Page 38 - New additives and ingredients in the formulation of aquafeeds

Figure 6) (Coutteau et al., 2010). This clearly demonstrates the nutrients
present in feeds containing low levels of fish meal and high levels of vege-
table proteins are currently underutilized and require functional additives to
maximize their utilization by the fish’s digestive and metabolic processes.
Photo 3: White shrimp
(Litopenaeus vanna-
mei; with courtesy of
Peter Coutteau)
36 Innovative approaches to reduce feed cost in aquaculture: optimizing nutrient utilization and gut health
Natural
emulsifiers to
enhance lipid
digestion in
shrimp
Shrimps do not tolerate high levels of dietary fat very well. A number
of studies show reduced growth at levels above 10% of dietary lipid.
Nevertheless, shrimp have no or very limited capacity to biosynthesize a
number of lipid molecules which are essential for normal growth, including
cholesterol, highly unsaturated fatty acids and phospholipids. Cholesterol
is a key constituent of cell membranes and precursor for steroid and
moulting hormones. It has been found to be most effective in different
species of shrimp at dietary levels ranging from 0.20% to 0.5%. Cholesterol
levels below 0.10% limit growth in Litopenaeus vannamei , even if the
other nutrients are formulated to satisfy normal requirements (Duerr and
Walsh, 1996). Fishmeal is the major cholesterol source in practical feed
formulations for shrimp with some contributions also coming from fish oil,
squid and shrimp meal. Shrimp cannot bioconvert highly unsaturated fatty
acids (HUFA: 20:5n-3 or EPA; 22:6n-3 or DHA) which need to be provided
at 0.8-1% in the diet via the marine ingredients, mainly fish oil and fish
meal. Phospholipids are a component of cell membranes, building blocks
for lipoproteins (essential for lipid mobilization in the haemolymph), and
constitute a highly available source of choline and inositol (Coutteau et
al., 1997). Although the optimal level may depend on the formulation and
culture conditions, phospholipid requirements are estimated around 1-2%
(equivalent to 1.5-3% liquid lecithin). The combination of suboptimal dietary
levels of cholesterol and phospholipids may be particularly detrimental
to shrimp nutrition due to the interaction between phospholipids and
cholesterol requirements (Gong et al., 2000).
Emulsifying agents are a diverse class of compounds which are able to
disperse fat in water under the form of small droplets (as in milk). In land
animals, emulsifiers are added to the feed to complement the lipid digestive
processes by reducing the size of the fat globules released from the diet
and increasing the efficiency of the lipase activity. Lipid digestion in shrimp
occurs for a big proportion intracellular in the hepatopancreas epithelium