Martínez-Fernández, Erika (2007) Use of tropical microalgae species as food for pearl oyster (Pinctada margaritifera L.) larvae. PhD thesis, James Cook University.

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Abstract

The most famous round pearls of the world come from pearl oysters of the genus Pinctada; 'south-sea pearls' are cultured using the silver- or gold-lip pearl oyster, Pinctada maxima, and 'black pearls' are cultured from the black-lip pearl oyster, P. margaritifera. Marine pearl culture is one of the most valuable aquaculture industries in the world with an estimated value of $US475 millions. P. maxima is the basis of Australian pearl industry while P. margaritifera supports cultured pearl industries in southern Japan and the Pacific island nations of French Polynesia and Cook Islands. In French Polynesia, pearl production has an annual value of US$170 millions and, not surprisingly, other nations across the Pacific have shown interest in developing similar industries. The usual way to obtain oysters for pearl farms in Polynesia is by collection of wild spat (or juveniles), activity that relies entirely on natural recruitment which can be unpredictable and unreliable. Hatchery production of pearl oyster is increasing in significance as a source of oyster stock for pearl production and offers many advantages over the collection of oysters from the wild. Hatchery production of pearl oysters is a relatively new field and, as such, techniques and protocols adopted are generally based on those developed for other bivalve species of commercial importance, usually of temperate origin. Much of the research on hatchery production of pearl oyster has focused on P. margaritifera and has covered aspects such as culture systems, feeding and nutrition of larvae and early nursery culture.

Microalgae culture is fundamentally important to commercial hatcheries rearing marine molluscs, since they are currently the only suitable food source. Microalgae provided to larvae during culture can affect their growth and survival. Only recently have significant numbers of tropical microalgae species become available to the aquaculture industry. However, many of these have not been assessed for their nutrient content or their nutritional value for culture animals. Microalgae of tropical origin are likely to be better suited to the culture conditions used for tropical species, such as P. maxima and P. margaritifera.

This study assessed the nutritional value of eight tropical microalgae species for P. margaritifera larvae. Each was analysed for carbohydrate, lipid and protein content as well as fatty acid and amino acid composition. Each species of microalgae was fed singly to early (D-stage veliger, Chapter 3 (section 3.3.1)) and later (umbo-stage veliger, (section 3.3.2)) P. margaritifera larvae. The results showed Pavlova sp. and P. salina to be the most nutritious of eight microalgae fed to both D-stage and umbone larvae. Relationships between the levels of various nutritional components of microalgae and resulting larval growth were determined. A significant correlation between the growth of D-stage larvae and total protein, lipid and carbohydrate contents of microalgae was found. However, for umbo-stage larvae only carbohydrate contents in microalgae was positively correlated to larval growth. Significant positive correlation between the saturated fatty acid (SFA) and polyunsaturated fatty acid (PUFA) contents of microalgae and larval growth were seen for both larval stages.

Bivalve larvae are generally fed a mixture of microalgae species in order to provide a better nutrient balance. This study assessed the more nutritious species of microalgae from Chapter 3 in binary and ternary combinations. D-stage P. margaritifera larvae were fed Pav. salina, Pavlova sp, TISO and Micromonas pusilla in binary and ternary combinations, Chapter 4 (section 4.3.1). Umbo-stage larvae were fed the best binary algae combinations (flagellates) to which one diatom species (either Chaetoceros muelleri, Chaetoceros sp. or Skeletonema sp.) was added per combination (section 4.3.2). The best two ternary algae combinations from the first experiment in Chapter 4 with Dstage larvae (flagellates only), were also used to feed umbo-stage larvae in the second experiment in Chapter 4; these were Pav. salina/ Pavlova sp/TISO and TISO/M. pusilla/Pavlova sp. Greater growth rate was shown by D-stage P. margaritifera larvae fed the ternary combination of Pavlova sp/Pav.salina/TISO followed by the binary combination of Pavlova sp./M. pusilla; however, larvae fed Pavlova sp. as a monospecific diet performed as well as those fed the combination of Pavlova sp/Pav. salina/M. pusilla. Umbo-stage larvae fed ternary combinations containing a diatom showed noticeably greater growth rates than larvae fed combinations without diatoms. The best binary and ternary microalgae combinations for umbo-stage larvae were Pavlova sp./C. muelleri and Pavlova sp./M. pusilla/Skeletonema sp., respectively. However, the growth rate of larvae fed the binary combinations of Pavlova sp./C. muelleri did not differ significantly from those of larvae fed ternary diet combinations.

Experiments in Chapters 3 and 4 identified microalgae supporting the greatest growth rates of D-stage and umbo-stage larvae of P. margaritifera. Biochemical analysis of these microalgae (Chapter 2) allowed identification of nutrients within the microalgae that correlate to good growth rates. Chapter 5 investigated the possibility that manipulation of culture conditions could be used as a means of improving (increasing) the levels of these key nutrients in microalgae. Such a development would have clear benefits in the culture of P. margaritifera larvae. TISO, Pav. salina, Pavlova sp., M. pusilla and C. muelleri were cultured under different light regimes. All microalgae tested were easy to grow. Under the culture conditions used during this experiment, photoperiods of 18 hours light and 6 hours dark (18L:6D) and continuous light resulted in greater productivity of algae cultures. Differences in proximate compositions of microalgae were not significant in terms of growth phase; however, general increases in lipid contents of microalgae between the logarithmic and stationary phase growth phases were observed as reported in similar studies. Harvesting microalgae during the stationary growth phase will provide microalgae with high lipid and protein values. Changes in fatty acid contents were species specific; however contents were not significantly different when algae were culture under each light regime.

In summary, this study is the first comprehensive assessment of the nutritional value of tropical microalgae species for pearl oyster larvae and the first to relate larval growth rates and survival to the nutrient composition of microalgae. This study has identified species of microalgae that are highly nutritious for P. margaritifera larvae, and the nutrients that impart high nutritional value to them. Assessment of growth rates and changes in the biochemical compositions of microalgae cultures of different ages and under varying culture conditions will allow tropical microalgae to be cultured according to a regime which not only maximizes their productivity, but optimizes the nutritional composition for P. margaritifera larvae. On this basis, the results of this study provide a basis for development of more effective larval culture techniques for P. margaritifera and larvae of different ages.

Item ID:	64387
Item Type:	Thesis (PhD)
Keywords:	larvae; larval growth; pearl oyster; tropical microalgae; biochemical composition; fatty acid; microalgae; nutritional; pearl oyster; Pinctada margaritifera
Related URLs:	https://researchonline.jcu.edu.au/2467/ https://researchonline.jcu.edu.au/3884/
Copyright Information:	Copyright © 2007 Erika Martínez-Fernández.
Additional Information:	Two publications arising from this thesis are stored in ResearchOnline@JCU, at the time of processing. Please see the Related URLs. The publications are: Martínez-Fernández, Erika, and Southgate, Paul C. (2007) Use of tropical microalgae as food for larvae of the black-lip pearl oyster Pinctada margaritifera. Aquaculture, 263 (1-4). pp. 220-226. Martínez-Fernández, Erika, Acosta-Salmon, Héctor, and Southgate, Paul C. (2006) The nutritional value of seven species of tropical microalgae for black-lip pearl oyster (Pinctada margaritifera L.) larvae. Aquaculture, 257 (1-4). pp. 491-503.
Date Deposited:	18 Sep 2020 03:15
FoR Codes:	07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070405 Fish Physiology and Genetics @ 100%
SEO Codes:	83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830104 Aquaculture Oysters @ 100%
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