Digestive physiology and utilisation of macroalgae as feed for Australian abalone.

Author: Matthew Bansemer

Bansemer, Matthew, 2015 Digestive physiology and utilisation of macroalgae as feed for Australian abalone., Flinders University, School of Biological Sciences

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Greenlip (Haliotis laevigata) and hybrid (H. laevigata × H. rubra) abalone are extensively farmed marine gastropods, and primarily grown in land-based systems throughout southern Australia. Limited understanding of nutritional requirement impedes Australian abalone aquaculture, which forms the main thrust of this thesis. The main objectives of this thesis were to: (i) understand the interaction between age, water temperature and dietary protein on abalone growth and digestive physiology; and (ii) provide a fundamental understanding on the effective use of macroalgae as feed for cultured Australian abalone.

There is a demand to introduce multi-diet feeding strategies for greenlip abalone by optimising the dietary protein level for each age class and water temperature throughout the production cycle. However, the optimal dietary protein level for greenlip abalone in the production cycle is not clear. Abalone at 20 °C exhibited significantly superior growth, protein deposition, and feed conversion ratios (FCR) to those at 14 °C. Dietary protein level did not affect abalone growth. Faster growing animals at 20 °C up-regulated feed intake when fed low protein diets to increase protein intake and maximise growth. We recommend that greenlip abalone be fed at ~35% dietary protein at 20 °C. In contrast, there were no apparent benefits by feeding high protein diets to abalone at 14 or 17 °C. We recommend that 6-month old greenlip abalone be fed with 29% dietary protein at <17 °C to improve growth and feed efficiency.

Diet changes could alter digestive enzyme activities, but the response of digestive enzymes to the level of protein in formulated diets is not clearly understood. The digestive enzyme activities of juvenile (1-year old) and sub-adult (2-year old) greenlip abalone fed crude protein from 24 to 36% at 14, 18 and 22 °C were investigated. Trypsin, α-amylase and lipase activities were influenced differently by abalone age, water temperature and dietary protein levels. The trypsin activity down-regulation by age suggests that dietary protein for 2-year-old abalone could be lower than for 1-year old greenlip abalone.

Although greenlip abalone are fed formulated diets on-farm, in the wild they predominantly consume macroalgae. In Australia, feeding macroalgae to greenlip abalone was previously limited due to the prohibition of wild macroalgae collection on mainland Australia. Recently however, there has been interest to develop an Australian macroalgae aquaculture industry, which would be capable of supplying high quality feed for farmed abalone. While Ulva sp. stimulated abalone feeding activity, animals had lower nutrient intake than those fed formulated diets, due to the high moisture content in fresh algae.

To improve protein density, the effect of nitrogen enrichment and the type of macroalgae species on the growth and feed utilisation of greenlip abalone were investigated. Abalone fed G. cliftonii outperformed those fed Ulva sp., but the benefit of nutrient enrichment on macroalgae was species-dependent. While abalone fed enriched Ulva sp. exhibited superior growth to those fed non-enriched Ulva sp., abalone fed non-enriched and enriched G. cliftonii exhibited similar growth. Abalone fed non-enriched G. cliftonii had higher protein deposition and protein efficiency ratio than those in other dietary treatments. Feeding Ulva sp. and G. cliftonii together had a positive synergistic effect on abalone growth. However, abalone fed commercial formulated diets exhibited faster growth than those fed either type of fresh macroalgae.

While feeding fresh macroalgae to abalone led to sub-optimal growth, dried macroalgae meals were promising ingredients for abalone diets. Abalone fed Gracilaria sp. meal. outperformed those fed Ulva sp. meal. Abalone fed 5% Gracilaria sp. meal or Ulva sp. meal exhibited superior growth to abalone fed 0%. Increasing dietary Gracilaria sp. to >10% led to further growth improvements, but reduced protein and energy retentions. In contrast, abalone fed 10 and 20% Ulva sp. exhibited similar growth to those fed 0 and 5% Ulva sp. We recommend a dietary inclusion of 10% Gracilaria sp. or 5% Ulva sp. to improve abalone growth.

This research provides new knowledge of the protein requirements in juvenile greenlip abalone. The changes of digestive enzyme activities in abalone depend on age, water temperature and dietary protein. Furthermore, this study indicates that greenlip abalone fed fresh macroalgae had slower growth compared with those fed formulated diets, but inclusions of dried macroalgae improve abalone growth. This research contributes to the improvement of dietary formulations and improved abalone production in Australia.

Keywords: Greenlip abalone, Hybrid abalone, macroalgae, protein, digestive physiology

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2015
School: School of Biological Sciences
Supervisor: Prof. Jian Qin