Functional Feeds as Feed Additives
A feed additive can be defined as: a pure substance or a mixture of substances that is intentionally added to feeds and exert a single or several different specific functions; includes all nutritive or not, inert or active, natural or synthetic chemical compounds. Main feed additives used in the shrimp nutrition have traditionally included: antibiotics, probiotics, nutrients, pigments, enzymes, preservatives, antioxidants, attractants and appetite stimulants.
Particularly of relevant importance, some feed additives have been characterized that stimulate the speed of growth or the ability to reach the maximum sizes of the species. In general, the main reason triggering the search for feed additives has been the necessity of the aquaculture productions to promote the conditions for an optimal development, (meaning to get better growth in the smaller time). Thus, the weight and length gain (as growth parameters) and the survival (as health parameter) arise as the few indicators suitable for the monitoring of the culture organisms development.
It is actually hard to conceive the functional feeds as the only source of nutrition for marine organisms, basically because the investigations have not been conducted with such objectives so far. Furthermore, it would be pretentious to satisfy all the nutritional requirements while looking for relevant physiological responses when complete natural feeds are used. However, it seems much logical to attempt the enrichment of conventionally used feeds with particular functional elements bearing certain physiological effect in marine organisms.
As previously discussed, the use of feed additive in the marine organisms diet is intended to promote certain physiological effects, leading to: i) growth stimulation or ii) health promotion (which is indirectly related to growth stimulation).
Interestingly, the expected effects of feed additives in the shrimp nutrition are similar to those expected for the functional feeds, since they both have positive effects on the animals health and development beyond their ability to cover basic nutritional requirements. Nevertheless, the functional feeds distinguish from feeds additives in: i) they are complete feeds (not isolated compounds), ii) their ability to promote specific physiological effects, iii) their attractability (in terms of palatability and/or scent), which is particularly desirable in practical nutrition of marine cultures.
Yet, it is difficult to find precise examples of functional feeds used as feeds additives in aquaculture nutrition. In addition, some of the few related examples can lead to a doubtful application of the functional feeds concept. The use of probiotics in aquaculture nutrition, provide us with an example of functional feeds for the culture marine organisms.
Probiotics, which are micro-organisms (or their products) with health benefit to the host, have found use in aquaculture as a means of disease control, supplementing or even in some cases replacing the use of antimicrobial compounds.
A wide range of micro algae, yeasts and Gram-positive and Gram-negative bacteria has been evaluated. However, the possible mode of action of the probiotics include the inhibition of the colonization of potential pathogens in the digestive tract by antibiosis or by competition for nutrients and/or space, alteration of microbial metabolism, and/or by the stimulation of host immunity.
Several results shown the probiotics may stimulate appetite and improve nutrition by the production of vitamins, detoxification of compounds in the diet, and by the breakdown of indigestible components.
Another example of functional feed in aquaculture nutrition is the experimental use of the palm oil. Palm oil-containing formulations increase the alimentary conversion and enhance the growth, the protein efficiency and the reproductive capacity of certain Malaysian prawn species.
Also palm oil in the diets of catfish and Atlantic salmon resulted in growth and feed efficiency comparable to that of fish fed equivalent levels of dietary fish oil; however the inclusion of 8% of palm oil in African catfish diets significantly improved growth performance, dietary protein retention, and vitamin E concentration in body muscle.
These interesting results could be related with the high oxidative stability of the palm oil which reduces the incidence of rancidity when oils are incorporated in feeds. Additionally, the antioxidant properties due to this high content of vitamin E and carotenoides could play an important role against the normal and abnormal oxidative process in cultured organisms, favoring the use of feed nutrients to growth and reproduction and not to defense, and/or repair processes related to diseases.
Similarly, the seaweed by-product known as kelp meal (obtained from Macrocystis pyrifera) have been found to exert a variety of effects that can support its acceptance as a functional feeds for shrimp nutrition. Several authors have reported that the addition of kelp meal at various percentages in the shrimp diet not only increases the growth and the capacity of the organisms to resist the attack of pathogenic microorganisms, but also improves the stability, attractability and palatability of feeds. Underlying such physiological effects, sodium alginate and fucoidan (sulphate polysaccharide) have been identified.
Therefore, the search for functional feeds in the aquaculture nutrition will surely include vegetal and animal origin feeds, containing active compounds able to modulate relevant functions in the consumer organisms.
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Image source: Aquanetviet