rainbow troutAn Agricultural Research Service study found that rainbow trout fed diets containing nut meal have similar survival and growth rates as trout fed fish meal.Photo credit: Stephen AusmusThanks to researchers at the U.S. Department of Agriculture (USDA), a new feed ingredient made from tree nuts is available to fish farmers.

In an effort to develop ingredients high enough in protein for use as aquacultural 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.

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 color, size and other qualities.

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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 percent fish meal and 49 to 58 percent nut meal had survival and growth rates similar to those of trout fed a diet containing 55 percent 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.

Read more about this research in the October 2016 issue of AgResearch online.