Practical Methods Of Improving Health & Performance Status In Mediterranean Aquaculture Species

Digital re-print - January | February 2009 Feature: Mediterranean Feature title: Practical methods of improving health & performance status in Mediterranean aquaculture species International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2009 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

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Mediterranean

Mediterranean

maximize the growth potential of the species.

Improving gastrointestinal performance and immune status

Practical methods of improving health & performance status in Mediterranean aquaculture species by Dr Elizabeth Sweetman, Ecomarine Ltd, Livadi, 28200 Lixouri, Cephalonia, Greece and Dr Ioannis Nengas, Hellenic Centre for Marine Research, Institute of Aquaculture, Agios Kosmas, 16777 Athens, Greece Gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) are two of the most important marine fish species farmed in the Mediterranean region. Currently approximately 100,000 tonnes of sea bass and 120,000 tonnes of sea bream are produced annually in aquaculture facilities, which are typically net pen cages although some pond and tank culture does occur.

O

ften in industrial scale farms unfavourable environmental conditions (oxygen levels, pH, water quality, temperature fluctuations), sub-optimal growth conditions (inadequate nutrition, overcrowding, overfeeding) and the reality of practical husbandry practices combine to result in the development of stressful situations. These ultimately express themselves in poor performance, suppression of immune defence mechanisms and variable product quality (Bonga, 1997; Wedemeyer, 1997; Pickering 1998). All this combines to make the farmed fish - Gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) - more vulnerable to ubiquitous opportunistic bacterial and viral pathogens and parasitic infections.

The industry reports that average mortalities from juvenile to a market size of 330g are about 10 percent for gilthead sea bream and up to 20 percent for sea bass. Many of these losses can be attributed to the development of diseases, which negatively impact profitability, especially so at times where profit margins are tight. Constraints in the market prices of sea bream and sea bass have led the aquaculture industry to consider many approaches to minimising losses, improving production and reducing costs. It is possible to protect against certain diseases with vaccination strategies but only a limited number are available for commercial use. Restrictions on the use and variety of therapeutics available to the industry, increasing consumer concerns and social considerations have led the industry to consider more environmentally friendly approaches to disease control (Hansen and

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Olafsen 1999 Verscheure et al 2000). Good management practices and sanitary prevention measures are recommended including the integrated use of vaccines and health promotional nutritional supplementation that help prevent infection and strengthens immune defence mechanisms. (IUCN 2007). An important area of research is the formulation of optimal diets that meet the specific requirements of each fish species and each developmental stage through the productive cycle. Mineral nutrition in aquafeeds is important for many reasons such as skeletal formation, maintenance of colloidal systems regulation of acid-base equilibrium and for biological compounds such as hormones and enzymes (Lall 2002). Even although the requirements for these micronutrients has been determined for several species no reliable data is available for most marine cultured fish,

Modern agricultural farm practises place heavy emphasis on the quality and performance of young animals. It is considered vital that Control the best possible start is given to the young, as an animal never performs best after a bad start. Similarly in aquaculture just as poor larval fish survival rates will limit production so will poor juvenile quality. Juvenile quality can be difficult to assess but the industry considers parameters such as growth rate, mortality and susceptibility to disease, occurrence of fish with skeletal deformities or large size disperBio Mos sions and differing stress sensitivities as indicators of quality. Figure 1: Microvilli from white sea bream larvae The importance of the fed with enriched Artemia with and without piscine gastrointestinal Bio-Mos supplementation. In the control group the microvilli are not continuous and they tract and its mucosa as contain gaps (G) and are broken (BP) in place. a defensive barrier to The scale bar illustrates a length of 2μm pathogen attack, its role as a major endocrine and osmoregulatory organ and its function as a especially the Mediterranean species like mechanism for nutrient uptake makes the sea bream and sea bass. U n d e r stress conditions dietary nutrient, trace mineral and vitamin requirements often change and consideration, therefore, has to be given to adequately compensate for this, combat the negative effects of stress and

integrity of this system vital to the health, performance and therefore quality status of the fish. Mannan oligosaccharides have been shown to modulate the gastrointestinal integrity of marine fin fish. Dimitroglou et al, 2007 showed that the inclusion of a specific mannan oligosaccharide, derived from yeast cell wall material, Bio-Mos® (Alltech Inc, USA) in the diets of several marine species including sea bream improved the gut morphology by increasing the microvilli density in both the anterior and posterior gut regions and significantly increasing the microvilli length. These changes in the gut morphology indicated that the absorptive surface of the gut had been improved and that a better absorptive capacity appeared to be possible. These improvements in gut morphology have also been noted in the larval stages of white sea bream (Diplodus sargus)(Dimitroglou, 2004) and cobia (Rachycentron candum)(Salze et al, 2008). Larval quality was significantly improved by adding Bio-Mos through the enrichment media of the Artemia. In these experiments, villi morphology was unaffected, however, microvilli condition was improved and damaged areas of the gut reduced with Bio-Mos supplementation. Similarly, Daniels et al (2005) demonstrated that adding Bio-Mos to the artemia enrichment media improved survival rate in larval lobster (Hommarus gammarus) to stage IV and further noted that Vibrio sp. levels were reduced in the Artemia culture medium. One of the key benefits of this specific mannan oligosaccharide is its ability to bind

Figure 2: The inclusion of Bio-Mos in sea bass juvenile diets improved the head kidney leukocytes phagocytic activity and bactericidal activity

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Mediterranean or agglutinate a number of strains of bacteria known to cause disease in shrimp and fish thereby preventing colonization of the gut and subsequent infection. Dimitroglou et al, 2007 demonstrated that Bio-Mos significantly reduced the bacterial load in the gut of both rainbow trout and sea

cent and produced a better specific growth rate at low fish densities. The incorporation of Bio-Mos also resulted in improvement of the hepatocyte morphology with more regularly shaped hepatocytes and less hepatocytes with displaced nuclei to the cellular periphery. The activities of lipogenic enzymes in the liver were significantly reduced at the different incorporation levels of Bio-Mos. This development work has shown interesting new trends indicating the possibility of interaction with nutrient uptake mechanisms as Figure 3: The number of cells secreting acid mucins in indicated by the posterior gut significantly increased with Bio-Mos the reduced supplementation (P<0.05). (Torrecillas et al, 2008) liver fat deposition and the bream by reducing the total aerobically improved hepatic composition that may be cultivated bacteria. an indicator of better utilization of dietary In sea bass juveniles Torrecillas et al. nutrients. (2007a & b) has reported that the dietary The immune function was also improved incorporation of Bio-Mos significantly and the immune parameters, phagocytic increased growth, by approximately 10 peractivity of leucocytes and the bacterial activity of the sera in the Bio-Mos fed groups showed a statistically significant improved dose response when compared to the control group. Disease resistance to bacterial infection, both by cohabitative challenge and by direct inoculation in the gut, were enhanced when Bio-Mos was Figure 4: Chemiluminescence activity in sea bream as a incorporated function of incorporation of organic iron (Control – no organic iron, B–ppm Bioplex Iron, F-ppm Ferous iron) in the diets. In cohabitation 16 | InternatIonal AquAFeed | January-February 09

trials the presence of Vibrio alginolyticus on the head kidney of sea bass was 33 percent for the control group and eight percent and 0 percent respectively for the 0.2 percent and 0.4 percent Bio-Mos fed groups. Torrecillas et al (2008) reported that in sea bass fed two months of Bio-Mos supplementation the number of cells secreting acid mucins in the posterior gut was significantly increased. The increase in mucus secretion with its anti-adhesive properties could be directly related to the decrease in the number of infected fish in disease challenge trials reported previously. (Torrecilas et al 2007a,b) In studies by Dimitroglou at the University of Plymouth improvements in the blood health parameters of gilthead sea bream were observed with the dietary inclusion of Bio-Mos. A reduction in the monocytes/macrophages in blood circulation was observed and that together with the increase in the number of lymphocytes in the Bio-Mos supplementation groups may be responsible for the reduction of the haemolytic complement activity (ACH50). Increased numbers of lymphocytes in the blood system indicate that a faster immunological response may occur in the event of an infection.

Improving health status through mineral nutrition Iron is one of the most importantly recognised trace minerals for fish health and production. Iron (Fe) plays a key role in oxygen transport in the blood, has an active role in oxidation/reduction reactions and electron transport associated with cellular respiration. Iron deficiency can cause anaemia or even low haemoglobin levels in fish and in certain conditions iron toxicity resulting in reduced growth, poor feed utilization, feed refusal, increased mortality and histopathological damage to liver cells (Lall 2002, Halver & Hardy 2002). According to Watanabe et al. (1997), the major factor that can influence iron absorption is the relative proportion of organic and inorganic forms of the metal in the diet, organic forms being more efficiently absorbed when compared to inorganic forms. When the effect of an organic iron supplementation (Bioplex Iron®, Alltech Inc, USA) was studied in healthy sea bream no effect was observed in the haematocrit PREVIOUS PAGE

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Mediterranean or haemoglobin levels between the control and the organically supplemented diets. However the red blood cell counts was affected by the different levels of the supplemented iron. Chemiluminescence activity showed an improved immune response in relationship

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percent have been observed and the effect of this parasite can add an additional two months to the growth cycle. To counteract the anaemia 200ppm Bioplex Iron was added to the diet and mortalities were reduced to <2 percent of the population, haematocrit levels increased to normal levels of approximately 35 percent and growth rates increased. This provides a practical tool for treating the symptoms of infected populations of sea bream and reducing the negative commercial impacts associated with the parasitic infection. These practical and functional nutritional tools provide opportunity for producers to combat a number of naturally occurring specific and nonspecific diseases and their symptoms by improving the general health status of fish stocks. The promotion of improved fish health status through prophylactic measures such as these are environmentally sound, address the realities of commercial production and are welcomed by the modern consumer.

Acknowledgements

Figure 5: Microcotyle sp.

to the incorporation of organic iron at a level of 100-150 ppm. At this level the response was significantly higher compared to the ferrous form. Fish fed the ferrous form at 200ppm demonstrated significantly lower immune response compared to the 100ppm and 150ppm Bioplex Iron fed groups. In Greece sea bream juveniles of between 20 to 50g are susceptible, in the Spring, to infection with a gill parasite microcotyle sp. In challenged juveniles this monogenean parasite causes anaemia and mortalities can reach up to 15 percent of the population. Low haematocrit levels of approximately 10

To Arkadios Dimitroglou, University of Plymouth, UK and Silvia Torrecillas, ULPCG, Gran Canaria, Spain for their contribution to this article.

References Bonga S.E.W. (1997) The stress response in fish. Physiol. Rev. 77 (3), 591-625. Daniels C. (2005) Effects of Bio-Mos on the growth of lobster, Homarus gammarus larvae. In: Nutrition and Biotechnology in the Feed and Food Industries: Alltech’s 21st Annual Symposium (Suppl. 1 - Abstracts of posters presented) Lexington, KY, USA. Dimitroglou A. (2004) The role of mannan oligosaccharide on the development of white sea bream (Diplodus sargus) larvae. Thesis submitted to the University of Plymouth for the degree of MRes Applied Fish Biology. Dimitroglou A., Davies S., Moate R., Spring P. & 18 | InternatIonal AquAFeed | January-February 09

Sweetman J. (2007) The beneficial effect of BioMos on gut integrity and enhancement of fish health. Presented at Alltech’s Technical Seminar Series held in Dublin, November 2007. Halver J.H. & Hardy R.W. (2002) Fish Nutrition. Academic Press. Hansen G.H. & Olafsen J.A. (1999) Bacterial interactions in early life stages of marine cold water fish. Microb. Ecol. 38, 1-26. Guide for the Sustainable Development of Mediterranean Aquaculture, Interactions between Aquaculture and the environment, (2007) IUCN, Gland, Switzerland and Maliga, Spain, 110 pages ISBN 97884-491-0767-2. Lall S.P., (2002), The Minerals. In: Fish Nutrition (ed. by Halver J.H. & Hardy R.W) Academic Press, pp260-366. Pickering A.D. (1998) Stress responses of farmed fish. In: Biology of farmed fish (ed. by K.D. Black & A.D. Pickering AD), CRC Press, Boca Raton, pp 222-255. Salze G., Mclean E., Schwarz M.H. & Craig S.R. (2008) Dietary mannan oligosaccharide enhances salinity tolerance and gut development of larval cobia. Aquaculture 274, 148-152. Torrecillas S., Makol A., Caballero M.J., Montero D., Robaina L., Real F., Sweetman J., Tort L. & Izquierdo M.S. (2007a) Immune stimulation and improved infection resistance in European sea bass (Dicentrarchus labrax) fed mannan oligosaccharides. Fish & Shellfish Immun. 23, 969-981. Torrecillas S., Caballero M.J., Sweetman J., Makol A. & Izquierdo M.S. (2007b) Effects of feeding BioMos on European sea bass (Dicentrarchus labrax) juvenile culture. Presented at Alltech’s Technical Seminar Series held in Dublin, November 2007. Torrecillas S., Makol A. Caballero M.J. Montero D. Sweetman J. and Izquierdo M.S. (2008) Enhanced nutrient utilization and bacterial infection resistance in European sea bass (Dicentrarchus labrax) fed mannan oligosaccharides. Poster presented at the XIII International Symposium on Fish Nutrition and Feeding, Brazil 2008. Verschuere L., Rombaur G., Sorgeloos P. & Verstraete W. (2000) Probiotic bacteria as biological control agents in aquaculture. Microbiol. Mol. Biol. Rev. 64, 655-671. Watanabe T., Kiron V. & Satoh S. (1997) Trace minerals in fish nutrition. Aquaculture 151, 185207. Wedemeyer G.A. (1997) Effects of rearing conditions on the health and physiological quality of fish in intensive culture. In: Fish stress and health in aquaculture. (eds G.K. Iwama, A.D. Pickering, J.P. Sumpter and C.B. Schreck CB). Society for experimental biology seminar series 62. Cambridge University Press, Cambridge, pp35-71. PREVIOUS PAGE

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