After hatching eggs, during the consumption of yolk sac, fish larvae are commonly named as yolk larvae. When beginning the exogenous feeding (commonly with artemia), they are only named larvae. In this moment, despite the active swimming behavior to looking for food, system and internal organs still are forming. After that period (at least 15 days after hatching) labeled “larvaculture” with total development of all external and internal structures (excluding reproductive organs), the fish larvae became a juvenile [1,2]. There are two forms of development to fish larvae: precocious larvae – they pass for a long time of endogenous feeding, ensuring an adequate time to develop internal organs. When they reach juvenile stage, its digestive system has a pattern such as an adult (stomach with gastric glandules and enzymatic activity). For altricial larvae-they have a short yolk sac (during only 2 or 3 days) depending on water temperature. Larvae have a rapid development before total consumption of yolk sac, open mouth and anus, functional swim bladder, eyes and rudimentary digestive system. Due to the inability of some fish larvae to reach metabolic maturity of digestive system, there are two hypotheses to explain its digestive process. At the beginning, scientific academy believed that larvae could use some digestive enzymes from the autolyze of exogenous living feed. However, nowadays, this first hypothesis is not so much accepted because some fish larvae has demonstrated alkaline enzymatic activity, ensuring the digestive process without the factor “autolyze” [3-5]. There are some reports which can corroborates with the statement “larvae do not need of exogenous enzymes to digestive process” such as Clupea harengus [6], Sardinops sagax [7] and Dicentrarchus labrax [8]. According to larvae with three days after hatching have zymogen granules in the pancreatic duct and clearly enzymatic activity (trypsin) [8] also reported elevated activity of the enzyme amylase and trypsin in flounder larvae at the time of mouth opening, and the presence of enzymatic capacity before the first exogenous feeding suggests that these activities were not induced by feeding. The use of living feed still represents a high investment for fish farmer, but profitable if applied in intensive systems of production. Nonetheless, it could be reduced (costs) with the early feeding transition passing the living feed to inert diet. According to Portella and [8], this period (feeding transition) is a critical point for most of fish species affecting growth and survival. Therefore, an adequate feeding during the larval development and transition play an important role because the different nutritional needs for each stage. Vitamins and minerals are an important part of the diet to ensure an adequate cellular metabolism and animal development. These nutrients participate of all important metabolic process (protein, carbohydrate and lipids) and functions of coenzymes, enzymes, hormones, DNA, RNA, NADP and CoA forming [9-11].

These nutrients (vitamins and minerals) can aid in weight gain, specific growth rate, apparently feeding conversion and immunological response, if provided at adequate concentration. When observed an unbalanced diet, not what the proportion (more or less nutrient), can occur problems as bad body formation, immunosuppression and poor growth performance [11-14]. Chose the better living feed depends on the fish species as well as its nutritional needs during the larvaculture. The main factor to be considered is the size (size of a living feed must be lower than mouth size of larvae), ranging from the 0.003 to 1cm. For some small fish larvae at the beginning (mainly small ornamental fish), they need to eat some species of microalgae (Nannochloropsis sp or Tisochrysis sp) [15]. Rotifer and ciliated protists are the second stage regarding about size, still representing an initial feeding during the larvaculture. The next, and most used for all fish larvae reared in captivity is artemia saline, representing the better nutritional feed for marine or freshwater fish species [16-22

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