Effect of graded levels of dietary seaweed (Ulva sp.) on growth, hematological and serum biochemical parameters in dusky kob, Argyrosomus japonicus, sciaenidae

This study was designed to assess the effect of incorporating graded levels of green macroalgae seaweed (Ulva sp.) into diets of juvenile dusky kob (Argyrosomus japonicus) on growth performance, hematology and serum biochemistry. Five experimental diets were formulated to contain 0 (Ulva0), 50 (Ulva50), 100 (Ulva100), 150 (Ulva150) and 200 (Ulva200) g seaweed meal/kg commercial kob feed on a dry matter basis. Seventy-seven dusky kob fingerlings (mean body mass 9.14 ± 0.30 g) were distributed into each of 20 experimental tanks and offered diets at 2.8% body mass. Weight and length of fish were measured weekly for 9 weeks. At the end of the feeding trial, fish fed Ulva50 had higher body mass (38.20 ± 1.38 g) compared to those fed the other three Ulva-based diets. Fish offered Ulva200 had significantly (P < .05) lower body mass (13.10 ± 0.53 g) compared to the rest of the groups. The control group achieved specific growth rate (SGR) of 2 g day−1, followed by Ulva50 group at 1.55 g day−1, while the Ulva200 group attained the lowest SGR of 0.54 g day−1. The highest (P < .05) feed conversion efficiency (FCE) (0.14) was recorded for the control group while the Ulva150 group had the lowest FCE (0.08). Lymphocyte, monocyte, eosinophil, basophil, thrombocyte and neutrophil counts were not influenced (P > .05) by dietary treatments. However, the levels of both blood cholesterol and alkaline phosphatase tended to decrease as dietary Ulva inclusion levels increased. These results indicate that Ulva could be incorporated at the rate of 50 g kg−1 in future commercial dusky kob diets without any negative effects on feed utilizationa and growth performance. Hematology and serum biochemistry results indicate that dietary inclusion of Ulva had no adverse effects on physiological status of the fish.