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Meeting growth potential of fish larvae: microdiet formulations and technology By Luis Conceição*, Wilson Pinto, SPAROS Lda, Olhão, Portugal
Microdiets for early weaning of marine fish larvae: there is room for improvement Replacement of live feeds early in development has been a priority in academic and industrial marine fish larval research since the 1990s. Progress has been considerable, with good weaning results being currently delivered by several commercial microdiets, in particular for major cultivated species such as European seabass and gilthead seabream in Europe and red seabream and olive flounder in Asia. Recently, significant progress on weaning has also been achieved for some candidate species for the expansion of the aquaculture industry in Southern Europe, such as Senegalese sole (Canada et al., 2016; Engrola et al., 2016; Pinto et al., 2015, 2016) and greater amberjack (Conceição et al., 2016a). Still, there is plenty of room for improvement in microdiets for marine fish larvae, in particular for the very early stages.
Even if we have a reasonable understanding of what fish larvae roughly require in their diets: high levels of protein, essential fatty acids, and micronutrients, provided by highly digestible ingredients, the exact nutritional requirements are poorly understood (Hamre et al. 2013). Nutrition is important in terms of survival and growth performance, but also for a healthy immune system or a normal skeleton formation. This is true for the more traditional cultured species such as European seabass, gilthead seabream, red seabream and olive flounder, and certainly also for the emerging species.
Microencapsulation and binding technologies are to improve microdiets Conceiving an ideal microdiet for fish larvae is only possible through a holistic approach. Although its nutritional adequacy to the requirements of a given species is the first factor to be consid-
ered, the technological process involved in microdiet production must also be taken into account. Technology largely influences the physical properties of the microdiet in water, affecting ingestion, nutrient loss to the surrounding water (leaching) and digestion (Khater et al., 2014). Optimal physical properties such as floatability, sinking speed, dispersion both in tank surface and water column will ensure a higher ingestion by fish larvae, ultimately determining the success of weaning and to what extent growth potential is realized. In addition, the high surface-to-volume ratio of microdiet particles makes them prone to leaching of water soluble nutrients, particularly in smaller sizes (< 0.5 mm). This loss may compromise larval growth by reducing the nutrient input to larval bodies, as well as lead to degradation of the rearing water quality. Most commercial microdiets for fish larvae are produced by extrusion, a costeffective technological process where a