Effect of lecithin on the haematological and condition indices of the rainbow trout Oncorhynchus mykiss (Walbaum)

Rainbow trout Oncorhynchus mykiss (Walbaum) were studied for 98 days for their response to the administration of a 1% rapeseed lecithin supplement in dry pellets. Lecithin tended to stimulate erythropoiesis, which manifested itself as a higher erythrocyte count, a higher haematocrit level and higher haemoglobin concentration during the course of the trial, compared with the control group. The significant differences that were found in the haematological profile, in the parameters of nitrogen metabolism (total protein, blood nitrogen urea, uric acid, creatinine) and mineral metabolism (inorganic phosphate, total calcium) and in the activity of catalytic enzymes (alanine aminotransferase), in certain periods of the trial do not suggest any adverse effects on the state of health of the fish; the levels of haematological parameters remained within the range of reference values. The catalytic activity of the aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase and α‐hydroxybutyryl dehydrogenase as well as the hepatosomatic index and condition factors calculated after Fulton and after Clark were unchanged. Lecithin supplement to the diet caused no clinical changes in the state of health of the fish, nor were any changes ascribable to the administration of lecithin observed on the basis of the patho‐anatomic and histological examination. Considering this and the good results in terms of the supporting antioxidant properties and the effect on growth capacity, recorded in previous experiments, rapeseed lecithin at the tested concentration level can be recommended as a supplement to dry pellets for rainbow trout.