Author: Thanh Hoang Hai

Hoang Hai, Thanh, 2017 THE EFFECTS OF DIET AND WATER TEMPERATURE ON THE COLOUR OF AUSTRALIAN GREENLIP ABALONE (Haliotis laevigata Donovan), Flinders University, School of Biological Sciences

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The Greenlip abalone Haliotis laevigata is a commercially important species for aquaculture in Australia. It is mainly farmed in land-based systems using formulated feeds but the colour of farmed abalone fed a formulated diet is different compared to their wild counterparts. Wild greenlip abalone fed algae typically have a green lip, yellow foot and a variety of shell colours, whereas cultured abalone fed a formulated diet have a milky lip, brown foot and light green shell. The colour of abalone, along with texture, size and taste, is an important trait affecting marketability and consumer preference. The loss of abalone’s natural colour due to the introduction of a formulated feed suggests a need for pigment supplementation via the inclusion of macroalgae, commercial synthetic pigments or other compounds to abalone feed. This thesis evaluates the effects of diet and water temperature on the colour of greenlip abalone shell, foot and lip, and pigment deposition in whole tissue. This thesis includes four data chapters (2, 3, 4 and 5).

Chapter 2 addresses colour change of the foot and shell in abalone fed various fresh macroalgae. The 1-year-old abalone fed either fresh Ulva sp. or fresh Gracilaria cliftonii developed a yellow coloured foot. Abalone developed a brown shell when fed fresh G. cliftonii, but exhibited a light green shell when fed fresh Ulva sp. or a commercial diet. Although chlorophyll a and zeaxanthin were the dominant pigments found in fresh Ulva sp. and fresh G. cliftonii, respectively, β-carotene was the main pigment in the whole tissue of abalone when fed either species of fresh macroalgae. Nutrient (nitrogen) enrichment of the macroalgae did not significantly affect pigment content in both macroalgae and the whole abalone tissue, and had little impact on shell and foot colour. The shell colour of abalone fed 3% dried Spirulina sp. was yellow-brown, while the foot was bright yellow when 10% of enriched dried Ulva sp. meal was included in the diet. Chlorophyll a was the main pigment in the diets of dried Spirulina sp. and dried Ulva sp., but the whole tissue of abalone fed those dried algae contained β-carotene as the principal pigment.

In Chapter 3, abalone fed >5% dried G. cliftonii meal developed a red/brown colour on the shell and the increased inclusion of algal meal resulted in a darker brown shell. Additionally, when abalone were fed >10% G. cliftonii meal, the lip became green. However, abalone exhibited a light green shell, milky lip and brown/darker foot when fed a diet with up to 20% Ulva sp. meal, similar to those fed the control or commercial diet. Although zeaxanthin was the major pigment in all the diets containing dried G. cliftonii, and chlorophyll a was the principal pigment in the diet containing >10% Ulva sp., β-carotene was the dominant pigment in the tissue of abalone fed these diets and its content increased significantly with the level of macroalgae inclusion.

In Chapter 4, the foot colour of 3-year-old abalone was significantly influenced by diet and water temperature, while the lip and shell colour were less affected. The foot of abalone fed enriched fresh Ulva was light gold in colour, whereas abalone fed the 30% Ulva sp. meal or the commercial diet had a dark brown foot. Abalone cultured at 22 °C had a darker brown foot than those at 26 °C. The content of β-carotene was significantly higher in abalone fed enriched fresh Ulva sp., than those fed other diets. Abalone cultured at 26 °C had a significantly lower amount of β-carotene than those at 22 °C.

In Chapter 5, the supplementation of the commercial synthetic carotenoid, astaxanthin (0.05, 0.1 and 0.2 g kg-1), and a free amino acid, tyrosine (10, 15 and 20 g kg-1), in the formulated diet, did not significantly affect the colour and pigment deposition in the whole abalone tissue.

Overall, the results of this project indicate that the shell, foot and lip colour of greenlip abalone can be modified by feeding fresh red algae or dried red algae supplements in the formulated diet. Water temperature had a significant influence on foot colour only. β-carotene was the predominant pigment in the whole tissue of abalone fed fresh or dried macroalgae inclusion in formulated diet. Greenlip abalone were unable to utilise synthetic astaxanthin or the free form of the amino acid, tyrosine. This thesis expands our knowledge on the factors that regulate colour change in abalone and provides practical approaches to change abalone colour through diet and water temperature manipulation.

Keywords: abalone, colour, macroalgae, Ulva sp., Gracilaria cliftonii, astaxanthin, tyrosine, pigmentation

Subject: Biology thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Biological Sciences
Supervisor: Prof. Jian Qin