The Effect of Lactococcus lactis subsp. lactis PTCC 1403 on the Growth Performance, Digestive Enzymes Activity, Antioxidative Status, Immune Response, and Disease Resistance of Rainbow Trout (Oncorhynchus mykiss).

The effect of Lactococcus lactis subsp. lactis strain PTCC 1403 as a potential probiotic was investigated on the growth, hematobiochemical, immune responses, and resistance to Yersinia ruckeri infection in rainbow trout. A total of 240 fish were distributed into 12 fiberglass tanks representing four groups (× 3 replicates). Each tank was stocked with 20 fish (average initial weight: 11.81 ± 0.32 g) and fed L. lactis subsp. lactis PTCC 1403 at 0 (control, T0), 1 × 109 (T1), 2 × 109 (T2), and 3 × 109 (T3) CFU/g feed for 8 weeks. The results showed enhanced protein efficiency ratio and reduced feed conversion ratio in the fish-fed T2 diet. Further, fish-fed T2 and T3 diets showed a significantly higher survival rate than the control (p < 0.05). Trypsin, lipase, and protease activities were increased in fish-fed L. lactis subsp. lactis PTCC 1403 compared to the control (p < 0.05). Fish fed with a T2 diet showed significantly (p < 0.05) lower glucose content than other groups. The blood lysozyme activity and IgM showed significantly (p < 0.05) higher values in fish-fed T2 and T3 diets than in other groups. The antioxidative responses were increased in fish-fed T2 and T3 diets (p < 0.05). After 7 days post-Y. ruckeri challenge, the cumulative mortality rate showed the lowest value in fish fed with T1 and T2 diets, while the highest value was recorded in the control group. In conclusion, the results revealed beneficial effects of L. lactis subsp. lactis PTCC 1403 on the feed efficiency, immune response, and resistance to Y. ruckeri infection in rainbow trout.

Design, production and purification of a novel recombinant gonadotropin-releasing hormone associated peptide as a spawning inducing agent for fish.

GnRH is a neuropeptide known to regulate reproduction in vertebrates. The purpose of this study was to design and produce recombinant gonadotropin-releasing hormone associated peptide (rGnRH/GAP) as an alternative of the previous GnRHs and native extracted hormone from tissue, to induce final maturation in fish. Decapeptide as well as GAP area sequences were compared between GnRH1, GnRH2, and mGnRH from Acipenser sp and Huso huso, respectively. Considering the conserved amino acids and the replacement of un-stable amino acids with those that were more stable against proteolytic digestion as well as had a longer half-life, the sequence was designed. The sequences of decapeptide and GAP region were synthesized and then cloned on pET28a expression vector and transformed into expression host Escherichia coli BL21(DE3). The supernatant of cultured recombinant bacteria was used for purification using TALON Metal affinity resin. The purity of the GnRH/GAP was confirmed by single 8 kDa band on SDS-PAGE and Western blot. Bioinformatics studies were performed for evaluation of homology between GnRH protein sequences and prediction of 3D protein structure using Swiss Model. The result showed that the structure prediction of the recombinant GnRH decapeptide was relatively similar to decapeptide of GnRH2 from Beluga (Huso huso). The GAP structure was similar to GAP1 of Nile tilapia (Oreochromis niloticus) and sturgeon and GnRH2 of Chinese sturgeon (Acipenser sinensis). The mass analysis showed that the sequence was exactly the same as designated sequence. Biology activity of rGnRH/GAP was tested in mature goldfish (Carassius auratus) and results showed that rGnRH/GAP had a positive effect in final maturation. Indeed 17α, 20ß-dihydroxy-4-pregnen-3-one (DHP) was increased 17 h and 24 h after injection with rGnRH/GAP and spawning stemmed from that injection. These novel findings introduce the potential of utilizing rGnRH/GAP in aquaculture.

The effect of Spirulina platensis meal on antioxidant gene expression, total antioxidant capacity, and lipid peroxidation of rainbow trout (Oncorhynchus mykiss).

The study was conducted to investigate the effect of diets containing 0, 2.5, 5, 7.5, and 10% S. platensis meal on total antioxidant capacity (TAC) and lipid peroxidation, as well as the expression of two antioxidant enzyme genes (SOD and CAT) in rainbow trout (Oncorhynchus mykiss). One hundred and eighty fish, with an average initial weight of 101 ± 8 g, were cultured for 10 weeks. At the end of experiment, lipid peroxidation significantly decreased in serum of fish fed with S. platensis and fish fed with 5, 7.5, and 10% microalgae showed a significantly lower value compared to control and 2.5%. Inclusion of 7.5 and 10% S. platensis in diet also decreased lipid peroxidation in liver. TAC significantly increased with increasing level of S. platensis. Expression level of superoxide dismutase (SOD) and catalase (CAT) genes significantly increased in the fish liver after administration of microalgae and fish fed with 10% S. platensis in diet showed the highest level compared to the other treatments. The present study reveals that inclusion of 10% S. platensis in diet can decrease oxidative stress in rainbow trout. Therefore, S. platensis can be used as potential antioxidant for fish farming.

Effect of sodium selenite on the bacteria growth, selenium accumulation, and selenium biotransformation in Pediococcus acidilactici.

In this study, the effect of low selenium concentrations on bacteria growth, selenium bioaccumulation, and selenium speciation in Pediococcus acidilactici was investigated. Six different sodium selenite (Na2SeO3) solutions with concentrations of 0, 0.5, 1, 2, 3, and 4 mg/L were added in MRS broth for 24 h. Then, the obtained bacterial pellets were weighed. The contents of total selenium and selenium species in the bacterial pellets were measured via optimized enzymatic hydrolysis and HPLC-ICP-MS. The maximum dried P. acidilactici biomass of 1.44 g/L was achieved by utilizing 1 mg/L Na2SeO3. By increasing sodium selenite concentrations, total selenium contents were significantly increased from 0.14 to 1.45 mg/g dry weight (p < 0.05). The findings indicated that selenium was favorably incorporated into the bacteria protein fraction and mainly formed selenocysteine. Therefore, selenium-enriched lactic acid bacterium P. acidilactici can deliver a less-toxic, more bioavailable selenium source for human and animal nutrition.

Effect of Potential Probiotic Lactococcus lactis Subsp. lactis on Growth Performance, Intestinal Microbiota, Digestive Enzyme Activities, and Disease Resistance of Litopenaeus vannamei.

The aims of this study were to evaluate the effects of Lactococcus lactis subsp. lactis on the growth, intestinal microbiota, digestive enzyme activity, and disease resistance of Litopenaeus vannamei. Diets containing four different concentrations of L. lactis (0 [basal diet], 106, 107, and 108 CFU g-1) were fed to white shrimps L. vannamei (average weight 5.89 ± 0.36 g) for 8 weeks. At the end of the feeding trial, shrimps were immersed in Caspian Seawater (10.8 ppt) contaminated with 106 CFU ml-1 pathogenic V. anguillarum for 2 h. Results revealed that growth rate, survival, and body protein level were increased with dietary supplementation of L. lactis. The activities of digestive enzymes (cellulose, lipase, amylase, and protease) were significantly higher in the groups fed with diets containing 107 or 108 CFU g-1 L. lactis than those in the control. The Lactobacillus and Bacillus counts were higher (P < 0.05) in the intestine of shrimps fed with L. lactis-supplemented diets. In addition, higher level of L. lactis supplementation decreased the Vibrio counts. Moreover, L. vannamei fed diet supplemented with 108 CFU g-1 of L. lactis exhibited significantly the highest hematocyte count and post-challenge survival rate (79.2 %). Collectively, these results suggest that dietary supplementation of L. lactis subsp. lactis at 108 CFU g-1 can promote growth performance, digestive enzyme activity, and disease resistance of L. vannamei.

Effects of dietary Spirulina platensis on growth performance, humoral and mucosal immune responses and disease resistance in juvenile great sturgeon (Huso huso Linnaeus, 1754).

Dietary supplementation of Spirulina platensis at different levels (0% control, 2.5%, 5% and 10%) was evaluated to find out the effects on growth performance, digestive enzyme activities, humoral and skin innate immune responses and disease resistance in the great sturgeon (Huso huso). After 8 weeks of experimental trial, growth parameters, intestinal lactic acid bacteria count, protease and lipase activities were significantly high in 10% S. platensis fed group (P < 0.05). Similarly, in this group, respiratory burst activity of leucocytes and total protein of serum were also significantly high. Furthermore, supplementation of S. platensis at 5 or 10% exhibited higher serum IgM and lysozyme activity than the other experimental groups (P < 0.05). On the contrary, serum triglycerides and number of blood lymphocytes were lower in experimental groups than that of control group. Total proteins, lysozyme, protease and esterase, as well as in vitro bactericidal activity (against Streptococcus iniae, Yersinia ruckeri, Aeromonas hydrophila and Lactococcus garviea) were significantly high in skin mucus from fish fed 5% and 10% S. platensis, while, alkaline phosphatase was significantly high in fish fed 10% S. platensis (P < 0.05). Further, fish infected with Streptococcus iniae bacteria increased mortality, but it was alleviated by a diet supplemented with S. platensis. The present results demonstrate that this dietary supplementation with S. platensis (mainly at 10% level) could be useful for maintaining the overall health status of great sturgeon.

Dietary effects of Spirulina platensis on hematological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss).

This study evaluated the effects of diets containing 0, 2.5, 5, 7.5 and 10% of Spirulina platensis on hematological and serum biochemical parameters of rainbow trout (Oncorhynchus mykiss). Fish (n=180; 101±8 g) were randomly divided into fifteen 300 L fiberglass tanks in triplicates for a period of ten weeks. The RBC, WBC, hemoglobin, total protein and albumin levels increased significantly in the groups supplemented with S. platensis. Dietary inclusion of S. platensis had no significant effects on hematocrit, cholesterol, triglyceride and lactate of the blood. HDL-cholesterol was larger in rainbow trout fed 10% S. platensis in comparison with the other diets, whereas LDL-cholesterol significantly decreased with increasing of S. platensis inclusion. Cortisol and glucose significantly decreased with increasing of S. platensis inclusion. The present results demonstrate that inclusion of 10% S. platensis can be introduced as an immunostimulant in rainbow trout diets.