Effects of dietary rapeseed glucosinolates, sinapic acid and phytic acid on feed intake, growth performance and fish health in turbot (Psetta maxima L.)

Various antinutritional factors (ANF) present in rapeseed protein products can adversely affect the voluntary feed intake, growth performance and physiology as well as health of fish. The aim of the presented study was to evaluate which ANF is primarily responsible for the mentioned effects. Six identical semi-purified diets based on casein were produced. One unsupplemented basal diet (BD) served as control. The remaining five diets were supplemented with graded levels of glucosinolates (low = GL, high = GH), sinapic acid (low = SL, high = SH) and one level of phytic acid (PA). Diets were fed to triplicate groups of juvenile turbot (Psetta maxima L.) until apparent satiation for 50 days. Voluntary feed intake, growth performance as well as physiology of fish were investigated. Feed intake and growth performance of fish did not differ significantly (p < 0.05) between experimental groups. However, the feed conversion ratio (FCR) increased significantly due to dietary phytic acid supplementation (10 g kg(-1)feed). Also the protein efficiency ratio (PER) showed a strong tendency to decrease in fish fed diet PA (p = 0.0518). Furthermore no significant differences were detected among dietary treatments regarding the proximate final body composition, hepatosomatic index, splenic index and haematocrit of fish. Concentrations of the thyroidal hormones thyroxine (T4) and triiodothyronine (T3) in blood plasma were unaffected in all fish fed experimental diets. It was concluded that higher dietary levels of phytic acid, similar to commercial plant-based diets, can adversely affect nutrient utilisation in fish nutrition. Other investigated ANF did not harm fish performance significantly in applied concentrations when supplemented in a pure grade.