Assessing compatibility for low trophic IMTA: Growth performance of hatchery reared Holothuria arguinensis juveniles as extractive species for Paracentrotus lividus in a co-culture setting

Aquaculture techniques for rearing of the sea cucumber, Holothuria arguinensis (Koehler and Vaney, 1906), have been developed during the last few years. However, growth of hatchery-reared juveniles of this species, particularly during the juvenile stage, is still slow. Although monospecific rearing techniques have been optimized, integrated multi-trophic aquaculture (IMTA) might present itself as an ecologically viable means to improve H. arguinensis production. This rearing approach can simultaneously improve water quality parameters and mitigate ecological impacts by waste bioremediation. Utilizing the sea urchin Paracentrotus lividus (Lamark, 1816) as the fed species, IMTA compatibility and growth performance of both species were assessed for the first time in this rearing model, through three different stocking density ratios between sea urchins (su) and sea cucumbers (sc): D1 = 30su:10sc; D2 = 20su:20sc; D3 = 10su:30sc. Over a 3-month rearing period, growth performances were collected every 21 days by measuring the individual weights and lengths of sea urchin and sea cucumber specimens. At the end of the trial, all sea cucumbers experienced significant growth, in terms of Specific Growth Rate (% day −1 ). Among the three experimental conditions, sea cucumbers in D1 registered the highest weight gain, length gain, and survival rate at the end of the trial, conversely to D3 that displayed the lowest growth and survival rates. However, regardless of stocking density, all treatments displayed an overall higher SGR compared to previous assessments on monospecific rearing of H. arguinensis juveniles. • Cultured Holothuria arguinensis had their suitability as extractive species for sea urchins determined under three different stocking ratios. • The lowest stocking of sea cucumbers (30su:10sc) displayed the highest growth. • Sea cucumbers, under all stocking ratios, displayed higher growth than any H. arguinensis of similar size reared in a monoculture setting, so far. • All sea urchins displayed continuous growth in all treatments.