A 70-day feeding trial was conducted to assess the nutritional value of Porphyra purpurea meal in experimental diets for juvenile thick-lipped grey mullet. Three isonitrogenous (47% crude protein), lipid and carbohydrate balanced, isocaloric (20 kJ g-l> diets were formulated. The control diet contained fish meal as the principal protein source; in the other two diets, seaweed meal was included to effectively replace 9 and 18% of the fish meal component. The trial revealed that optimal growth, both in terms of weight gain and specific growth rate, was attained in mullet fed the diet without seaweed; increasing levels of seaweed in the diet resulted in reduced growth response. A steady growth rate was observed in all treatments, obtaining satisfactory weight gains with the diets containing seaweed. Feed conversion efficiency, protein efficiency ratio and net protein utilization were also found to decrease with increasing levels of seaweed in the diet.
This preliminary study has demonstrated that the use of the macroalga P. purpurea, as an ingredient in the diets of warmwater fish, such as mullet, has limitations with respect to growth performance and feed utilization. Nevertheless, partial substitution of nutritionally superior fish meal with seaweed may prove to be cost effective. Various approaches towards the possible improvement of the nutritional value of seaweeds are discussed in this context. 0 1997 Elsevier Science B.V.