Exogenous protease promotes growth of large yellow croaker (Larmichthys crocea) fed diets with fishmeal substituted by compound plant-ingredients

A net-pen experiment was conducted to assess influences of exogenous protease (EP) and dried porcine soluble (DPS) on dietary fishmeal substitution by a compound consisting of cottonseed meal (CM) and soy protein concentrate (SPC) for large yellow croaker (Larimichthys crocea). A basal diet (BD) was formulated to contain 350 g/kg fishmeal, and a low-fishmeal diet (P0D0) was formulated by substituting 50% of the fishmeal in BD with the compound of SPC and CM. The other three low-fishmeal diets were formulated by adding EP (0.175 g/kg) and DPS (5 g/kg) in diet P0D0 either alone (P1D0 and P0D1) or in combination (P1D1). Fish weighing 19.7 g were given the test diets for 10 weeks. The EP addition significantly influenced final body weight (FBW), weight gain, feed conversion ratio (FCR), retention efficiencies of nitrogen (NRE) and energy (ERE), and ratio of fish-in to fish-out (FIFO), while nitrogen waste was significantly influenced by the DPS addition. The weight gain, FBW, NRE, and ERE were higher, while the FCR, FIFO, nitrogen waste, and phosphorus waste were lower, in fish fed the low-fishmeal diets with EP addition than in fish fed the low-fishmeal diets without EP addition. Fish fed the low-fishmeal diets with DPS addition had lower nitrogen waste compared to fish fed the low-fishmeal diets without DPS addition. The weight gain of fish fed BD did not significantly differ from that of fish fed P1D0, P0D1, and P1D1, but was higher than that of fish fed P0D0. The production performance of fish fed BD was similar to that of fish fed P1D0, but was separated from that of fish fed P0D0. The villus height of intestine was lower in fish fed P0D0 than in fish fed BD, P1D0, P0D1, and P1D1. The intestinal trypsin activity was higher, while the nitrogen waste was lower, in fish fed BD than in fish fed P1D0, P0D1, and P1D1. This study indicates, for the first time, that the EP addition at 0.175 g/kg can promote growth of large yellow croaker fed the diets with fishmeal substituted by the compound of CM and SPC.