In order for aquaculture to satisfy the increasing demand for farmed fish, it is essential that the sector continues searching for suitable alternatives to fishmeal (FM) that are both cost-effective and widely available. Over the last decades, plant proteins have been used successfully to reduce the inclusion levels of FM in the diets of most farmed fish species, but the high inclusion levels reduce feed intake, fish growth and nutrient bioavailability in fish body, having also negative impacts on the aquatic environment (Bell & Waagbø, 2008;Hardy, 2010). Further, the prices of many plant proteins have increased dramatically over the last decades because of the increasing demand for their use in feeds, human foods and ethanol production (Hardy, 2010). Of most importance, however, is the fact that as the aquafeed sector is expanding to satisfy the increasing demand of intensive aquaculture for aquafeeds, greater amounts of FM are required; thus, the exploration for suitable and cost-effective protein alternatives is ongoing.
AbstractTwo feeding trials examined the replacement of fishmeal (FM) with poultry byproduct meal (PBM) in the diet of juvenile Sparus aurata. In Feeding trial I (100 days), three diets were formulated, where FM protein was replaced by 50% (PBM50) and 100% (PBM100) PBM, while in Feeding trial II (110 days), four diets were formulated using the same FM control diet, but FM was replaced at lower levels: 25% (PBM25), and 25% (PBM25 + ) and 50% (PBM50 + ) with the supplementation of lysine and methionine amino acids. PBM protein can successfully replace 50% of FM protein in the diet of S. aurata without adverse effects on survival, feed intake, growth performance and feed utilization, given that the diet is balanced with lysine and methionine.The proximate composition of body and muscle was unaffected by the diet, but the total FM replacement resulted in reduced lipid and energy contents in fish. A fifty per cent FM replacement by PBM did not affect haematological parameters indicating a good fish health. Similarities in trypsin and chymotrypsin activities with FM-fed fish suggest a high digestibility of PBM. High dietary levels of PBM reduced the liver gene expression of GH/IGF axis and of cathepsin D suppressing fish growth and modulating the protein turnover.
K E Y W O R D Sdigestive enzymes, fishmeal replacement, gene expression, gilthead seabream, haematological parameters, poultry by-product meal
