Feeding Preferences and the Nutritional Value of Tropical Algae for the Abalone Haliotis asinina

Understanding the feeding preferences of abalone (high-value marine herbivores) is integral to new species development in aquaculture because of the expected link between preference and performance. Performance relates directly to the nutritional value of algae – or any feedstock – which in turn is driven by the amino acid content and profile, and specifically the content of the limiting essential amino acids. However, the relationship between feeding preferences, consumption and amino acid content of algae have rarely been simultaneously investigated for abalone, and never for the emerging target species Haliotis asinina. Here we found that the tropical H. asinina had strong and consistent preferences for the red alga Hypnea pannosa and the green alga Ulva flexuosa, but no overarching relationship between protein content (sum of amino acids) and preference existed. For example, preferred Hypnea and Ulva had distinctly different protein contents (12.64 vs. 2.99 g 100 g−1) and the protein-rich Asparagopsis taxiformis (>15 g 100 g−1 of dry weight) was one of the least preferred algae. The limiting amino acid in all algae was methionine, followed by histidine or lysine. Furthermore we demonstrated that preferences can largely be removed using carrageenan as a binder for dried alga, most likely acting as a feeding attractant or stimulant. The apparent decoupling between feeding preference and algal nutritive values may be due to a trade off between nutritive values and grazing deterrence associated with physical and chemical properties

Effect of short-term immersion of Kappaphycus alvarezii (Doty) Doty in high nitrogen on the growth, nitrogen assimilation, carrageenan quality, and occurrence of “ice-ice” disease

Short-term immersion of Kappaphycus alvarezii (Doty) Doty in a high-nitrogen-containing medium was tested to increase growth, improve the quality of carrageenan, and decrease “ice-ice” disease occurrence. Tank-reared Kappaphycus were used as explants. Growth, nitrogen assimilation, carrageenan quality, and occurrence of ice-ice disease of enriched (E/N) K. alvarezii were determined. E/N and un-enriched (control) K. alvarezii were planted inside net cages in the sea. Nitrogen assimilation was monitored to determine if nitrogen was incorporated in the tissues after 12 h. Total thallus nitrogen of K. alvarezii doubled after immersion in high nitrogen. Growth rate and carrageenan yield of E/N K. alvarezii were significantly higher than those of the control. Gel strengths of E/N and the control were not significantly different. Ice-ice disease occurrence was significantly higher in the control than the enriched seaweeds. Short-term immersion of K. alvarezii in a high-nitrogen medium before outplanting increased growth rate and decreased the occurrence of “ice-ice”.Acknowledgement is due to the Australian Centre for International Agricultural Research (ACIAR SMAR/2008/025)