Evaluation of the nutritional quality of co-products from the nut industry, algae and an invertebrate meal for rainbow trout, Oncorhynchus mykiss

• Diets with mostly almond, pistachio, algae, and mussel meal were fed to young trout.
• Fish fed nut meals had equivalent growth and survival of trout fed a fishmeal diet.
• Digestibility of almond and pistachio meals was similar to fishmeal.
• Non-human use nut meals are palatable, digestible and support rapid growth.

The static supply and increasing demand for fishmeal has created a need to evaluate a variety of alternate proteins. Many species of algae are being grown as a potential source of bio-fuels, and mussel meals have been shown to increase feed intake. The tree nut industry is based primarily on whole nuts with production totaling ~ 1,081,000 tons in California during 2010. A portion of this production does not meet criteria for certification and must be sold for “non-human uses”. Evaluation of ingredients included three types of experiments with rainbow trout: fry screening study, digestibility study, and growth study. First feeding trout were fed a control diet containing 45% fishmeal and the test diets contained 5% fishmeal with the remainder of the protein replaced by the test ingredients. Trout gained between 636 and 1331% of their initial weight after 6 weeks. Trout fed the pistachio and almond meals gained as much weight as trout fed the fishmeal diet, but trout fed the algae's and mussel meal diets grew much slower and were dropped from further evaluation. Apparent digestibility coefficients (ADCs) for crude protein, lipid, and amino acids were determined for pistachio and almond meals, fishmeal, whey protein and soy protein concentrate (SPC) for comparison. Almond and pistachio meals had ADCs for protein, fat and amino acids similar to fishmeal, but phosphorus ADC for pistachio meal was 27% compared to 40% for fishmeal. In the final study, trout with an average initial weight of 20 g were fed one of ten diets for 12 weeks. There were two series of diets; protein from fishmeal was either 50% or 100% replaced with pistachio or almond meal, or the protein from SPC was either 50% or 100% replaced with pistachio or almond meal. The trout fed the nut meals in the fishmeal series all had weight gains equivalent to trout fed the fishmeal control (753%) except the trout fed the partial replacement with almond meal (614%). When SPC was replaced with the nut meals, growth of the fish fed the SPC diet (648%) was the same as fish fed the nut meals except for the fish fed the 100% replacement with pistachio meal which had a greater gain of 830%. These three studies demonstrate that pistachio and almond meals are palatable, digestible, and support high levels of growth whether replacing fishmeal or SPC.