1. Introduction
Fish, as most animals, show “nutritional wisdom” and select from among different food sources to compose a balanced diet that meets their nutritional requirements [1], [2] and [3]. Dietary selection was first studied in insects and subsequently used on farmed animals, which can be unable to reach their intake target when fed on single nutritionally unbalanced foods. Moreover, animals show their capacity to self-select a balanced diet when fed more than one (complementary) nutrient source. According to Raubenheimer and Simpson [4] and [5], animals suffer excesses and/or deficiencies of individual nutrients while attempting to achieve a point of nutrient intake through “rules of compromise” that reflect the costs and benefits of over/under ingesting specific nutrients. In fish, self-selection experiments have showed that they are able to self-compose a balanced macronutrient diet [6] and [7], and detect small differences in the level of micro-nutrients such as zinc [8] or vitamin C [9], or the addition of exogenous phytase to plant-based diets [10]. However, most studies on amino acid imbalance and dietary selection in fish have been conducted using mammalian models [11].