NUTRITION
Do high energetic needs mean high dietary lipid levels? The road to tailored diets for marine fish larvae Wilson Pinto1, Maria Morais1, Sara Castanho2, Ana Candeias-Mendes2, Ana Gamboa2, Florbela Soares2, Susana Pereira3,4, Benjamin Costas3,4, Pedro Pousão Ferreira2 and Luís E.C. Conceição1 Sparos Lda, 2 IPMA – EPPO, Portuguese Institute for the Ocean and Atmosphere (IPMA), 3 Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR), 4 Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto 1
Optimal dietary lipid levels are still unknown for most marine fish larvae Although the quality of commercial microdiets has significantly increased during the last few decades, it is fair to say that our knowledge of the quantitative and qualitative nutritional requirements of fish larvae still remains at the tip of the iceberg. Still, it is generally accepted that fish larvae have high nutritional requirements, mostly due to their fast growth, which in some species/stages can reach over 50% per day, but also due to their energetic predatory and swimming behavioral pattern. Fish larvae have therefore a high requirement not only for proteins, which deposited in muscle tissues are the building blocks for growth, but also for lipids, which are mainly directed towards energy production and are a source of essential longchain polyunsaturated fatty acids (e.g. docosahexaenoic acid - DHA), vital pieces for physiological balance, organogenesis and formation of cellular membranes. In commercial microdiets for fish larvae, proteins account for the largest fraction, generally around 56-62% of diet weight. However, levels found in the lipid fraction are more variable, ranging between 9-20% of diet weight. This variability in dietary lipid levels of commercial microdiets may occur because determining an optimal dietary lipid level for a given species at the early developmental stages is extremely difficult. On one hand, the main metabolic fate of dietary lipids in
Figure 1. Proximal composition of microdiets tested in experimental trials with traditional species. Values expressed in diet wet weight basis; COMM: commercial diet; MFAT and HFAT: diets containing moderate and high fat levels, respectively; HFATDHA: diet containing high fat levels and supplemented with DHA; crude protein percentages are represented in white over the dark blue areas of the circles; crude lipid percentages are represented in white over the medium-light blue areas of the circles; E – crude energy values.
marine fish larvae is towards energy generation. On the other hand, energy production is also dependent on the catabolism of amino acids, which belong to the protein fraction of the diet. Energy production in fish larvae is therefore largely affected by the protein and lipid fractions of the diet, and both factors cannot be dissociated in energy yielding. The term “lipids” is a generic noun for organic compounds that are grouped together on the basis of being soluble in organic solvents, including fatty acids,
Hatchery Feed & Management Vol 10 Issue 2 2022
