Replacement of fishmeal by soya protein concentrate in the diets of Totoaba macdonaldi (Gilbert, 1890) juveniles: effect on the growth performance, invitro digestibility, digestive enzymes and the haematological and biochemistry parameters

The potential of soya protein concentrate (SPC) as an alternative protein source in diets for Totoaba macdonaldi juveniles was evaluated. Seven isonitrogenous and isolipidic diets were formulated containing 15-100% SPC (SPC15, SPC30, SPC45, SPC60, SPC75, SPC90 and SPC100) to replace fishmeal (FM-protein), and a FM-protein-based diet without SPC was used as a reference diet (RD). Each diet was randomly assigned to triplicate groups of 20 totoaba (50 +/- 1.0g) and was fed twice daily to apparent satiation. After 60days of experiment, effects on totoaba were evaluated. Growth performance in fish fed RD to SPC45 was similar. The maximum FM-protein replacement for weight gain (gkgABW(-1)day(-1)) was estimated to be 34.17% using a broken-line model. In vitro digestibility of fish fed RD, SPC15 and SPC30 was similar. Trypsin activity was higher in fish fed the RD (9.38 +/- 0.52 mUx10(-3) mg protein(-1). Chymotrypsin activity was similar in fish fed RD, SPC15 and SPC30. Activity of alkaline protease and phosphatase was similar in fish fed RD, SPC15 and SPC30. Red blood cells (RBC) were the highest in fish fed RD to SPC60. Fish fed the RD, SPC15 and SPC30 present the highest haematocrit (HT) and haemoglobin (HB) content. Diets SPC90 and SPC100 presented similar MCV and MCHC. Total protein (TP) profile overall decreased in fish fed SPC90 and SPC100, pointing to nutritional hypoproteinemia due to deficient digestion and absorption. These results indicate that SPC-based diets could be used efficiently by totoaba with FM-protein replacement of less than 45%.