Page 34 - New additives and ingredients in the formulation of aquafeeds

The trial was performed during two consecutive phases in 7 m3 cages: phase 1
(from 28 g to approx. 170 g) and phase 2 (from 170 g to 750 g, i.e. commercial
size). In Phase 1, 880 juveniles of Nile tilapia (GIFT strain, initial weight
28 g) were stocked per cage. 10 replicate cages were fed the control feed,
consisting of a commercial feed (36% crude protein). The treatment feed
consisted of the control feed supplemented with a digestibility enhancing
feed additive (Aquagest® OMF, Nutriad; 3 kg per MT of feed). The treatment
group consisted of 15 replicate cages.
In Phase 2, the stocking density was 800 fish per cage and 4 different
treatments were run with 5 replicate cages per treatment: (1) Control:
fed a commercial feed with 32% crude protein; (2) AG3: control feed
supplemented with the feed additive at 3 kg/MT throughout the entire
cycle; (3): AG 3/1.5: control feed supplemented with the feed additive at 3
kg/MT until 350g and subsequently at 1.5 kg/MT until the end of the trial;
(4) LC-AG2: low cost feed, formulated with protein of lower digestibility and
poorer amino acid profile, supplemented with 2 kg/MT of the feed additive
(7% reduced formula cost compared to the control feed). During Phase 2,
the control group was stocked with fish originating from the control group
during phase 1; whereas the other treatments were recruited from fish
receiving the additive during phase 1. Feeds were produced in a commercial
extrusion line and the additive was included directly in the mixer with all
other ingredients prior to extrusion. Feed distribution was based on feeding
tables four (Phase 1) and three times per day (Phase 2). At the end of Phase
1, all fish, were weighed, average daily weight gain and feed conversion were
determined. At the end of Phase 2, all fish from each experimental cage
were weighed and counted. At harvest, 5% of the population per cage were
processed for fileting. The evaluated parameters included survival, daily
weight gain, feed conversion, fileting yield, viscera weight, liver weight and
visceral fat weight.
At the end of Phase 1, fish supplemented with the feed additive showed
significant improvements on performance compared to the control group,
i.e. 12% better daily weight gain, 5% better survival and 6% better feed
conversion (Figure 4).
Photo 2: Tilapia was
grown from 28 g to
commercial size in
7m3 cages (pictures
provided by Giovani
Sampaio Gonçalves)
32 Innovative approaches to reduce feed cost in aquaculture: optimizing nutrient utilization and gut health