and its molecular mechanisms in enhancing growth and feed efficiency in Chinese perch.

## Key findings

- 1.6 g/kg protease significantly improves weight gain, feed intake, and protein retention in Chinese perch.
- Protease suppresses appetite-inhibiting genes (pomc and cart) and up-regulates genes for glucose and lipid metabolism.
- Endogenous pepsinogen genes (pga1 and pgc) are maximally up-regulated with 1.6 g/kg protease, enhancing protein digestion.

## Abstract

Chinese perch (Siniperca chuatsi) aquaculture is constrained by poor artificial feed acceptance and high protein demands. While exogenous proteases enhance nutrient utilization, their optimal dosage and mechanism in this species were unknown. This study systematically investigated graded neutral protease levels (0–1.6 g/kg) over 8 weeks on growth, feed utilization, and key gene expression. Our results illustrated that 1.6 g/kg protease significantly improved weight gain, specific growth rate, feed intake, and protein retention while reducing the feed conversion ratio of Chinese perch (p < 0.05). Crucially, this dose stimulated appetite by suppressing anorexigenic genes (pomc and cart), enhanced glycolytic (gk and pk) and lipid metabolic gene (pparα) expression leading to more efficient energy utilization, and maximally up-regulated endogenous pepsinogen genes (pga1 and pgc), indicating improved protein digestion in feed. This study identifies that the addition of 1.6 g/kg protease to feed can effectively enhance the growth performance of Chinese perch by regulating the expression of appetite-regulating genes, glucose and lipid metabolism-related genes, pepsinogen genes, and deaminase genes. It provides an important theoretical basis for the development of artificial feed for Chinese perch and the improvement of aquaculture efficiency.

300 healthy Chinese perch (Siniperca chuatsi) (34.35 ± 0.47 g) were randomly divided into five groups (P1–P5) fed diets supplemented with 0, 0.2, 0.4, 0.8, and 1.6 g/kg protease for 8 weeks. Compared to P1, protease supplementation significantly up-regulated endogenous pepsinogen genes (pga1 and pgc) and down-regulated the muscle deamination gene ampd. In comparison to P1, the expression level of the hepatic gene ast increased in P2, P3, and P5, while gdh elevated in P2 and P3 (p < 0.05). Compared to P1, the expression of feeding-related gene npy decreased while pomc increased in P2; agrp increased in P3; and pomc and cart decreased in P5, resulting in significant increases in feed intake in P2, P3, and P5 (p < 0.05). Glycolytic genes (gk and pk) and lipid metabolism gene pparα were up-regulated in P2, P3 and P5, while hsl increased in P3 but decreased in P5 (p < 0.05). P5 exhibited significantly improved weight gain rate, specific growth rate, protein efficiency ratio, and protein retention rate, alongside reduced feed conversion ratio compared with P1. Therefore, dietary 1.6 g/kg protease significantly enhances growth, improves feed efficiency, stimulates pepsinogen secretion, and modulates deamination, glycolytic, and lipid metabolism genes in Siniperca chuatsi.