Impact of fishmeal replacement with poultry meal on rainbow trout (Oncorhynchus mykiss) nutrition, physiology and performance

The future sustainability of aquaculture will depend in part on the reduction of fishmeal (FM) used in fish feeds and the development of economically alternative protein sources. Poultry meal (PM) is one example of an alternative protein source. The aim of this study was to understand the effects of FM replacement with PM on nutrition, physiology and performance of rainbow trout. Four independent experiments using isoenergetic and isonitrogenous feeds (22 MJ GE `kg^-1` DM, 400 g `kg^-1` DM of crude protein) were carried out. An initial study investigated the effect of replacing FM protein with increasing amounts of PM protein in which 0, 20, 30 and 40% FM protein was replaced with PM protein. Fish were grown in freshwater at 15°C for 84 days, during which time they were fed twice daily at 2% bw `d^-1`.The results indicated that PM protein can be used to replace up to 40% of the FM protein without impaired fish growth, apparent digestibility of crude protein, insulin like growth factor I (IGF I) and cortisol. A further study was carried out to determine the effects of replacement on apparent digestibility where twelve isoenergetic and isonitrogenous feeds were formulated in which 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95 and 100% FM protein was replaced with PM protein. Fish were grown in freshwater at 15°C for 27 days, during which time they were fed twice daily until satiation. Faeces were stripped from fish on day 3, 9 and day 27. Effects of poultry meal inclusion level on apparent digestibility showed the significant negative linear relationships between PM inclusion and apparent digestibility measured as AD crude protein, AD total lipid and AD gross energy. There were no significant differences in AD crude protein or AD total lipid between the three adaptation times. However, AD gross energy increased over time. A further experiment evaluated the effects of temperature on FM with increasing PM at two different temperatures (15°C and 20°C). Twelve isoenergetic and isonitrogenous feeds were formulated in which 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95 and 100% FM protein was replaced with PM protein. Fish were fed twice daily at 2% bw `d^-1` for a period of 112 days. Results indicate the high potential of PM as an alternative protein source at optimal and high temperatures. In addition, result on histology of the distal intestine showed that increase in the number of goblet cells (GC) and decrease in the width of supranuclear vacuoles (SNV) in fish fed diets containing greater than 90% of PM protein at both temperatures. The last experiment was designed to test the effects of supplementary essential amino acids (L-lysine and L-histidine) on rainbow trout. Fish was fed either a set daily ration of 1.7% bw·`d^-1` or fed to satiation. The results indicated that supplementary essential amino acids (EAA), L-lysine and Lhistidine in PM diet did not improve growth of rainbow trout.