On-growing cultured abalone (Haliotis iris) in northern New Zealand

Hatchery-reared paua (Hallotis iris) were held for 100 days under two experimental regimens in northern New Zealand to determine the best system for on-growing. The paua were kept in small baskets suspended in larger tanks, which allowed assessment of growth and mortality with three different diets (two artificial and one natural) and three different stocking densities. For all treatments, paua held inside a building with constant darkness showed significantly better growth than did those kept outside under natural (although shaded) light. Shell increments were 20-30% greater inside, but weight gains were only half this. Paua fed either of the artificial foods consistently grew better than did those fed dried Gracilaria, and growth was always better at lower stocking densities. However, variable and often high mortality (40-50%), both inside and outside, made it difficult to use the experimental results on growth to determine optimal on-growing conditions. The implications of this for further experiments and for designing appropriate systems for on-growing paua in the warm waters of northeastern New Zealand are discussed.