Growth and feed utilisation of greenlip abalone (Haliotis laevigata) fed nutrient enriched macroalgae

Wild greenlip abalone predominantly consume macroalgae, but are fed formulated diets under culture conditions. This study aims to (i) investigate the effect of nutrient enrichment (non-enriched and enriched) and fresh macroalgae type (Ulva sp., Gracilaria cliftonii, and an equal combination of Ulva sp. and G. cliftonii) on the growth and feed utilisation of greenlip abalone and (ii) compare the performance of abalone fed fresh macroalgae to those separately fed either one of the three commercial formulated diets. Abalone were fed to excess at 16:00 h daily, and uneaten feed was collected the following morning. Nutrient enrichment increased the protein level for Ulva sp. and G. cliftonii from 5.3 to 27.7% and 12.9 to 38.1%, respectively. The growth of abalone fed G. cliftonii was superior to animals fed Ulva sp. The effect of enrichment was macroalgae species-dependent. While abalone fed enriched Ulva sp. exhibited superior growth to those fed non-enriched Ulva sp., animals fed non-enriched and enriched G. cliftonii exhibited similar growth. However, abalone fed non-enriched G. cliftonii had superior apparent protein deposition and protein efficiency ratio, compared to animals fed enriched G. cliftonii. Feeding an equal mix of Ulva sp. and G. cliftonii had a positive synergistic effect on abalone growth, compared to animals fed mono-specific algae. Abalone fed each commercial diet exhibited improved growth and feed utilisation compared to animals fed fresh macroalgae. The results of the current study suggest that the use of fresh G. cliftonii as a source of carbohydrates may spare protein when feeding formulated diets to abalone. When formulated diets are unavailable or are inappropriate to feed abalone, a mix of enriched Ulva sp. and G. cliftonii may be used. However, feeding fresh macroalgae alone to cultured greenlip abalone should be avoided, if growth is the parameter of interest and we recommend that commercial formulated diets be fed to cultured greenlip abalone. Statement of relevance: Abalone diet development with fresh macroalgae.