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Natural Feed Additives to Reduce the Impact from Parasites on Marine Fish Farming in the Mediterranean Region

New diseases emerge every year which brings new actors into scene. Turkish aquaculture is therefore continuously and quickly running updates and new protocols on farm management aiming to reduce disease pressure while reducing production costs. The fast speed of the industry makes it prone to failures in the development and application of disease prevention strategies.

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Dr. Waldo G. Nuez-Ortín- Doctor of Veterinary – Nutriad International – Belgium
Mercé Isern-Subich (DVM) – Doctor of Veterinary – Nutriad International – Belgium

Marine aquaculture in Turkey is a fast-growing industry. With the expansion and intensification of the production, disease is becoming an important constrain for the profitability of the industry.

In open sea farming, disease is not easy to deal with. Presence of multiple primary pathogenic pathogens combined with multiple opportunistic are testing the capacity of the industry to efficiently adapt health prevention strategies. Application of knowledge developed in other Mediterranean regions to target same pathogenic species is not always successful since the impact of disease is specific to region characteristics, such as water quality, degree of intensification or farming concentration among others. Furthermore, new diseases emerge every year which brings new actors into scene (e.g. Enterospora nucleophila, Aeromonas veronii, etc..). Turkish aquaculture is therefore continuously and quickly running updates and new protocols on farm management aiming to reduce disease pressure while reducing production costs. The fast speed of the industry makes it prone to failures in the development and application of disease prevention strategies. Nutriad is committed to support the rapid expansion of industry through specialized services and field experienced professionals. Our aqua experts have regional view and farm-to-fork insight in the aquaculture food chain and provide world-wide expertise in practical disease prevention and treatment.

Major parasitic diseases described in Turkey are caused by species that belong to the myxosporeans and monogeneans. Myxosporeans proliferate in different target organ and tissues and monogeneans are obligatory parasites of the gills and skin of marine fishes. Environmental conditions that approach or exceed animals’ physiological tolerances, such as temperature or salinity, are thought to contribute to outbreaks and progression of these parasitic diseases. There are neither vaccines nor effective prescription medicines for these parasites and their control measures are limited to avoidance of risk factors, early diagnosis, and good farm management practices. Nutriad offers solutions to prevent and minimize the impact of the infection through the use of feed additives with functional properties including antiparasitic and immunoregulatory. Nutriad´s health promoting feed additives are based on combinations of synergetic natural compounds, such as phytobiotics, immune-stimulants and organic acids that can work through multiple mechanisms against a broad spectrum of parasites. We continuously invest significant efforts to increase our understanding of the impact of different combinations on specific fish-parasite interactions and therefore to establish effective dose-responses and prevention strategies that are practical to the producer.

One of our recent projects has been the use of model parasite species to evaluate the disease prevention potential of functional feed additives against myxosporeans in marine fish. With this aim, we used Enteromyxum leei, a myxosporean almost exclusively found in intestine and with spontaneous direct fish-to-fish transmission (Palenzulea et al. 2017. Sanacore®GM, a functional feed additive with broad spectrum antiparasitic activity, was included into a commercial feed formula at two different dosages (0.2% – low – and 0.4% – high -) and fed to gilthead seabream fingerlings (~13 g) prior to an experimental infection with E. leei. After five weeks on the experimental feeds, fish were inoculated with a homogenate from intestinal scrapings of infected donor fish via the anal route (Estensoro et al. 2010), while an additional group of fish fed the basal experimental feed received the same volume of PBS without parasites. The experimental challenge with E. leei effectively infected fish and induced the clinical signs of enteromyxosis. The evolution of feed intake and biometrical data along ten weeks post-infection clearly evidenced the clinical effect of the infection in challenged groups (Figure 1). Fish challenged with the parasite suffered a decrease in feed intake, which was noticeable as soon as one-week post-infection in challenged and non-supplemented fish, and kept on decreasing along the whole period compared to the non-challenged control. In contrast, anorexia started later (3 weeks pot-infection) in fish fed feed with the low additive dose and it was not noticed in fish receiving feed with the highest additive dose, which kept a similar feed intake to that of the non-challenged fish. Thus, the typical anorexia induced by the parasite appeared to be mostly overcome with the highest dose of the additive. Similarly, weight, specific growth rate and condition factor were significantly reduced in challenged fish receiving the non-supplemented feed in relation to non-challenged fish, however, in fish receiving the supplemented diets the reduced performance associated to the infection was less dramatic. Indeed, fish receiving feed with the high additive dose did not show significant differences in biometrical parameters and specific growth rate in relation to non-challenged fish. A dose effect of Sanacore®GM was therefore patent and able to mitigate the SGR reduction vs. non-challenged fish. The positive effects of Sanacore®GM, particularly at the high dose inclusion, in refraining most of the disease signs were further confirmed by histopathological data showing the lowest intensity of infection (i.e. mean number of parasites in intestine per infected fish), and by quantitative parasitological data confirming lower prevalence (i.e. % of positive animals with one parasite or more). Since all challenged fish in this experiment were inoculated experimentally with a single dose, detected differences indicate improved ability to constrain parasite development, either by a direct effect on the parasite, or by an immune boosting effect that protects fish from becoming infected and helps to clear off parasite numbers more efficiently.

Two tanks per treatment and 25 fish per tank. Fish fed ad-libitum twice a day. Note that fish receiving the high dose of the additive kept a similar feed intake, weight and SGR to that of the non-challenged. Modified from Palenzuela et al. 2017.

Better understanding of the mode of action of functional feed additives and of their efficacy under field conditions is important to develop effective prevention strategies. The broad spectrum efficacy and immunoregulatory properties of Sanacore®GM have been validated by positive results against the monognean Diplectanum spp (Robles et al. 2017). A trial was conducted with seabass fish (54 g) stocked in tanks located within a pond farm that unfiltered and untreated brackish water. This condition resulted in a natural disease challenge throughout the trial and imitated the fluctuating environmental conditions encountered in the pond farm. Fish were fed a control feed represented by a commercial formula and a treatment feed with same composition and supplemented with Sanacore®GM (0.3%). The trial run from mid-December to min-May, with water temperature ranging from 11°C in January to 23°C in May and water salinity fluctuating between 9 and 17 psu. Diplectanum outbreak was confirmed during February when temperature dropped and resulted in an average mortality during the trial of approximately 11% for control fish and of 4% for Sanacore®GM treated fish (Figure 2). Histopatological analysis and scoring of gill damage (i.e. inflammation, lamellar hyperplasia, lamellar fusion and edema) showed slightly lower values in treated fish than in control fish, with the latter being more affected by other monogenean parasites such as Trichodina and even by Epitheliocystis. In the same line, liver and gut injuries were more marked in control fish and evidenced by clear signs of hepatic and intestinal inflammation. An important outcome of this study was the microbial analysis of intestine showing increased population diversity in treated fish as compared with control fish. We believe that this would explain the success of the Sanacore®GM group fish when coping with Diplectanum outbreak. The increased diversity of the microbial population is in fact considered as a robustness of the population if confronted to any kind of event that can disturb the microbial community. Sanacore®GM can modulate the gut microbiota towards a more stable and robust community, which in turn can promote overall health and provide better resistance to pathogens.

Note that Diplectanum outbreak coincided with the drop in temperature and that feed additive supplementation reduced mortality by 65% in relation to the non-supplemented control group. Modified from Robles et al. 2017.

Nutriad’s aqua team works together with researchers around the globe and serves producers in Turkey to develop disease prevention strategies based on different approaches including the use of functional feed additives. The use of these health promoting additives can partially revert the negative effects of endo- and ecto-parasite infestations, however, these effects are dependent on disease pressure and additive dosage and therefore successful application requires prior evaluation and monitoring of the production conditions. Recent data evaluating Sanacore®GM supplementation on myxosporeans and monogeneans indicates that the mode of action is through a direct inhibition on the parasite as well as through promotion of a protective immune response via modulation of the gut microbiota among other mechanisms. More information available upon request.

We also suggest you to read our previous article titled "Aquatic feed processing with twin screw extrusion".

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