Protein content determines the nutritional value of the seaweed Ulva lactuca L for the abalone Haliotis tuberculata L. and H. Discus hannai Ino

The nutritional value to abalone of Ulva lactuca L with different tissue nitrogen levels was studied. The seaweed was cultured at two levels of ammonia-N enrichment. Cultures receiving 0.5 g ammonia-N m-2 d-1 ("Iow-N") yielded 164 g m-2 d-1 of fresh thalli containing 12% cmde protein in dry matter and 12 kJ g-l energy; cultures receiving 10 g ammonia-N m-2 d-1 ("high-N") produced 105 g of fresh thalli m~7 d-1 containing 44% protein and 16 kJ g-l energy. High-N and low-N algae and a "standard" mixed diet 005% U. lactuca and 25% Graci/aria conferta (w/w) containing 33% protein and 15 kJ g-l energy were fed to juvenile (0.7-2.1 g) an4 adult (6.9-19.6 g) Haliotis tuberclllata and H. discus hannai in a 16-week feeding trial. Voluntary feed intake of the high-N and slllndard diets were significantly lower than the low-N diet in all the cases. Clear differences in performance between treatments were found in the juvenile and adult abalone of both species. Juveniles fed high-N and standard diets grew significantly faster (specific growtb ratc'of H. tuberculata was 1.03% day-l on high-N algae as compared to 0.72% on low-N algae; H. discus hannai grew 0.63 and 0,3% d\\\\y-l on high-and low-N algae, respectively) and showed much better food conversion ratios. The nutritional value of Ulva lactuca to abalone is greatly improved by a high protein content, attainable by culturing the seaweed with high supply rates of ammonia.