| Resumo: |
Four types of poly unsaturated fatty acids (PUFA) are essential for all shrimp species, linoleic (LOA, 18:2n-6), alfa-linolenic (ALA, 18:3n-3), eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic (DHA, 22:6n-3) acids. Moreover, the arachidonic acid (ARA, 20:4n-6), even when present, seems to be, in crustaceans, not so important or yet dispensable. It is relevant knowing that cholesterol as much as PUFA are not well absorbed when not followed by a substantial amount of lecithin, reaching 5% of the ration. The sum of PUFA reaches around 3% of the diet, even varying according to the species, stage and ration type. For Penaeus monodon a complex mathematic model was formulated in order to describe the relationships between the requirements of the cited PUFA. Industries involved with feed production on this segment must possess its own adaptation for another species. On the other hand, biochemical knowledge on PUFA n-3 series compounds functions are yet very delayed in comparison to the advances on pharmaceutical industry that investigates the n-6 series, with its prevalence in humans. In this review, the term PUFA is generically used to include ALA, LOA, DPA, EPA, ARA and DHA.
Lipid quality on shrimp nutrition is very important, especially regarding to its content of essential substances. Nutrient intake is instinctively adjusted when animal selects its feeds in the wild. In captivity, it is possible to observe the cholesterol requirement, as in shrimps, as in other crustaceans, since they do not possess the ability to synthesize this indispensable nutrient for animal survival and development. Cholesterol is a relatively small part of the essential lipids for shrimp, and cannot be replaced by phytosteroids. Since cholesterol is the precursor of the ecdisone hormone (which controls molts), it is particularly more necessary during larvae stages. Also, fat-soluble vitamins are vital for shrimp growth. However, vitamins D and K functions are still partially known, because the premises of their functions in vertebrates have no equivalent in crustaceans. In this sense, only the relevance of vitamin E to protect PUFA has an explanation so far. On the other hand, the carotenoid astaxanthin appears to be as effective as an antioxidant that is difficult to justify the need for tocopherol. Dietetic imbalance in essential lipids turns shrimps susceptible to opportunistic infections. This review describes the cholesterol and fat-soluble vitamins importance in shrimp feeding.
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