Freshwater mussel meal as new alternative ingredient for rainbow trout (Oncorhynchus mykiss) feeds: growth performance and histomorphological analyses

Alternative raw materials unsuitable for human consumption might represent a great interest in animal nutrition. Freshwater bivalves represent an unexploited potential feed resource. The effects of freshwater mussel Sinanodonta woodiana meal on growth performance, histomorphology, and morphometric characteristics of the digestive system of rainbow trout ( Oncorhynchus mykiss ) were evaluated. A total of 540 rainbow trout juveniles were fed with three experimental diets consisting of fish meal (FM), fish by-product meal (FPM), and freshwater mussel meal (MM). After 90 days, the fish tripled their initial weight, despite fish fed with MM showed lower weight gain, specific growth rates, and higher feed conversion ratio than those fed with control diets. It has been estimated that the total production period of fish fed with the MM diet was 12–14 days longer than fish fed with FPM and FM, respectively, due to lower growth rates. Histological and morphometrical analyses did not reveal any diet influence on the severity of the observed lesions both in the gut and liver. No negative effects were observed with the inclusion of the MM; therefore, the use of this ingredient could be considered for rainbow trout feeding.