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Environmental Advantages for Alternative Proteins in Trout Diets Two experiments were conducted to evaluate low-phosphorus diets
for rainbow trout using diets formulated with alternative protein sources
from animal and plant sources that have better phosphorus availability.
A 57% fish meal control diet was compared to a diet formulated with
20% fish meal, 20% soybean meal and 20% corn gluten meal, or to a diet
with 20% fish meal, 20% soybean meal, 22% corn gluten meal, 4% poultry
feather meal and 4% blood meal. The crude protein and total phosphorus
content of the diets were 48.1%, 1.7%, 46.5%, 0.9% and 47,4%, 0.8% for
the three diets, respectively. Results indicated no significant differences
in fish growth rate or feed utilization between the three treatments.
In the first experiment the phosphorus retention was higher (56% and
69%) in the two test diets compared to the fish meal control diet (36%).
Nitrogen retention was similar for all three treatments. In the second
experiment with larger fish, phosphorus retention was 36.0 and 22.2%
for the complex and control diets, respectively. The researchers concluded
these experiments indicated that diets containing alternative low-phosphorus
protein meals could both reduce the dependency on fish meals as the
primary protein source in trout diets, and help in lowering the total
phosphorus loaded into the water without a significant loss in fish
performance. The researchers were optimistic that through ingredient
selection and lowering the phosphorus levels in the diet, lower levels
of phosphorus would be excreted into the aquatic environment. |
