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An 8-week feeding trial was conducted to evaluate the effect of replacing soybean meal (SBM) with cottonseed meal (CSM) on growth and health of grass carp. Four isonitrogenous diets containing 0, 16.64, 32.73 and 48.94% of CSM, respectively, as replacements of 0, 35, 68 and 100% of SBM were fed to fish (initial body weight 7.14 ± 0.75 g/fish) in triplicate aquaria twice daily. The results indicated that fish fed diet containing 16.64% CSM as a replacement of 35% of SBM was not affected in weight gain (WG), feed efficiency ratio (FER) and feed conversion ratio (FCR) (P > 0.05), while fish fed diets containing higher level of dietary CSM (32.73 and 48.94%) significantly decreased WG and PER and significantly increased FCR (P < 0.05). Fish fed diets containing 16.64% of CSM had significantly increased hematocrit (Ht) and hemoglobin (Hb) values compared with fish fed with other diets (P < 0.05). The activity of catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), gene expression levels of GSH-Px and CAT, and content of malondialdehyde (MDA) were significantly lower for fish fed diets containing 16.64% CSM compared with fish fed other diets (P < 0.05). These results showed 16.64% CSM could be used to replace 35% SBM in the diets of juvenile grass carp and without health impact.

The continuing emergence and development of pathogenic microorganisms that are resistant to antibiotics constitute an increasing global concern, and the effort in new antimicrobials discovery will remain relevant until a lasting solution is found. A new bacterial strain, designated JFL21, was isolated from seafood and identified as B. amyloliquefaciens. The antimicrobial substance produced by B. amyloliquefaciens JFL21 showed low toxicity to most probiotics but exhibited strong antimicrobial activities against multidrug-resistant foodborne pathogens. The partially purified antimicrobial substance, Anti-JFL21, was characterized to be a multiple lipopeptides mixture comprising the families of surfactin, fengycin, and iturin. Compared with commercially available polymyxin B and Nisin, Anti-JFL21 not only could exhibit a wider and stronger antibacterial activity toward Gram-positive pathogens but also inhibit the growth of a majority of fungal pathogens. After further separation through gel filtration chromatography (GFC), the family of surfactin, fengycin, and iturin were obtained, respectively. The results of the antimicrobial test pointed out that only fengycin family presented marked antimicrobial properties against the indicators of L. monocytogenes, A. hydrophila, and C. gloeosporioides, which demonstrated that fengycins might play a major role in the antibacterial and antifungal activity of Anti-JFL21. Additionally, the current study also showed that the fengycins produced by B. amyloliquefaciens JFL21 not only maintained stable anti-Listeria activity over a broad pH and temperature range, but also remained active after treatment with ultraviolet sterilization, chemical reagents, and proteolytic enzymes. Therefore, the results of this study suggest the new strain and its antimicrobials are potentially useful in food preservation for the biological control of the multidrug-resistant foodborne pathogens.

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