Effects of replacing fishmeal with cottonseed protein concentrate on growth performance, blood metabolites, and the intestinal health of juvenile rainbow trout (Oncorhynchus mykiss).

Cottonseed protein concentrate (CPC) is a potential non-food protein source for fishmeal replacement in fish feed. However, a high inclusion level of CPC in diets may have adverse effects on the metabolism and health of carnivorous fish. This study aimed to investigate CPC as a fishmeal alternative in the diet of rainbow trout Oncorhynchus mykiss based on growth performance, blood metabolites, and intestinal health. Five isonitrogenous (46% crude protein) and isolipidic (16% crude lipid) diets were formulated: a control diet (30% fishmeal) and four experimental diets with substitution of fishmeal by CPC at 25%, 50%, 75%, and 100%. A total of 600 fish (mean body weight 11.24g) were hand-fed the five formulated diets to apparent satiation for eight weeks. The results showed no adverse effects on growth performance when 75% dietary fishmeal was replaced by CPC. However, reduced growth and feed intake were observed in rainbow trout fed a fishmeal-free diet based on CPC (CPC100%). Changes in serum metabolites were also observed in CPC100% compared with the control group, including an increase in alanine aminotransferase (ALT), a decrease in alkaline phosphatase (ALP), alterations in free amino acids, and reductions in cholesterol metabolism. In addition, the CPC-based diet resulted in reduced intestinal trypsin, decreased villus height and width in the distal intestine, upregulated mRNA expression levels of inflammatory cytokines in the intestine, and impaired gut microbiota with reduced bacterial diversity and decreased abundance of Bacillaceae compared with the control group. The findings suggest that the optimum substitution rate of dietary fishmeal by CPC for rainbow trout should be less than 75%.

Effects of dietary myo-inositol on growth, antioxidative capacity, and nonspecific immunity in skin mucus of taimen Hucho taimen fry.

In this study, the effects of dietary myo-inositol on the skin mucosal immunity and growth of taimen (Hucho taimen) fry were determined. Triplicate groups of 500 fish (initial weight 5.58 ± 0.15 g) were fed different diets containing graded levels of myo-inositol (28.75, 127.83, 343.83, 565.81, and 738.15 mg kg-1) until satiation for 56 days. Thereafter, the nonspecific skin mucus immune parameters, antioxidative capacity, and growth performance were measured. The skin mucus protein and the activities of alkaline phosphatase were significantly higher than those in the control group (P < 0.05). However, there were no significant differences in lysozyme activity among the treatments (P > 0.05). The antimicrobial activity and minimum inhibitory concentration of the skin mucus were increased significantly by myo-inositol supplementation (P < 0.05). The superoxide dismutase, catalase, and glutathione peroxidase activities were significantly elevated in the treatment groups (P < 0.05), whereas the malondialdehyde contents were significantly decreased (P < 0.05). Low-level myo-inositol (28.75 mg kg-1) led to a significantly lower weight gain, feed efficiency, condition factor, and survival rate compared with the other treatments (P < 0.05). In conclusion, dietary myo-inositol deficiency (28.75 mg kg-1) adversely affects the skin mucus immune parameters, antioxidative capacity, and growth performance of Hucho taimen fry.

Effects of traditional Chinese medicines on immunity and culturable gut microflora to Oncorhynchus masou.

The present study was conducted to evaluate the effect of dietary traditional Chinese medicines on the growth, immunity, and composition of culturable gut microflora in Oncorhynchus masou. Diets were formulated to contain no medicine (control), antitoxic decoction (A), general antiphlogistic decoction (B), or Herbae Artemisiae Capillariae decoction (C). Fish were manually fed twice daily till apparent satiation for 30 days. Compared with that in the control group, supplementation with the three kinds of Chinese herbal medicine enhanced fish growth significantly (P < 0.05). The activities of liver superoxide dismutase and glutathione peroxidase in the treatment groups were significantly higher compared with those in the control group (P < 0.05). The quantity of intestinal microflora was higher in the treatment groups compared with that in the control group. Moreover, there were some effects of dietary Chinese herbal medicine on the composition of intestinal microflora. Microflora of Pseudomonas sp., Psychrobacter sp., Microbacterium sp., Macrococcus sp., Burkholderia sp., and Arthrobacter sp. were found in the treatment groups, whereas there were none in the control group. There was a significant increase in their amounts in the treatment groups (P < 0.05). The three kinds of traditional Chinese medicines can improve the growth and immunity of Oncorhynchus masou and affect the quantity and composition of intestinal microflora.

Genomic organization, expression and antimicrobial activity of a hepcidin from taimen (Hucho taimen, Pallas).

Hepcidin, an antimicrobial peptide, plays a crucial role in innate immune system of teleost fish. As a cysteine-rich peptide, hepcidin possesses a dual function including iron regulation and innate immunity. In the present study, a full-length hepcidin cDNA (HtHep) was cloned and characterized by RT-PCR and RACE techniques from taimen (Hucho taimen, Pallas), which is a type of rare, precious and cold-water fish species in China. The cDNA contains an open reading frame (ORF) of 267 bp encoding 88 amino acid (aa), with 170 bp located in the 5(') untranslated region (UTR) and 151 bp in the 3' UTR. The genomic sequences analysis showed that the HtHep gene consisted of three exons and two introns (with the length 94 and 251 bp, respectively). With a predicted molecular mass of 2881.4 Da and a theoretical pI of 8.53, the deduced amino acid encodes a signal peptide of 24 aa, prodomain of 39 aa and mature peptide of 25 aa. The signal peptidase (SA-VP) and the motif RX (K/R)R of propeptide convertase suggested the cleavage site of signal and mature peptide. Eight conserved cysteine residues were also identified and formed four disulfide bonds. Pair-wise alignments showed that HtHep clustered together with two fish species of Salmonidae family (Salmo salar and Oncorhynchus mykiss) in HAMP1 branch. Quantitative RT-PCR analysis indicated that the mRNA levels of HtHep were detected in a wide range of tissues and the highest level was detected in the liver. Its expression was also detected early during embryonic stage and could be up-regulated in the liver when challenged with pathogenic bacteria (Yersinia ruckeri). The recombinant HtHep (rHtHep) had antimicrobial activity against both gram-positive (Micrococcus lysodeikticus and Staphylococcus aureus) and gram-negative bacteria (Escherichia coli). Our results suggested that HtHep might be involved in the innate immune defense against bacterial pathogens in taimen.