20 Feed Technology
Nursery diet for freshwater fish: A concentrate of technology By Frédéric Baron and Delphine Weissman
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nhanced production of high quality and healthy fry is the key target for a successful and competitive expansion of the aquaculture industry (Valente et al., 2013). During larval and nursery stages, the growth potential of freshwater species like tilapia, African catfish and Pangasius is exponential and needs to be fully supported. The primary nutrients source for farmed fish is in formulated complete feed. Consequently, technology and know-how are mandatory to provide feeds adapted to each species at each stage. Nursery feeds are crucial for this sensitive period. Therefore, they must be precisely designed with the correct nutritional requirements. These feeds need to be designed to comply with physical pellet quality, feed intake and nutritional efficiency. Precise technology with specific formulation is necessary for the starting phase feeds.
Precise nutrition and adapted formula DP/DE ratio
Understanding the raw materials characterisation and nutritional requirements of the fish for development are crucial to formulate feeds using digestible nutrients. Dietary protein digestibility is important to determine how efficiently the ingested proteins can be utilised by fish fry. ADM’s R&D facilities in Vietnam conducted trials and compiled them in a meta-analysis that clearly shows the effects of digestible protein intake on young tilapia growth (Figure 1). The right ratio of digestible protein/digestible energy (DP/DE) in the diet formulation optimises growth and avoids massive nitrogenous discharges that may pollute the aquatic environment (Figure 2).
they do not have the same nutritional dependence on HUFA (omega- 3) compared to marine species (Kolkovski et al., 2009). Nevertheless, during nursery phase, cell multiplication is constantly occurring and phospholipids are crucial to complete the lipidic profile of nursery diet. Phospholipids are structural constituents of biomembranes and are in high demand during the nursery phase due to their importance to fish development.
Minerals, vitamins and functional additives
Ensuring an adequate dietary supply of macro- and microminerals for farmed fish is essential for proper somatic and skeletal growth, health and final flesh quality. In addition to morphological changes and exponential growth, young fish are exposed to numerous stressors such as handling, grading, vaccination, transferring between different culture systems or farms, mixing of populations, density and water quality variations, multiple pathogenic pressure, etc. At the same time, it is a period when both the immune and digestive systems are still immature. Therefore, young fish need high quality feeds with the correct quantity of specific minerals and vitamins. Key functional additives for strategic objectives should be included in the diet to better support fish during this critical stage and beyond.
Digestive enzyme activity
In farming, feed efficiency for maximal growth in animals depends on nutrition profile, ability to consume, digest, absorb and metabolise nutrients from feed (Umalatha et al., 2016). Nutrient utilisation in aquatic animals depends on digestive enzyme activity, which changes during fish growth (Kolkovski, 2001). Since each age group has different digestive enzyme activity, fish also has different nutritional requirements during growth. Therefore, it is necessary to develop feed formulation that is suitable for different sizes of fish.
Lipids
Freshwater fish species possess the ability to desaturate and elongate the C18 essential fatty acids chain to a longer unsaturated fatty acid chain (HUFA). Hence,
Figure 1. Young tilapia daily growth vs digestible protein (DP) intake July/August 2022 AQUA Culture Asia Pacific
Figure 1. Figure Young 1. tilapia Young daily tilapiagrowth daily growth vs vs
Figure 2. Young tilapia daily growth vs digestible protein/digestible energy (DP/DE) ratio. Source: ADM internal R&D data
