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), US in 2011. Plants were harvested monthly, from summer to fall 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^sup -1^ DM in August to 39 7plusmn; 3 g kg^sup -1^ DM in October. Protein increased from 107 7plusmn; 13 g kg^sup -1^ DM in August to 196 ± 5 g kg^sup -1^ DM in November. 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^sup -1^ CP and 18 ± 1 g kg^sup -1^ CP, respectively.