A two month feeding trial was conducted in silvery-black porgy (Sparidentex hasta) juveniles (initial mean body weight, 16.7 g) to determine the amount of soy products (SP) that could replace fishmeal (FM) in formulated diets without reducing growth performance. Six isoproteic (ca. 50%) and isoenergetic (ca. 22.4 MJ kg−1) diets were formulated in which 15% (SP15), 30% (SP30), 45% (SP45), 60% (SP60) and 75% (SP75) of FM was replaced by SP, whereas the control diet (FM) was prepared with FM as the major source of protein. Feed intake, growth performance, feed utilization and digestibility of dry matter, protein and lipid significantly decreased by increasing dietary SP supplementation (P b 0.05). Fish fed with the SP75 diet showed signs of hyperlipidemia such the highest hepatosomatic index (HSI), high whole body lipid content aswell as high plasmacholesterol, triglyceride and very low density lipoprotein levels (P b 0.05). Whole body lysine, histidine, methionine and phenylalanine concentrations were lowest in fish fed with the SP75 diet (P b 0.05). Concentrations of glycine and taurine decreased in the whole body with increasing dietary SP level. The activity of the trypsin, lipase and α-amylase significantly decreased in pyloric caeca, anterior, mid and posterior intestine of fish with increasing dietary SP inclusion (P b 0.05). Fish fed with the SP75 diet showed signs of anemia such as decrease in red blood cell counts and hematocrit, but increase in the mean cell volume. Plasma inorganic phosphorous and alkaline phosphatase decreased and increased, respectively with increasing dietary SP level (P b 0.05). The broken-line regression method using feed conversion ratio (FCR) and weight gain (WG) data allowed us to estimate that the maximum replacement of FM with SP in silvery-black porgy diets was between 16.5 and 27.3%. Statements of relevance: Silvery-black porgy (Sparidentex hasta, Valenciennes 1830) is a commercially valuable carnivorous fish species in Oman Sea and Persian Gulf region for supporting marine aquaculture activities. Thus, the aim of present study was to provide insight into the potential ability of silvery-black porgy in using plant proteins sources, by evaluating the effects of dietary replacement of fish meal by soy products (soybean meal and isolated soy protein) in this fish.

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