Nitrogen allocation of Gracilaria tikvahiae grown in urbanized estuaries of Long Island Sound and New York City, USA: a preliminary evaluation of ocean farmed Gracilaria for alternative fish feeds

The red seaweed, Gracilaria tikvahiae McLachlan, was cultivated in open water farms in urbanized estuaries of Long Island Sound (26-30 psu of salinity) and New York City (20-25 psu), USA in 2011. Plants were harvested monthly from summer (August, 24C) to fall (November, 13C) and analyzed for total nitrogen, protein, and amino acid content. On a dry matter (DM) basis, nitrogen and protein significantly increased over the harvest period until October and then plateaued. Nitrogen increased from 22 1 g kg -1 DM in August to 39 3 g kg -1 DM in October (p < 0.001). Protein increased from 107 13 g kg -1 DM in August to 196 5 g kg -1 DM in November (p < 0.001). With two exceptions, amino acid concentrations expressed on a crude protein (CP) basis were similar over the harvest period. Essential amino acids accounted for 48 1% of all amino acids present with lysine and methionine averaging 56 2 g kg -1 CP and 18 1 g kg -1 CP, respectively. Histidine was underrepresented among essential amino acids and averaged 13 1 g kg -1 CP. Taurine ranged from 2.1 to 3.2 g kg -1 DM. With its moderate levels of lysine, methionine and taurine, ocean farmed G. tikvahiae has the potential of overcoming many nutrient deficiencies currently associated with terrestrial plant ingredients in alternative feeds for fish and shrimp.