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Introduction

  1. Top of page
  2. Introduction
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Prebiotics are non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of health-promoting bacteria in the intestinal tract (Gibson et al., 2004). Administration of prebiotics can improve growth performance, disease resistance and gut morphology, as well as modulate the gut micro-organisms in various fish species (Salze et al., 2008; Dimitroglou et al., 2009; Ebrahimi et al., 2012). The application of prophylactic compounds such as β-glucans (βG) and mannan-oligosaccharides (MOS) improves the health of fish during their early developmental stages (Sang et al., 2009). In addition, supplementation of MOS can improve gut function by increasing the villi height, uniformity and integrity in terrestrial animals (Hooge, 2004) as well as in fish (Dimitroglou et al., 2009), which, in turn, have positive effects on nutrient digestibility (Sims et al., 2004). MOS also absorb mycotoxins found in feed ingredients commonly used in formulated diets (Pryor et al., 2003). A number of studies have demonstrated that the administration of MOS can improve the growth performance, stress resistance and gut morphology in several freshwater species (Piaget et al., 2007; Sado et al., 2008; Dimitroglou et al., 2009; Sang et al., 2009). Rutilus kutum (kutum) is one of the most commercially valuable fish species at the southern coast of the Caspian Sea (Abedi et al., 2012). Due to a sharp decline observed in the natural population, establishment of restocking centers is recognized as a solution to recover the natural stocks (Heyrati et al., 2006). Thus, the objective of this study was to determine the effect of dietary MOS on the growth performance and salinity tolerance of kutum fry.

Materials and methods

  1. Top of page
  2. Introduction
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Fish were obtained from the Voshmgir Fish-rearing Centre, Gorgan, Iran and acclimated for 1 week. After acclimation, kutum fry with an initial average weight of 740.8 ± 37.4 mg were randomly distributed in 12 fibreglass tanks (600 L) at a stocking density of 300 fish per tank. Water temperature, dissolved oxygen and pH were measured daily throughout the rearing period using a water checker (HORIBA U-10, Japan). Water temperature ranged from 25.5 to 29°C; dissolved oxygen was always above 6.1 mg L−1 and the pH was between 7.4 and 8.3. Experimental tanks were cleaned twice daily at 08.00 and 14.00 h to remove faeces and uneaten food.

The commercial diet with estimated protein levels and gross energy of 39.09% and 18.46 MJ kg−1 was provided from a local fish feed plant (Khorak Dam, Toyour and Abzian Shomal Co., Babol, Mazandaran Province, Iran). Four incremental levels (0, 1.5, 3, and 5 g kg−1) of Active-MOS were added to the basal diet to prepare four experimental diets (Table 1). Active-MOS is derived from the cell wall of yeast (Saccharomyces cerevisiae) and consists of a mannan and a glucan component.

Table 1. Percentage of ingredients and nutrient composition of Rutilus kutum fed experimental diets
Ingredient (% dry matter)Diet no.
Basal diet1.5 g kg−13 g kg−14.5 g kg−1
  1. a

    Vitamin/Mineral premix (multi vitamin and trace minerals per 500 g mixture) containing: vit. A 1000 IU, vit. D3 3000 IU, vit. E 3 mg, vit. B1 2 mg, vitamin B2 2 mg, vitamin B6 1 mg, nicotinamid 15 mg, calcium pentotenate 5 mg, vit. K3 2 mg, cu+2 3 mg, fe+2 12 mg, zn+2 15 mg, mn+2 25 mg.

  2. b

    Binder: Amet Binder (Components: Crude Protein: 71.98%, Crude Fibre: 0.9%, Ash: 17.8% Moisture: 9.55%).

  3. c

    Anti-fungal: Toxiban premix (Components: Alumino silicate, zeolite, bentonate, ammonium propionate).

  4. d

    Anti-oxidant: Butylated hydroxytoluene (BHT).

  5. e

    Means of two analyses.

Kilka fishmeal61.7   
Dextrin20.0   
Kilka fish oil4.0   
Soybean oil4.0   
Vitamin/Mineral premixa5.0   
Cellulose3.0   
Binderb2.0   
Anti fungalc0.25   
Anti-oxidantd0.05   
Nutrient composition of the experimental diet (% dry matter)e
Dry matter97.6597.2697.7497.51
Crude protein39.0438.5238.9338.88
Crude lipid17.9317.3016.8118.07
Ash9.179.069.269.58

All fish were weighed on day 1 as well as on the last day of the experiment. Experimental diets were randomly assigned to one of 12 tanks, having three replicates per diet. Fish were handfed the diets at the rate of 7–12% of biomass, three times per day (8.00, 14.00, and 18.00 h). The experiment lasted for 8 weeks, and all fish were weighed on day 56, the final day. Beforehand, 30 fish were randomly selected from each tank and distributed to two other tanks for salinity stress tests. Two salinity levels (10.8 and 13.1 ppt) were selected based on the fingerling release site and natural habitat of kutum. The fish were kept in tanks of saline water for 48 h. For the lactic acid bacteria counts, six fish were collected from each treatment and their intestine samples tested for bacteria counts. The intestines were removed under sterile conditions. All samples were diluted using sterilized normal saline solution (0.85% NaCl w/v) and then placed onto MRS (DeMan, Rogosa and Sharpe) plates for isolation and total bacteria counts (Peter and Sneath, 1986).

Statistical analysis

Data are presented as the means of each treatment ± SD. All data were checked for normality after transformation (ASIN). One-way anova was used to determine the effects of Active-MOS on fish performance, stress test and bacterial number. The means were compared by a Tukey's post hoc test. For all statistical analyses, each tank was considered as an experimental unit. Within 48 h survival measurements were considered as repetitive, thus the effect of Active-MOS on survival was by repeated measurement analysis.

Results

  1. Top of page
  2. Introduction
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The inclusion of different levels of Active-MOS did not influence growth-related parameters or the survival rate of kutum during the 8-week experiment (P > 0.05; Table 2). Similar to growth parameters, fish survival was not significantly changed at either salinity level by MOS supplementation. The salinity stress test showed that 48 h measurements of the survival rate were similar for both salinity levels (P > 0.05), although there was a trend toward survival of larger fish for those fed 1.5 g kg−1 Active-MOS (Figs 1 and 2). The intestinal lactic acid bacteria measurement demonstrated that the inclusion of a dietary prebiotic did not affect the lactic acid bacteria level of R. kutum (Fig. 3).

Table 2. Growth performance in kutum feeding on different levels of Active-MOS over 56 days experimental period
Growth parametersDiet
Basal diet1.5 g kg−13 g kg−14.5 g kg−1
  1. Data are presented as mean ± SD.

Initial body weight (mg)764 ± 6.9734 ± 52.6722.3 ± 39746.7 ± 44
Final body weight (mg)1605.3 ± 95.91625 ± 64.71529.7 ± 89.91497.7 ± 28.4
Weight gain (mg)110 ± 10.8122.1 ± 28.2107.7 ± 11.6105 ± 13.8
Specific growth rate (%/day)1.32 ± 0.091.42 ± 0.221.3 ± 0.091.28 ± 0.11
Feed conversion rate5.3 ± 0.35.1 ± 1.15.6 ± 0.55.8 ± 0.2
Survival (%)91.1 ± 5.3591.4 ± 5.3889.9 ± 1.5390.8 ± 5.06
image

Figure 1. Survival at the end of the experiment with kutum, Rutilus kutum, fry fed diets containing different levels of Active-MOS during a 48-h salinity stress test (10.8 ppt) (N = 30)

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image

Figure 2. Survival at the end of the experiment of R. kutum fry fed diets containing different levels of Active-MOS during a 48-h salinity stress test (13.1 ppt) (N = 30)

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image

Figure 3. Intestinal lactic acid bacteria levels [log colony forming units (CFU g−1) intestine] of R. kutum fry fed diets containing different levels of Active-MOS Vertical axis: total count of lactic acid bacteria (Log cfu g−1)

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Discussion

  1. Top of page
  2. Introduction
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The results of the current study indicate that dietary supplementation of Active-MOS did not affect fish performance, stress resistance, or the lactic acid bacteria count in kutum fry. The findings are similar to those of Pryor et al. (2003) and Mahious et al. (2006), who observed a similar growth performance in Gulf sturgeon and turbot larvae that were fed prebiotic diets. Our results are in contrast to a large number of previous studies that showed positive effects of different dietary prebiotics on fish performance, feed efficiency and immune response of aquatic animals (Burrells et al., 2001; Pausen et al., 2001; Bridle et al., 2005). The exact reason for such contradictory results is not yet clear. The contradictory results obtained from prebiotic studies on fish performance may be related to species, dosage levels, fermentability of the prebiotics, and the different intestinal morphology and microbiota (Hoseinifar et al., 2010). Further work is necessary that focuses on the bacteria community using different types and levels of carbohydrates under different environmental conditions in order to fully assess any possible effects on fish performance caused by those parameters.

A trend toward a greater survival rate of fish fed 1.5 Active-MOS during a 48 h salinity test may indicate that prebiotic supplementation can control mortality when kutum fry are exposed to a stressful situation. Similarly, inclusion of mananoligosaccharides improved larval stress tolerance in white seabream (Diplodus sargus) (Dimitroglou et al., 2010).

More basic research focusing on the mechanisms through which prebiotics may have an affect is needed to verify the reason why similar prebiotics lead to different results. Based on the findings of this study, we do not suggest the supplementation of Active-MOS for feeding Rutilus kutum fry.

Acknowledgements

  1. Top of page
  2. Introduction
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

This work was carried out at the Voshmgir Centre, fish rearing centre, Gorgan, Iran. The authors would like to thank the experts of the centre. This project is being supported logistically by the Aria Company.

References

  1. Top of page
  2. Introduction
  3. Materials and methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
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