Mehdi Soltani

Present study aimed to investigate the efficacy of dietary supplementation with caffeic acid and Bacillus coagulans on growth performance, digestive enzymes, and immunity of common carp (Cyprinus carpio), and also fish resistance against Aeromonas hydrophila. Fish (21.0 ± 0.5 g) divided into four groups: control group (CD, commercial basal diet), caffeic acid (CA, 5 g/kg feed), B. coagulans (BC, 2×107 CFU/g feed), and CA+BC (5 g/kg + 2×107 CFU/g feed) for 8 weeks, followed by a 14-day challenge with A. hydrophila. A significant enhancement was obtained in growth performance of all treated groups compared to CD (P < 0.05). Also, feed conversion ratio was significantly reduced in treated fish compared to CD group (P < 0.05). Fish of BC and CA+BC groups revealed an increase in activity of amylase, lipase, protease, trypsin, and chymotrypsin in the intestinal tissue. In addition, amylase, lipase, protease, and trypsin in CA group exhibited a higher activity than CD (P < 0.05). A lower decrease in aspartate aminotransferase and a higher increase in alkaline phosphatas were observed in BC and CA+BC groups than CD group (P < 0.05). Values of total protein, total immunoglobulin, lysozyme activity, and alternative complement pathway (ACH50) were higher in sera of BC and CA+BC groups than CD (P < 0.05). Additionally, expression of genes related to lysozyme, IL-1β, IL-8, TNF-α, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in liver tissues of treatment groups were upregulated better than CD (P < 0.05). Furthermore, a significant reduction in mortality was observed in treatment groups compared to CD under the A. hydrophila challenge. These results exhibited that including a combination of caffeic acid and B. coagulans as functional dietary supplements in diet favors common carp health status and growth and, thus, can be recommended in the fish diet.

Background
Astaxanthin is the most prevalent carotenoid in the marine environment and is widely used as an additive in formulated aquafeeds.

Objectives
A 60-day feeding trial was conducted to consider the effect of dietary nanoliposome-coated astaxanthin (NA) on haematological parameters, serum antioxidant activities and immune responses of rainbow trout, Oncorhynchus mykiss.

Methods
A total of 450 healthy fish weighing 31.00 ± 2.09 g were randomly assigned in triplicate (30 fish per replicate) to 5 dietary treatments: 0 (control), 25.00, 50.00, 75.00, and 100.00 mg kg−1 NA.

Results
Fish fed the diet supplemented with 50.00 mg kg−1 NA exhibited the highest values of red blood cells, white blood cells, haemoglobin and haematocrit of 1.64 ± 0.01 × 106 mm−3, 5.54 ± 0.21 × 103 mm−3, 8.73 ± 0.24 g dL−1 and 46.67% ± 0.88%, respectively, which were significantly higher than those fed the basal diet (p < 0.05). The lowest and highest percentages of lymphocytes (67.67% ± 0.33%) and neutrophils (27.33% ± 1.20%) were also obtained in fish fed 50.00 mg kg−1 NA compared to those fed the basal diet (p < 0.05). Fish receiving diet supplemented with 50.00 mg kg−1 NA revealed the highest serum activity in superoxide dismutase, catalase, glutathione peroxidase, lysozyme and alternative complement and the lowest level of total cholesterol, cortisol, aspartate aminotransferase and alanine aminotransferase than fish receiving the basal diet (p < 0.05). Serum immunoglobulin (Ig) and ACH50 contents significantly increased with increasing dietary NA supplementation to the highest values of 43.17 ± 1.46 and 293.33 ± 2.03 U mL−1, respectively, in fish fed diet supplemented with 50 mg kg−1 NA (p < 0.05).

Conclusions
Supplementation of NA in rainbow trout diet at 50 mg kg−1 exhibited a positive effect on haematological parameters, antioxidant capacity and immune responses. Administration of such dosage can enhance rainbow trout immune responses against unfavourable or stressful conditions, for example disease outbreaks, hypoxic condition, thermal stress and sudden osmotic fluctuations, which usually happen in an intensive culture system.

An increase in the consumption of food fish, combined with a decrease in the harvest of fish, is driving the aquaculture industry at a fast pace. In parallel with the growth in the aquaculture sector and resulting stresses, the prevalence of diseases in farmed fish can increase. Although effective administration and prophylaxis are the main factors safeguarding fish species against diseases, recent approaches to mitigate the response caused by typical stressors include the uses of dietary additives. Microalgae are one of the main sources of nutrients, namely protein, lipids, vitamins, minerals, and pigments in aquatic animal diets. Numerous studies have proved the beneficial effects of microalgae on fish growth performance, feed utilization, disease resistance, and immunological and antioxidant activities. On the other hand, the administration of different microalgae to fish feed can enhance the fillet quality from several aspects, leading to an overall improvement in fillet shelf-life. This review focuses on the evidence supporting the beneficial effects of various microalgae on biochemical and organoleptic aspects as well as the proximate composition of carcasses in fish species.

The current research aimed to shed light on the efficacy of Escherichia coli strain Nissle 1917 (EcN) on goldfish (……) growth, gut immunity, morphology, bacterial nutritional enzyme activity and resistance to Aeromonas hydrophila infection. Fish fed with EcN at 106, 107 and 108 CFU/g feed for 80 days showed an enhancement in growth better than control fish. The gut innate immunity in terms of lysozyme activity, immunoglobulin and total protein levels was increased in the treatment fish with the best result being observed in fish fed EcN at 108 CFU/ g. In addition, an increase was noted in the upregulation of immune-relevant genes, namely lysozyme, interleukin-1β, inducible nitric oxide synthase and tumor necrosis factor α of fish intestine. A marked surge in the number of proteolytic and heterotrophic bacteria was noted in the gut of fish nourished with the probiotic. Histological studies exhibited an improvement in the intestinal absorption surface area, intraepithelial lymphocyte count and goblet cell density. Significantly higher survival rate was obtained in fish fed EcN at 108 CFU/g compared with the fish fed with the basal diet. These data exhibited the beneficial effect of EcN on goldfish growth, digestive enzymes, intestine heterotrophic bacteria and resistance against Aeromonas hydrophila challenge. This study confirmed the favorable outcomes resulting from the administration of EcN at108 CFU/g.The current research aimed to shed light on the efficacy of Escherichia coli strain Nissle 1917 (EcN) on goldfish (……) growth, gut immunity, morphology, bacterial nutritional enzyme activity and resistance to Aeromonas hydrophila infection. Fish fed with EcN at 106, 107 and 108 CFU/g feed for 80 days showed an enhancement in growth better than control fish. The gut innate immunity in terms of lysozyme activity, immunoglobulin and total protein levels was increased in the treatment fish with the best result being observed in fish fed EcN at 108 CFU/ g. In addition, an increase was noted in the upregulation of immune-relevant genes, namely lysozyme, interleukin-1β, inducible nitric oxide synthase and tumor necrosis factor α of fish intestine. A marked surge in the number of proteolytic and heterotrophic bacteria was noted in the gut of fish nourished with the probiotic. Histological studies exhibited an improvement in the intestinal absorption surface area, intraepithelial lymphocyte count and goblet cell density. Significantly higher survival rate was obtained in fish fed EcN at 108 CFU/g compared with the fish fed with the basal diet. These data exhibited the beneficial effect of EcN on goldfish growth, digestive enzymes, intestine heterotrophic bacteria and resistance against Aeromonas hydrophila challenge. This study confirmed the favorable outcomes resulting from the administration of EcN at108 CFU/g.

Microbiological properties, proximate composition, total volatile base nitrogen (TVB-N), pH, fatty acid (FA) composition, peroxide value (PV), free fatty acids (FFA), histamine and water holding capacity (WHC) in fresh and frozen-stored (3, 6, and 12 months at -18 ???C) fillets of rainbow trout (Oncorhynchus mykiss) (170.46 ?? 1.16 g) fed diets containing 50 mg vitamin E (control) alone or with 200 mg vitamin E (VE), 500 mg probiotic (PR), 50 mg astaxanthin (AS) and 500 mg rosemary extract (RE) kg- 1 for 4 months were assessed. Decreasing trends in fillet WHC (specially in control and AS groups) were observed in the 12-month storage. Although a low increase in fillet bacterial population occurred during the storage time in all groups, lower bacterial counts were observed in PR group. Fillet histamine, TVN and pH levels were in the accepted ranges in all treatments during the storage. Also, FFA level and proximate composition of fillets didn???t show any significant change during the storage time. The PR diet controlled microbiological activity and variations of pH and PV of fillet samples better than the other experimental diets. It also prepared an appropriate FA composition and retained the desired amounts of both n-3 and n-6 polyunsaturated fatty acids (PUFAs) in fish fillets until the end of storage period, while no significant differences were seen in values of TVN, pH, FFA and histamine among the treatments. However, AS and RE diets tended to be less functional maintaining the fillet quality during the storage time than the other experimental diets. According to the results, a diet containing 500 mg bacilli probiotic with 50 mg vitamin E kg- 1 could be highly efficient in maintaining a good quality of trout fillet stored at - 18???C for 12 months.

Studies describing antagonistic activity and disease resistance efficacy of potential probiotics towards lactococcosis caused by Lactococcus garvieae, Lactococcus lactis, Lactococcus piscium, and Lactococcus raffinolactis are limited. Most studies have focused on lactic acid bacteria (LAB), and less attention has been paid to Bacillus probiotics or other gram-positive or gram-negative members. Lactobacillus, Lactococcus, Leuconostoc, and Enterococcus are the most common genera of LAB tested towards L. garvieae either in in vitro or in vivo assays, and the obtained results are promising. Although strains of Flavobacterium, Pseudomonas, Aeromonas, and Vibrio genera have shown antibacterial activity against L. garvieae, further work is required to confirm such inhibition activity, particularly by disease resistance bioassays. recently, gram-positive or gram-negative bacteria strains have demonstrated antimicrobial inhibition towards L. garvieae in postbiotics, but details of their mode of action warranted further studies. This review addresses the probiotic therapy for lactococcosis in aquaculture and discusses the present gaps.

BACKGROUND: Infectious diseases and microbial antibiotic resistance are the major problems of fish farming industry annually causing remarkable losses. Apart from the economic losses caused by these infections, some of these agents are zoonotic and may be transmitted to humans. OBJECTIVES: This study was aimed to identify the common causative agents of infections in rainbow trout farms and to determine their antibiotic resistance toward some common antibiotics. METHODS: Sampling was performed during a nine-month period between March and December 2021 by visiting and inspecting rainbow trout farms and the affected fish with disease symptoms were obtained from the farmed fish in Mazandaran, Lorestan, Chaharmahal and Bakhtiari and Zanjan provinces. Bacterial culture was undertaken from anterior kidney or spleen organs and the isolated bacterial strains were identified by phenotyping, biochemical and molecular assays. Antibiotic resistance pattern was evaluated by disk diffusion method (DDM) and minimum inhibition concentration against erythromycin, oxytetracycline, florfenicol, enrofloxacin and nitrofurantoin. RESULTS: Seventy-four bacterial isolates of Gram-positive cocci or Gram-negative coccobacilli were isolated. In phenotyping, biochemical and molecular (PCR) assays Lactococcus garvieae (12 isolates, 16.2 %), Aeromonas hydrophila (9 isolates, 12.2 %), Streptococcus iniae (17 isolates, 23 %), Streptococcus agalactiae (20 isolates, 27 %), and Yersinia ruckeri (16 isolates, 21.7 %) were identified. The majority of these isolates were obtained from the fish farms in Mazandaran province. Erythromycin and oxytetracycline with 87.8 % resistance were antibiotics with the highest resistance, while enrofloxacin with 24.3 % resistance revealed the lowest level of resistance. Antibiotic resistance rates for florfenicol and nitrofurantoin were also 43.2 % and 44.4 %, respectively. The highest antibiotic resistance was detected in the bacterial isolates of Lactococcus garvieae, Aeromonas hydrophila, Streptococcus iniae, Streptococcus agalactiae and Yersinia ruckeri, respectively. CONCLUSIONS: This study shows that the spread of streptococcosis, lactococcosis, yersiniasis and Aeromonas septicemia and their frequent treatments has led to an increase in antibiotic resistance, especially against commonly used drugs such as erythromycin and oxytetracycline.

Background

The beneficial effects of Bacillus subtilis on growth, immune response, and disease resistance against various diseases in different fish species have been proved. However, there are no data concerning this probiotic effect on skin mucosal immunity in fish infected with Ichthyophthirius multifiliis (Ich). Ich has a high mortality rate in both edible and ornamental fish and consequently is concerned with heavy economic losses.

Objectives

Thus, we assessed the efficacy of live and heat-killed B. subtilis on skin immunity and histopathology in goldfish (Carassius auratus) infected with Ich.

Methods

Goldfish (144 fish, 2.38 g average weight) were stocked in nine glass tanks each in three replicates. Fish were fed 109 CFU g−1 live or heat-killed B. subtilis for 80 days.

Results

Probiotic administration in both viable and non-viable forms could enhance the growth performance in goldfish. Probiotic therapy also reduced the density of the parasite and histopathological level on skin and gill tissues of the treated fish. Real-time polymerase chain reaction analysis showed a higher expression of lysozyme and tumour necrosis factor-α in the treated groups compared to the control group.

Conclusions

These data demonstrated the beneficial effect of B. subtilis as probiotic and paraprobiotic on growth performance and disease resistance to Ich infestation in goldfish.

Aeromonas hydrophila is a bacterium associated with many diseases and disorders such as fin rot, skin ulcers and lethal hemorrhagic septicemia in fish. It bears several virulence factors including type III secretion system (T3SS), aerolysin, cytolytic enterotoxin and enzymes (e.g., hemolysins, lipase) that seem to play an important role in its pathogenesis. Detection of virulence markers by polymerase chain reaction (PCR) is a key procedure in defining the pathogenic ability of pathogenic bacteria and preparing a vaccine for its treatment. In this sense, this study was aimed to determine the frequency of virulence genes in isolates obtained from infected cultured carps in Khuzestan province. Out of 200 moribund carps with septicemic symptoms, 125 isolates were belonged to the motile aeromonads and 59 isolates were identified as A. hydrophila by biochemical methods. Finally, using PCR analysis, 31 isolates were identified as A. hydrophila. Five virulence genes were detected in these isolates including hemolysin, aerolysin, cytolytic enterotoxin and T3SS (aopB and ascV) by specific primers. Results showed that 23 (74.19%), 18 (58.06%), 16 (51.61%), 13 (41.63%) and 10 (32.25%) isolates possessed cytolytic enterotoxin, hemolysin, aerolysin, and T3SS genes, respectively. The results of the present study showed that among 31 isolates, only five isolates had all of dominant virulence genes. Thirteen other isolates had genotypes including hlyA+, aerA+, and act+. The remaining isolates had at least one virulence gene. This study showed that determination of the virulence genes by PCR can be a reliable method to identify a potential pathogenic Aeromonad strain.

Efficacy of orally used of red yeast (Phaffia rhodozyma) (1.6 mg astaxanthin/g product) at 15.5 g (P1), 37.3 g (P2) and 47 (P3) g per kg diet were studied on performance, carcass composition, antioxidant activity and fillet pigmentation in rainbow trout (Oncorhynchus mykiss) weighing 208–212 g for eight weeks at 11 °C. Synthetic astaxanthin (AX) (0.5 g/kg diet) and basal diet were used as controls. With an increase in P. rhodozyma concentration in diet, weight gain and specific growth rate exhibited an increase compared to basal diet (P < 0.05%). A significant difference was seen among the treatments but only P3 diet significantly demonstrated a better growth than AX diet (P < 0.05). Activity of antioxidant enzymes; superoxidase dismutase, glutathione peroxidase, total antioxidant activity, glutathione reductase, and catalase exhibited an enhancement in serum or liver samples of fish fed P. rhodozyma compared to basal diet (P < 0.05). Protein content in fillet of fish fed P3 diet was higher than both basal and AX diets (P < 0.05), but no significant difference was seen in contents of lipid, moisture, ash and pH values either among the treatments or between treatments and basal diet (P > 0.05). Water holding capacity and lipid loss in fillets of treatments were lower than fish fed basal diet (P < 0.05). By increasing P. rhodozyma concentration in fish diets, redness value exhibited a progressive increase, and the highest value was seen in P3 diet compared to other treatments (P < 0.05). These data show application of P. rhodozyma at 47 g/kg diet in trout could provide a better performance, antioxidant activities, and fillet pigmentation.