The relationship between feed intake and gonad growth of single and stocked green sea urchin (Strongylocentrotus droebachiensis) in a raceway culture

This study provides a robust relationship between feed intake (FI), gonad growth (GG), and feed conversion ratio (FCR) of cultured adult green sea urchin Strongylocentrotus droebachiensis. Sea urchins (test diameter: ∼ 54 mm and live weight: ∼ 70 g) were collected in the wild and cultured either individually or subjected to one of three stocking densities, i.e. low 2.5 (N = 36), medium 3.7 (N = 54), or high 7.3 (N = 108) kg animal per m2. Animals were fed a prepared diet in excess for 56 days at 6.5–4.5 °C. The gonad index (GI) more than doubled during the 56 day trial. The final mean values of GI (17–18%), FI (0.3–0.4 g feed per animal per day), and FCR (∼ 3 g feed per g increase in gonad weight) were statistically similar between individual and stocked animals. Based on data from the individually cultured sea urchins, the relationship between daily FI (g feed per animal) and GG (g gonad increase per animal) could be described by the equation: GG = 0.619FI − 0.097 (R2 = 0.533, P < 0.001). In conclusion, marketable sizes of green sea urchin perform well in raceways at densities of 7–8 kg animal per m2 without adverse effects on FI, GG, and FCR.