# Dietary Cerium (Ammonium Ceric Nitrate) Promoted the Growth, Intestinal Digestive Enzyme Activity, and Positive Modulation of Intestinal Microbiota of Largemouth Bass (Micropterus salmoides)

## TL;DR

Adding cerium to largemouth bass feed improves growth, enzyme activity, and gut bacteria balance.

## Contribution

This study identifies optimal cerium levels in fish diets to enhance growth and gut health in largemouth bass.

## Key findings

- Dietary cerium at 40 mg/kg increased weight gain and reduced feed conversion ratio in largemouth bass.
- Cerium supplementation improved intestinal protease and amylase activity and modulated gut microbiota.
- Optimal cerium inclusion levels were estimated at 57.9–60.0 mg/kg based on growth and feed efficiency.

## Abstract

Largemouth bass (Micropterus salmoides) is the most important carnivorous fish cultured in China. With the development of high-density farming, the potential risks faced are continuing to grow, and exploring green functional additives is of great significance for the healthy development of the largemouth bass farming industry. The present study investigated the impacts of supplementing cerium as the form of ammonium ceric nitrate (Ce (NH4)2(NO3)6) in feed on the growth, serum antioxidant and immune function, intestinal digestive enzyme activity, tissue morphology and microbiota of largemouth bass. The results indicated that the addition of 40 mg/kg dietary cerium significantly increased weight gain and decreased the feed conversation ratio, and the higher inclusion did not further increase the weight gain and decrease the feed conversation ratio. In summary, dietary cerium supplementation can promote the growth, intestinal digestive enzyme activity, and positive modulation of the intestinal microbial flora of juvenile largemouth bass. Based on the second-order polynomial regression analysis of WG or the FCR, the appropriate inclusion level of dietary cerium for juvenile largemouth bass was estimated to be 57.9, and 60.0 mg/kg, respectively. The findings will direct the application of rare earth additives in aquatic feeds.

This study investigated the dietary effects of cerium (ammonium ceric nitrate, Ce (NH4)2(NO3)6) on the growth, serum antioxidant, intestinal digestive enzyme activity, tissue morphology and microbiota of Micropterus salmoides. Seven diets were designed with cerium supplementation of 0 (CON), 10 (Ce10), 20 (Ce20), 40 (Ce40), 60 (Ce60), 80 (Ce80) and 120 mg/kg (Ce120), respectively. Largemouth bass juveniles (initial weight of 16.89 ± 0.04 g) were fed with the above diets for 56 days. Compared with the control group, the weight gain of the Ce40 group increased by 14.4% and the feed conversion ratio decreased by 0.13 (p < 0.05). The Ce60, Ce80 and Ce120 groups showed significantly higher superoxide dismutase activity and lower malondialdehyde concentration compared with the control group (p < 0.05). Protease activity in the Ce20 and Ce40 groups and amylase activity in the Ce40 group were markedly elevated relative to the control group (p < 0.05). The proportion of Firmicutes was increased and the proportion of Proteobacteria was decreased by the addition of 10 mg/kg and 40 mg/kg Ce (Ce10 and Ce40 groups). In summary, dietary cerium supplementation can promote the growth, intestinal digestive enzyme activity, and positive modulation of the intestinal microbial flora of juvenile Micropterus salmoides. Based on the second-order polynomial regression analysis of WG or the FCR, the appropriate inclusion level of dietary cerium for juvenile largemouth bass was estimated to be 57.9 and 60.0 mg/kg, respectively.