The objective of this study was to evaluate the impact of using a combination of fermented feed and commercial feed on the survival and intestinal microbiota of shrimp. In this study, a superior microbial community comprising Enterococcus faecalis, Lactobacillus plantarum, Bacillus subtilis, Saccharomyces cerevisiae, and Aspergillus niger was found based on the improvement in nutritional quality metrics (P < 0.05). Using this community, a low fish meal (LFM, 15%) shrimp fermented feed was prepared. Subsequently, a 56-day feeding trial was conducted, involving a total of approximately 100,000 individual shrimp. The shrimp were divided into 2 treatments, the control group was administered a high fish meal (30%) non-fermented diet (NFD), while the treatment group received a mixed diet (MFD) with a 2:3 fermented to non-fermented ratio. Results showed that feeding the diet MFD improved the shrimp survival (P = 0.002) but reduced yield (P = 0.032) and weight gain (P = 0.003). In the first 29 days of the feeding trial, there was no statistical difference between the groups in metrics, namely ammonia nitrogen, nitrite, pH, and total alkalinity (P > 0.05). During the last 27 days, feeding the MFD diet did not increase ammonia nitrogen or nitrite content in water (P > 0.05), and even reduced these parameters at specific sampling intervals. Similarly, water pH and total alkalinity in the MFD group showed significant elevations at particular sampling points (P < 0.05). Vibrio viridis and Vibrio flavus (common pathogenic bacteria in shrimp culture) demonstrated no population increase in water from shrimp fed the MFD diet, with significant decreases observed at specific time points compared to the NFD group (P < 0.05). Feeding the MFD modulated the features of the intestinal microbiota manifested by marked reductions in alpha-diversity indices including the observed_OTUs (P < 0.001), Chao1(P < 0.001), Shannon (P < 0.001), and Simpson (P < 0.001) indexes. Concurrently, this nutritional modulation drove a phylum-level taxonomic shift characterized by increased Proteobacteria relative abundance and decreased that of Bacteroidetes (P < 0.001). The MFD group also exhibited a notably increased ratio of Firmicutes to Bacteroidetes (P = 0.016). Additionally, the linear discriminant analysis effect size analysis revealed that Proteobacteria and Bacteroidetes served as potential biomarkers of the MFD and NFD groups at the phylum level, respectively, with Marinicellaceae and Flavobacteriaceae distinguishing them at the family level. The gut microbiota of shrimp on two feeding diets showed distinct patterns in the predicted pathways related to immune and infectious disease, with diets also affecting their phenotypic traits. Overall, combined commercial and fermented feed improved survival and modulated intestinal microbiota in L. vannamei.

The aim of this study was to evaluate the effects of wheat gluten as a substitute for fish meal (FM) and soy protein concentrate (SPC) in the low-fishmeal-based extruded diet in red spotted grouper Epinephelus akaara. Eight isonitrogenous (441–456 g kg⁻¹) and isocaloric (21.5–22.0 MJ kg⁻¹) diets were produced, including the control diet (R0), three diets with 33.3, 66.7, and 100% FM being replaced by a mixture of wheat gluten, wheat, and taurine (GWT) (RF1, RF2, RF3), three diets with 33.3, 66.7, and 100% SPC replaced by GWT (RS2, RS2, RS3) and one diet with 50% FM and 50% SPC replaced by GWT (RFS). Results showed that feed intake (FI), weight gain (WG), protein retention efficiency, and liver superoxide dismutase activity increased linearly, while feed conversion ratio (FCR) decreased linearly with the decrease of dietary FM. Additionally, FI, WG, and FCR significantly increased with decreasing dietary SPC. Overall, 100% FM or 61.2% SPC can be safely replaced by wheat gluten in the red-spotted grouper diet containing 20.0% FM and 21.4% SPC.

To address the negative effects of high-starch diets on largemouth bass (LMB), this study evaluated the feasibility of using a Gracilaria lemaneiformis-konjac glucomannan mixture (GKM, 2:1) as a substitute for strong flour (SF). Four iso-nitrogenous and iso-lipid diets were formulated: a control (15% SF; GK00) and three other diets replacing 33.3% (GK05), 66.7% (GK10), or 100% (GK15) of SF with GKM. Each diet was randomly administered to triplicate tanks of fish (10.49 ± 0.232 g) for a 10-week feeding trial. Results showed that the GKM inclusion groups significantly improved the fish survival and feed intake. Fish in GK05 and GK10 groups exhibited significantly higher final body weight, weight gain, and specific growth rate than the GK00 group, while GK15 showed no significant increase in these metrics. There was no impairment in protein, lipid, phosphorus, and energy retention efficiency in the GK05 and GK10 groups compared to those of the GK00 group. Apparent digestibility for feed dry matter, protein, lipid, phosphorus, and the 16 amino acids was not decreased in the GK05 and GK10 groups relative to the GK00 group. In addition, this study revealed reduced phosphorus waste per kilogram of weight gain in GK05 and GK10. In conclusion, these findings position GKM as a sustainable alternative to SF in feed for LMB.