Growth and mortality of the New Zealand abalone Haliotis iris Martyn 1784 cultured in offshore structures and fed artificial diets

Comparisons of growth and mortality were made over 12 months for the New Zealand abalone Haliotis iris Martyn 1784 (blackfoot paua), fed two artificial diets (Coast Biologicals and Makara) and cultured in three offshore grow-out structures: barrel, cage (a novel structure designed specifically for this study) and tube. Abalone grew significantly faster in tubes and cages (mean length increase 61 +/- 10.7 mu m and 54 +/- 5.3 mu m day(-1) respectively) than in barrels (mean length increase 39 +/- 3.31 mu m day(-1)). Abalone grown in tubes and fed a diet of Makara grew significantly faster than abalone grown in tubes and fed a diet produced by Coast Biologicals. Abalone in cages fed a diet produced by Coast Biologicals grew significantly faster than abalone in cages fed Makara. The difference in growth produced by the two diets may be related to improved food availability in cages throughout the feeding period. Mortality was high in all structures (66% of the entire experimental population) and did not differ significantly among structure and diet treatments, Mortalities were thought to be caused by a combination of shell infestations (by burrowing worms) and silty water conditions within the grow-out structures. The commercial food conversion ratio was used to compare the performance of diets within structures. Mean values ranged from 13.9 +/- 5.6 for paua grown in barrels and fed Makara to 2.9 +/- 0.0003 for abalone grown in tubes and fed Makara. It is likely that the food conversion ratio reflects a structure's ability to retain unconsumed food.