Improving growth performance and health status of aquaculture stocks in Europe through the use of Bio-Mos

The financial success of an aquaculture species is dependent on an advanced understanding of the biology, nutrition and environmental management of the production cycle. Optimal growth and performance can be affected by disease outbreaks and physiological and immune status.

Stress and environmental conditions are closely interlinked (Varsamos et al., 2006) and can lead to reduced performance and susceptibility to disease. Short periods of subclinical challenge with opportunistic pathogens can affect productivity and disrupt gut integrity, leading to poor nutrient uptake and unbalanced gut microflora.

Prophylactic strategies aimed at the reduction of stress and the exposure of fish to potential pathogens include strict operational management and biosecurity programmes. Vaccination, where pathogen-specific vaccines are available, is an effective tool against disease.

However the development of the immune cognizance and the availability of vaccines do not cover all the practical requirements of the farmer during the life cycle of the animal. Focus has shifted to nutritional strategies that improve fish health status, help optimize performance, improve stress and disease resistance and improve gut morphology and efficiency.

Bio-Mos® is a mannan oligosaccharide derived from the outer cell wall of a specific strain of Saccharomyces cerevisiae using a proprietary process developed by Alltech Inc. Its use in terrestrial animals is well documented, however it is only recently that its effectiveness in aquaculture has been established. Improvements in the performance and health status of several species of fish are being seen. This paper documents recent trial work carried out with trout, carp, catfish, tilapia, sea bass, sea bream, sole and salmon.


Effect of Bio-Mos® on performance parameters

The two primary freshwater fish species produced in European waters are trout and carp. Trout production is spread throughout Europe and more than 300,000 tonnes were produced in 2005. Two species of trout are cultured; rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) in both intensive and extensive systems.

Although ranking second in production in Europe, carp has the longest history in aquaculture and worldwide makes the largest contribution to providing a food fish. The greatest part of the European carp production is in Central and Eastern Europe (Germany, Hungary, Poland, Austria, Czech Republic, Bulgaria, Romania, Russia, Belarus, etc.), where it is produced in ponds using traditional extensive or semi-intensive techniques.

In the European region, excluding Russia and its satellite countries, some 70,000 tonnes of carp are produced from approximately 300,000 Ha of ponds. Productivity is relatively low, from 200-300 kg/Ha.

The common carp (Cyprinus carpio L.) is the main species cultured, and in extensive systems the diets for carp are generally pelleted with lower protein and fat levels (30% protein and 7% lipid) and with a high component of grains. High energy extruded diets (up to 56% protein and 15% lipid) are generally used in the highly intensive indoor recirculation systems seen in some European countries.

A recent trend however is the use of extruded floating diets fed into floating polyethylene circular confinement areas in large ponds. This trend is an important development when considering feed efficiency and productivity.


Performance responses to Bio-Mos®

CARP

Controlled experiments took place at the University of Trakia in Bulgaria with carp (Staykov et al., 2005c) in which 0.2% Bio-Mos® was incorporated into a standard commercial extruded diet (23.5% protein and 5.4% lipid).

From a start weight of approximately 140 g, fish given Bio-Mos® grew to an average weight of 480 g vs. 430 g in controls, an 11.6% higher weight gain (P<0.001). Feed conversion ratios (FCR) were improved with Bio-Mos® (1.69 vs. 2.05 in controls), by 17.6% (P<0.01). Lower mortalities were also observed in the Bio-Mos®-fed fish (1.92% vs. 3.59% for the control, P<0.001).

Juvenile carp reared in tanks at the University of Osijek in Croatia showed similar improvements in weight gain in response to Bio-Mos® (Culjak et al., 2006). The diet used in these trials was 39.91% crude protein and 4.51% lipid; and Bio-Mos® was added at 0.6%.

The fish grew from an average weight of 5.28 g to 31.23 g in controls vs. 38.73 g in the Bio- Mos® treatment, a 24% higher weight gain (P<0.01). Bio-Mos® improved FCR from 2.06 to 1.60 (P<0.05); and mortality from 50.0 to 16.7% (P<0.01).


TROUT

Similar trials were conducted with Rainbow trout (Staykov et al., 2005 a, b) with a 0.2% Bio-Mos® inclusion rate in commercial feeds resulting in increased average weights of 13.7% (P<0.001) in fish grown from 30 g to just under 100 g. Mortalities and FCRs were significantly improved in resonse to Bio-Mos®. FCR decreased from 0.91 in controls to 0.83 in trout given Bio-Mos® (P<0.05). Mortalities decreased from 1.68% in controls to 0.58% in fish given Bio-Mos® (P<0.001).

Fish grown from 100 g to approximately 310 g also showed improved performance. The growth in trout fed Bio-Mos® was 10% higher than the control (P<0.01) and the FCR decreased by 11.2% to 1.07 (P<0.001) with Bio-Mos® addition. Mortalities also decreased from 5 to 2.95%, a reduction of 41% (P<0.001).


EUROPEAN CATFISH

The addition of Bio-Mos® to other freshwater species such as European catfish (Silurus glanis) juveniles (Bogut et al., 2006) has shown similar improvements in growth from 22 to 76 g in the control groups and 83 g in the Bio-Mos® groups, a 9.7% higher average body weight (P<0.01). The FCR was also lower by 11.6% (P<0.01) and mortality decreased from 28.33 to 16.67% (P<0.01).

These data support findings of Hanley et al. (1995) who also demonstrated that hybrid red tilapia juveniles fed 0.6% Aqua-Mos™ (Alltech Inc.) in their hatchery diets had a 22.5% improved survival with a 27.2% increase in weight gain.


SEA BASS

In the Mediterranean marine finfish industry nearly 900 million juveniles of sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) are put into sea cages and pond systems annually. In Turkey, Bio-Mos® is being used systematically in the feed industry as numerous farmers report improved growth, survival and improved feed conversion rates for the sea bass and sea bream industry. Ege University (Hossu et al., 2005a,b) showed that Bio- Mos® improved growth performance and decreased mortality in sea bream.

A recent controlled experimental programme carried out at the University of Las Palmas of Gran Canaria in Spain with 35 g sea bass (Dicentrarchus labrax) juveniles studied the effect of two inclusion rates of Bio-Mos® (0.2 and 0.4%) on a number of growth, immunological, histological and biochemical characteristics (Torrecillas et al., 2006) (Figure 1).

Growth in terms of final body weight, specific growth rate (SGR) and relative growth significantly increased by about 10% (P<0.05) in sea bass fed Bio-Mos® at both inclusion rates. Bio-Mos® increased feed intake compared to the control, however at the end of the experimental period both treatments had similar FCRs.





Figure 1. Effect of dietary Bio-Mos® level on growth, specific growth rate and feed conversion efficiency of European sea bass.



The whole body, muscle and liver biochemical composition as well as gut and liver histological structure were examined and no significant differences were found in the fish whole body, muscle or liver proximate compositions. Histological features at the optical microscope level showed no differences between the guts of fish fed the different diets although studies at the electronic level are still to be completed.

Craig and McLean (2003) found that the incorporation of Bio-Mos® in Nile tilapia (Oreochromis niloticus) at various levels from 0.25 to 2% Bio-Mos® resulted in a leaner fillet than observed in the control animals. However, Bio-Mos® did not reduce hepatic lipid accumulation in this experiment.

Hepatocytes of sea bass fed the control diet showed high lipid vacuolization with nuclei being displaced to the edge of the cell. In contrast, fish fed Bio-Mos® showed a gradual reduction in the vacuolization, denoting a better utilization of dietary nutrients (Figure 2). Biochemical analysis of the liver revealed a reduced fat content (-5%), less humidity (-3%) and a higher protein content (+2%) with Bio-Mos® supplementation.




Figure 2. Effect of dietary Bio-Mos® level on vacuolization of sea bass hepatocytes.



The improved growth performance observed with the ULPGC trial is also seen in the early results from ongoing research with salmon in Norway, in which a strong trend for improved growth rate was observed. Thermal growth coefficient increased from approximately 2.1 in the control treatments to 2.3 in the Bio-Mos®-treated groups.

Specific growth rates increased from 0.58 to 0.62 (P<0.13), respectively.


Bio-Mos® effects on gut histology

Investigators at the University of Plymouth have been investigating the effects of Bio- Mos® inclusion in aquaculture feeds on gut morphology. Incorporation of Bio-Mos® into the live feed Artemia has shown improvements in growth and improved survival from 5-13% for the control and 28.4% in Bio-Mos®-treated lobster larvae to stage IV (Daniels, 2005).

Similar work with white sea bream (Diplodus sargus) (Dimitroglou et al., 2005) showed improved developmental rate as indicated by length increment and improved larval quality through better resistance to handling and salinity stress. Electron microscope studies of the intestine showed improved condition of the brush border microvilli through more uniform structures without gaps or broken parts.

Gut integrity of sole (Solea senegalensis) was examined in an industrial trial in Spain. Bio-Mos® improved anterior gut morphology and electron microscopy showed more dense and more complex microvilli structures together with more regular and deeper intestinal foldings (villi) in the Bio-Mos®-treated fish. In addition, fewer damaged areas were noticed at the electron microscopic level with the Bio-Mos®-treated fish (Figures 3 and 4).




Figure 3. Improved gut villi morphology in Diplodus sargus (Dimitroglou, in press).






Figure 4. Effect of Bio-Mos® on anterior gut morphology.



Effect of Bio-Mos® on health status of fish stocks

The immune status of trout and carp has been investigated in the previously mentioned trials using standard blood sera methods including bactericidal activity, antibody titres, lysozyme concentration (Lie, 1985), alternative pathway of complement activity (APCA) (Sotirov, 1986) and classical pathway of complement activation (CPCA) (Stelzar and Stein, 1971). The results shown in Table 1 indicate that the immune status was improved in carp and trout in response to Bio-Mos®.


Table 1. Effects of Bio-Mos® on immune system indicators in carp and trout.


**P<0.001
*P<0.05



Improved immune status and disease resistance to cohabitant and inoculative challenge tests with the pathogen Vibrio alginolyticus were observed in the sea bass juvenile trials at ULPGC.

The phagocytic index was monitored at day 36 of the trial and increased (P<0.05) with the inclusion of 0.4% Bio-Mos®. The phagocytic activity of the head kidney macrophages reached 32.4% in the 0.4% Bio-Mos® treatment and 26.9% in the 0.2% Bio-Mos® treatment compared with 23.8% in controls (Figure 5).

Respiratory burst activities of circulating neutrophils were greater (P<0.05) in the fish fed Bio- Mos® at 0.2% and 0.4% inclusion rates.





Figure 5. Effect of Bio-Mos® inclusion on disease resistance of European sea bass.



After the feeding trial, sea bass had reached approximately 100 g average weight and specimens of all treatments were exposed to a cohabitation system for 21 days with specimens infected with Vibrio alginolyticus in a ratio of 3:1. The spread of infection was monitored by the recovery of the pathogen from the head kidney of the fish.

After this challenge test, 33% of the controls were infected, compared with 8.3% on the 0.2% treatment and none on the 0.4% Bio-Mos ® treatment. New fish in this study were directly infected by gut canalisation and 48 hr post-inoculation 20% of the total number of the control fish were infected, twice as many as in fish fed Bio-Mos®.


Discussion

The interactions among intestinal microflora, gut morphology, the immune system and nutrient uptake has a major influence on animal health and performance. Non-specific enhancement of disease resistance is particularly relevant in farmed fish as they are vulnerable to ubiquitous opportunistic bacterial pathogens that can take advantage of fish stocks when stressed.

The results discussed in this paper clearly demonstrate the association of improved growth and performance, gut health, immune status and resistance to disease in fish fed Bio-Mos®. Improved hepatocyte condition may well be an indicator of better utilization of dietary nutrients; and this in association with improved gut morphology may suggest reasons for better growth and performance.


References

Bogut, I., Z. Milakovic, J. Pavlicevic and D. Petrovic. 2006. Effect of Bio-Mos® on performance and health of European catfish. In press.

Culjak, V., i. Bogut, E. Has-Schon, Z. Milakovic and K. Canecki. 2006. Effect of Bio- Mos® on performance and health of juvenile carp. In press.

Craig, S.R. and E. McLean. 2003. The effect of dietary inclusion of Bio-Mos® upon performance characteristics of Nile tilapia. In: Biotechnology in the Feed Industry: Proceedings of Alltech’s 19th Annual Symposium (Suppl. 1) (Abstracts of posters presented). Lexington, KY, May 23-35.

Daniels, C. 2005. Effects of Bio-Mos® on the growth of lobster, Homarus gammarus larvae In: Nutritional Biotechnology in the Feed & Food Industries: Proceedings of Alltech’s 21st Annual Symposium (Suppl. 1) (Abstracts of posters presented). Lexington, KY, May 23-25.

Dimitroglou, A., S. Davies, P. Divanach and S. Chatzifotis. 2005. The role of mannan oligosaccharide in gut development of white sea bream, Diplodus sargus. In: Nutritional Biotechnology in the Feed & Food Industries: Proceedings of Alltech’s 21st Annual Symposium (Suppl. 1) (Abstracts of posters presented). Lexington, KY, May 23-25.

Hanley, F., H. Brown and J. Carberry. 1995. First observations on the effects of mannan oligosaccharide added to the hatchery diets for warmwater Hybrid Red Tilapia. In: Nutritional Biotechnology in the Feed & Food Industries: Proceedings of Alltech’s 11th Annual Symposium (Suppl. 1) (Abstracts of posters presented). Lexington, KY, May.

Hossu, B., S. Salnur and N. Gultepe. 2005a. The effects of yeast derivatives (Bio-Mos®) on growth of Gilthead sea bream, Sparus aurata. In: Nutritional Biotechnology in the Feed & Food Industries: Proceedings of Alltech’s 21st Annual Symposium (Suppl. 1) (Abstracts of posters presented). Lexington, KY, May 23-25.

Hossu, B., S. Salnur and N. Gultepe. 2005b. The effects of yeast derivatives (Bio-Mos®) on digestibility of Gilthead sea bream, Sparus aurata. In: Nutritional Biotechnology in the Feed & Food Industries: Proceedings of Alltech’s 21st Annual Symposium (Suppl. 1) (Abstracts of posters presented). Lexington, KY, May 23-25.

Lie, O. 1985. Improved agar plate assays of bovine lysozyme and haemolytic complement activity. In: Markers of Resistance to Infection in Dairy Cattle. Dissertation, Oslo, Norway, National Veterinary Institute 5:1-12.

Sotirov, L.K. 1986. Method for determination of the alternative pathway of complement activation in some animals and man. In: Fourth Scientific Conference of Agriculture. Stara Zagora, pp. 1-10.

Staykov, Y., S. Denev and P. Spring. 2005a. The effects of mannan oligosaccharide (Bio- Mos®) on the growth rate and immune function of rainbow trout (Salmo gairdneri irideus G.) grown in net cages. In: Lessons from the Past to Optimise the Future (B. Howell and R. Flos, eds). European Aquaculture Society, Special Publication No 35, June 2005, pp. 427-432.

Staykov, Y., S. Denev and P. Spring. 2005b. The effects of mannan oligosaccharide (Bio- Mos®) on the growth rate and immune function of rainbow trout (Salmo gairdneri irideus G.) grown in raceways. In: Lessons from the Past to Optimise the Future (B. Howell and R. Flos, eds). European Aquaculture Society, Special Publication No. 35, June 2005, pp. 429-430.

Staykov, Y., S. Denev and P. Spring. 2005c. Influence of dietary mannan oligosaccharides (Bio-Mos®) on growth rate and immune function of common carp (Cyprinus carpio L). In: Lessons from the Past to Optimise the Future (B. Howell and R. Flos, eds). European Aquaculture Society, Special Publication No 35, June 2005, pp. 431-432.

Stelzar, A. and G. Stein. 1971. Moglichkikten zur hamolytishchen Aktivitatsmessung von Gesamtkomplement Theoretische Grundlangen und methodische Hinweise.

Wissenschaftliche Zeitschrift der Friedrich Schiler Universitat Jena. Mathematisch Naturwissenschaftlische Reihe 20, Jg H6:933-941.

Torrecillas, S. and M.S. Izquierdo. 2006. The effect of Bio-Mos® on European sea bass (Dicentrarchus labrax) juveniles. In press.

Varsamos, S., G. Flik, J.F. Pepin, S.E. Wendelaar Bonga and G. Breuil. 2006. Husbandry stress during early life stages affects the stress response and health status of juvenile sea bass, Dicentrarchus labrax. Fish Shellfish Immun. 20:83-96.