Growth and survival of California sea cucumbers (Parastichopus californicus) cultivated with sablefish (Anoplopoma fimbria) at an integrated multi-trophic aquaculture site

In a 12-month field trial we examined the growth and survival of California sea cucumbers (Parastichopus californicus) in suspended culture underneath net pens of sablefish (Anoplopoma fimbria) at an experimental integrated multi-trophic aquaculture (IMTA) site. We tested the effects of sea cucumber size (small: 7-99 g and large: 100-565 g whole wet weight) and stocking density (12, 17, and 21 ind m− 2) on growth and survival in a completely-crossed experimental design. We also compared growth and survival of experimental animals cultured directly under the fish pens with control sea cucumbers grown ~ 250 m away from the farm. The ability of the sea cucumbers to reduce total organic carbon and total nitrogen from the sablefish faeces was also examined. Small experimental animals grew significantly faster than large experimental individuals, the former increasing in whole wet weight by 27-56% over the 12 months and the latter decreasing by 10-33% over the same period. It was concluded that stocking densities of large animals were too high to produce net positive growth. Stocking density had a significant effect on growth of both size classes, lower densities producing higher growth rates, or less negative growth rates in the case of large animals. Small sea cucumbers suspended directly below the sablefish net pens grew significantly faster than control individuals grown ~ 250 m away from the farm, which had negative growth over the 12-month period. The small sea cucumbers cultured under the net pens had a high survival rate (mean: 99.5%) and their feeding reduced the total organic carbon and total nitrogen contents of the sablefish faeces by an average of 60.3% and 62.3%, respectively, demonstrating their potential as an important organic-reducing component in IMTA. Suspending sea cucumbers below fish net pens, as opposed to growing them on the seabed, makes their collection and monitoring easier and moves them away from potential seabed predators such as sea stars. This study demonstrated that P. californicus is well suited to utilise the heavy fraction of waste from a sablefish farm while providing an additional valuable harvestable product.