The dietary effects of replacing fish meal with enzymatic cottonseed protein (ECP) on the growth performance, immunity, antioxidant, and intestinal health of Chinese soft-shelled turtles have not been explored. An eight-week feeding trial was conducted with a quadruplicated group of turtles ( 3.44 ± 0.01   g ) that were randomly assigned to 16 cages ( 0.6   m × 0.6   m × 0.6   m ) with 30 turtles that were stocked in each cage. Four dietary groups were fed with diets supplemented with 0, 2%, 4%, and 6% (ECP0 group (control group), ECP2 group, ECP4 group, ECP6 group) of enzymatic cottonseed protein replacing fishmeal. The present study illustrated that the final weight and WG in the ECP2 and ECP4 groups were significantly increased ( P < 0.05 ) compared with the control group. The ECP2, ECP4, and ECP6 groups significantly reduced the feed coefficient ( P < 0.05 ) and significantly increased the SGR ( P < 0.05 ). The serum TP and ALB of the ECP4 group were significantly increased ( P < 0.05 ). The ECP2, ECP4, and ECP6 groups significantly increased the activity of intestinal pepsin ( P < 0.05 ), and the activity of intestinal lipase of the EPC4 group was significantly increased ( P < 0.05 ). The intestinal villus height of the EPC4 group and EPC6 group, the villus width of the EPC2 group and EPC4 group, and the intestinal muscle thickness of the EPC4 group were significantly increased ( P < 0.05 ). At the same time, replacing fishmeal with enzymatic cottonseed protein also affected the intestinal inflammation-related genes compared with the control group. Besides that, the expression of the IL-10 gene in the experimental group was significantly upregulated ( P < 0.05 ). Nevertheless, the expression of TNF-α and IL-8 genes in the ECP2 group and TNF-α and IL-1β genes in the ECP4 group was significantly downregulated ( P < 0.05 ). In summary, replacing fish meal with enzymatic cottonseed protein positively affects the growth, immunity, and intestinal health of Chinese soft-shelled turtles. The appropriate proportion of enzymatic cottonseed protein to replace fish meal in turtle feed is 4%.

In order to explore the effects of probiotics on the water quality, growth performance, nonspecific immunity, digestion, and intestinal flora of Macrobrachium rosenbergii in the biofloc culture system, three groups (six replicates in each group) were set up and divided into no bacteria (control group, Con), Bacillus subtilis (BS), and effective microorganisms (EM) in the current experiment. After dissolution of the water, the carbon source (glucose) was evenly sprayed in the aquaculture tank to construct a biofloc with a C/N of 15. A total of 1260 giant freshwater prawn (Macrobrachium rosenbergii) with an initial body weight of (2.09 ± 0.03) g were randomly assigned to 18 tanks (70 per tank). BS group and EM group significantly reduced total nitrogen concentration. Both BS and EM groups significantly increased final mean body weight, weight gain, and specific growth rate, but significantly decreased feed conversion rate of Macrobrachium rosenbergii. BS group significantly increased plasma superoxide dismutase, lysozyme, and acid phosphatase contents, but significantly decreased plasma malonaldehyde content. EM group significantly increased serum acid phosphatase content and intestinal trypsin activity but significantly decreased the Chao and ACE index of species richness. BS group and EM group significantly decreased the abundance of Chloroflexi and Verrucomicrobiota. BS group significantly increased the abundance of Bacillus. Overall, adding probiotics affected water quality, Macrobrachium rosenbergii performance, and microbial community. The results showed that Bacillus subtilis is a good biofloc probiotic additive.

Microalgae play an important role in the formation of biofloc. To demonstrate the feasibility of Chlorella pyrenoidosa in biofloc formation, an experiment was performed with a simple random design consisting of five inoculation levels (in triplicate) of C. pyrenoidosa (0, 1 × 108, 1 × 109, 5 × 109, and 1 × 1010 cells·L−1) in the biofloc system. All treatments kept a C:N ratio of approximately 15:1. This study observed the effects of different initial concentrations of C. pyrenoidosa on biofloc formation, water quality and bacterial community in biofloc systems. The results indicated that C. pyrenoidosa had the ability to enhance biofloc development, especially when the C. pyrenoidosa initial concentration reached 5~10 × 109 cells·L−1. Too high or too low a concentration of C. pyrenoidosa will adversely affect the formation of biofloc. The effect of C. pyrenoidosa addition on water quality (TAN, NO2−-N, and NO3−-N) was not significant in the final stage. The inoculation of C. pyrenoidosa decreased the species richness and diversity of the bacterial community but increased the domination of Proteobacteria and Bacteroidota in the biofloc system, especially the order of Rhizobiales. The addition of C. pyrenoidosa could maintain water quality by increasing the proportion of several denitrifying bacteria, including Flavobacterium, Chryseobacterium, Pseudomonas, Brevundimonas, Xanthobacter, etc. These above dominant denitrifying bacteria in the biofloc system could play a major role in reducing the concentration of NO2−-N and NO3−-N. So, we recommended the reasonable concentration is 5~10 × 109 cells·L−1 if C. pyrenoidosa is used to rapidly produce biofloc.

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