If pistachios or almonds are too big, too small, or too green, they're not used for human food, but they still have some value in fish feed.
Scientists at the Agricultural Research Service (ARS) Small Grains and Potato Germplasm Research Unit in Aberdeen, Idaho, worked with Adaptive Bio-Resources, LLC, to evaluate nuts as an alternative to fish meal. The interest to develop ingredients high enough in protein for use as aquafeed is high.
ARS fish physiologist Rick Barrows examined methods to modify nutritional composition to increase protein in a nut mixture made from pistachios and almonds that did not meet consumer standards for colour, size and other qualities.
Study results on nut meal promising
Barrows and his colleagues evaluated the nut mixture in separate studies. They found that young rainbow trout fed nut meal performed as well as those fed fish meal. Trout fed a diet containing 5% fish meal and 49 to 58% nut meal had survival and growth rates similar to those of trout fed a diet containing 55% fish meal.
Results showed that nut meal is highly digestible, palatable, and supports high growth rates in rainbow trout. Fish fed the nut diet grew very quickly, according to Barrows. Trout fed nut meal in the study all had weight gains equivalent to trout fed fish meal, except when the nut meal contained only almond instead of almond and pistachio.
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