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, 24°C) to fall (November, 13°C) 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 pla-teaued. Nitrogen increased from 22 ± 1 g kg-1DM in August to 39 ± 3 g kg-1DM in October (p < 0.001). Protein increased from 107 ± 13 g kg-1DM in August to 196 ± 5 g kg-1DM in November (p < 0.001). With two exceptions, amino acid concen-trations 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-1CP and 18 ± 1 g kg-1CP, respectively. Histidine was underrepresented among essential amino acids and averaged 13 ± 1 g kg-1CP. Taurine ranged from 2.1 to 3.2 g kg-1DM. With its moderate levels of lysine, methionine and taurine, ocean farmed G. tikvahiaehas the potential of overcoming many nutrient deficiencies currently associated with terrestrial plant ingredients in alternative feeds for fish and shrimp.