12 December 2011 Seaweed nutri-biotechnology: Adding value to aquaculture feed Upasana Mishra1, *Soibam Khogen Singh1, S. Dam Roy1, Pronob Das1, S. C. Mandal1 and N. Ashalaxmi2 Seaweeds are macrophytic algae, a primitive plant lacking true roots, stems and leaves. Most seaweed belongs to one of three divisions - the Chlorophyta (green algae), the Phaeophyta (brown algae) and the Rhodophyta (red algae). There are about 900 species of green seaweed, 4000 red species and 1500 brown species found in nature, out of which 221 species are utilized commercially. Agar-agar, agarose and carrageenan are commercially valuable substances extracted from red seaweeds and are used extensively in many industries. Currently, there are 42 countries with reports of commercial seaweed activity. China is first in seaweed production, with Laminaria sp. accounting for most of its production, followed by North Korea, South Korea, Japan, Philippines, Chile, Norway, Indonesia, USA and India. These top ten countries contribute about 95 percent of the world’s commercial seaweed volume. About 90 percent of seaweed production comes from culture based practices. The most cultivated seaweed is the kelp Laminaria japonica, which alone accounts for over 60 percent of the total cultured seaweed production, while Porphyra, Kappaphycus, Undaria, Eucheuma and Gracilaria make up most of the rest, to a total of 99 percent. Until now, the seaweeds are used mainly for commercial phycocolloids extraction and human consumption. At present, seaweeds with elevated protein content and production rates are receiving increasing attention as novel feeds with potential nutritional benefits and as possible ingredients in fish diets. Apart of their potential nutritional value as protein substitutes, these macroalgae may also give an important contribution to fish diets as lipid sources and binding or coloring agents. Research findings based on biochemical analysis and immunomodulating potential has paved a novel approach towards feed formulation using these resources. Many seaweeds are rich sources of protein and posses several nutraceuticals values. This paper summarizes the major applications of seaweeds as an aquafeed ingredient and the possible value it may add to the present level of feed formulation. Seaweeds as a Rich Protein Source Seaweeds are rarely promoted for the nutritional value of their proteins. The use of seaweeds with high protein levels in the production of foods for farmed fish could be another application of this marine plant resource. Few studies have been undertaken on the quality of seaweed proteins because the presence of phenolic compounds and large amounts polyanionic cell wall mucilages make extraction of protein from seaweed difficult. The protein content of seaweeds differs according to species. Generally, the protein fraction of brown seaweeds is low (3-15 percent of the dry weight) compared with that of the green or red seaweeds (10-47 percent of the dry weight). Except for the species Undaria pinnatifida (wakame), which has a protein level between 11 and 24 percent (dry weight), most industrially exploited brown seaweeds (Laminaria digitata, Ascophyllum nodosum, Fucus vesiculosus and Himanthalia elongata) have a protein content lower than 15 percent (by dry weight). In some green seaweed, such as the species belonging to the genus Ulva, the protein content can represent between 10 and 26 percent (dry weight) of the plant. Higher protein levels were recorded for the red seaweeds such as Porphyra tenera (47 percent of dry mass) or Palmaria palmata (35 percent of dry mass). The beneficial effect of the Porphyra meal used as a food additive in the diet of red sea bream has been evaluated where the seaweed incorporated diet appeared to improve body weight gain and increased the triglyceride and protein deposition in muscle. Seaweeds, such as Gracilaria bursa-pastoris, Ulva rigida and G. cornea, have great potential as alternative ingredients in diets for European sea bass juveniles at dietary inclusion levels up to 10 percent for G. bursa-pastoris and U. rigida and up to 5 percent inclusion level for G. cornea with no adverse effects on growth performance and feed utilization efficiency (Valente et. al. 2006). Feeding trials with rainbow trout showed that incorporation of 10 percent Porphyra dioica and Ascophyllum nodosum increased the carcass protein content without any significant negative effect (Table 1). Amino Acid Content in Seaweeds In most seaweed, aspartic and glutamic acids constitute together a large part of the amino acid fraction. In Fucus sp. these two amino acids can represent between 22 and 44 percent of the total amino acids. In the green seaweeds, the level of these two amino acids can represent up to 26 and 32 percent of the total amino acids of the species Ulva rigida and Ulva rotundata, respectively. However, the glutamic and aspartic acid levels seem to be lower in red seaweed species such as Palmaria palmata and Porphyra tenera, with 14 and 19 percent of the total amino acids, respectively.
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