Comparison of macroalgal (Ulva and Grateloupia spp.) and formulated terrestrial feed on the growth and condition of juvenile abalone

The culture of abalone is a growth industry in Australia that primarily utilises terrestrial crops to produce formulated pellet feeds. The use of cultivated macroalgae in place of such feeds could provide for better environmental, nutritional and/or economic outcomes for this industry. However, direct comparison trials using macroalgae and formulated crop feeds are rare, and it is therefore difficult to ascertain the benefits and costs of each feed type. This study compares the benefits to growth and performance of the cultivated hybrid abalone cross (Haliotis rubra 1814 Leach and Haliotis laevigata 1808 Donovan) which was fed one of eight dietary treatments, including two commercially formulated pellet feeds and six mixed macroalgae dietary treatments. Macroalgae dietary treatments comprised the three macroalgae species Grateloupia turuturu Yamada, Ulva australis Areschoug and/or Ulva laetevirens Areschoug. Four replicate tubs, each containing 40 juvenile abalone (10-15 mm), were used to test each dietary treatment over a 12-week period. Macroalgae dietary treatments provided for significantly higher specific growth rates of abalone compared to formulated feeds, by orders of magnitude, for both length (> 0.2 % compared to < 0.1 % day(-1), F (7, 31) = 22.3, p < 0.0001) and weight (from < 0.4 to > 0.8 % day(-1), F (7, 31) = 24.4, p < 0.0001). In addition, abalone health and condition increased, and the proximate composition of abalone tissue had a higher carbohydrate/protein ratio, higher ash content and lower lipid content. These findings suggest that the juvenile abalone may benefit from macroalgae diets in comparison to two formulated feeds as a result of optimal proximate composition of the algae biomass and improved condition of the abalone.