Effects of dietary phosphorus and phospholipid level on growth, and phosphorus deficiency signs in juvenile Japanese flounder, Paralichthys olivaceus

Abstract

A growth experiment was carried out to investigate the effect of dietary phosphorus (P) and phospholipid (PL) concentration, as well as their potential interaction, on growth, feed intake, survival and lipid class composition of whole body and liver in juvenile Japanese flounder. Calcium monophosphate and purified PL (Soybean lecithin acetone insoluble, 88.6% purification) were the P and PL sources, respectively. Nine semi-purified diets were supplemented with 3 levels of inorganic-P (IP) and purified PL, and growth performances were monitored in a 40 day growth trial by using 1 g fish. Results indicated that final weight, weight gain and feed intake significantly increased with increasing P and PL level in the diet. No significant interaction between the two factors on growth, feed intake and survival was observed. Fish fed the diet containing 1.65% P and 5.2% PL gave maximum growth. Ash and P content of whole body decreased in the fish fed the lower P diets. Malformations were observed in opercula of fish fed the non-IP supplemented diets with or without PL supply. Based on scanning electron microscopy observations, the fish fed P-deficient diet showed relatively more perforated spongy area compared to those fed P-sufficient diet. The present study demonstrated that there was no interaction between dietary P and PL on the parameters measured, and dietary PL supplementation is beneficial for growth of juvenile Japanese flounder (1 to 18 g). Phosphorus deficiency signs were characterized by poor growth, deformed operculum, decreased bone mineralization and increment in whole body lipid content in juvenile Japanese flounder.