Effect of larval density on growth and survival of the Pacific oyster Crassostrea gigas in a recirculation aquaculture system

doi:10.1016/j.aquaculture.2021.736667

Aquaculture

Volume 540, 15 July 2021, 736667

https://doi.org/10.1016/j.aquaculture.2021.736667 Get rights and content

Highlights

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We describe the feasibility of producing larvae at recirculation aquaculture system (RAS).
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We determined the effect of stocking density on larval growth and survival.
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We found it is possible to culture larvae between 50 and 100 larvae mL⁻¹ in the RAS.

Abstract

The present study determined the effect of larval stocking density on larval yield (number of live larvae at the end of the experiment), competent larvae (number of live larvae at the end of the experiment retained on a sieve with mesh size of 236 μm (1st experiment) and 239 μm (2nd experiment)), and larval shell length of Crassostrea gigas in a recirculation aquaculture system (RAS). Two experiments were performed at different larval stocking densities: 50, 100 and 150 larvae mL⁻¹ (1st experiment) and 50, 75 and 100 larvae mL⁻¹ (2nd experiment). We used 250 L tanks and a randomized block design with three replicates per treatment (larval density). The physical and chemical parameters of the water were stable in all treatments during the experimental period. Our results demonstrated the feasibility of producing Crassostrea gigas larvae in a RAS at larval densities of 50 and 75 larvae mL⁻¹; however, rearing larvae at densities of 50 larvae mL⁻¹ resulted in the best growth and highest proportion of competent larvae. This RAS approach could be used to optimize larval rearing and improve both the resource efficiency and profitability of commercial hatcheries.

Introduction

The Pacific oyster Crassostrea gigas (Thunberg, 1793) is the bivalve species of greatest global commercial aquaculture interest because of its high productivity and wide tolerance to environmental conditions (Mann et al., 1991; Orensanz et al., 2002; Ruesink et al., 2006) and, therefore, this species has been introduced in several countries (for reviews, see Nerhing, 2006; Miossec et al., 2009). Its annual world production was approximately 643,000 tons in 2018 (FAO, 2020), making an important contribution to the world aquaculture industry. Due to the rapid worldwide expansion in the cultivation of C. gigas, it is necessary to establish new technical procedures for hatchery seed production, making them more efficient and enabling production in regions where collection of natural seed is not possible (Helm and Millican, 1977; Quayle, 1988; Collet et al., 1999). In this sense, bivalve larval hatcheries can be vitally important in creating opportunities for genetic improvement of stocks and providing a reliable source of seed for farmers throughout the year.

Techniques for the culture of bivalve larvae began to be developed in the 1960's with the use of static systems for culturing Crassostrea virginica (Loosanoff and Davis, 1963) and Ostrea edulis (Walne and Spencer, 1974), and later were used worldwide for other species (for reviews, see Castagna, 1983; Utting and Spencer, 1991; Robert and Gérard, 1999; Helm et al., 2004; Gosling, 2015). Since the 1990's, open-flow systems have made it possible to increase the density of larval cultures and reduce the use of physical laboratory space. The first cultures of bivalve in an open-flow system were carried out with the species Pinctada margaritifera (Southgate and Ito, 1998) and Pecten maximus (Robert and Gérard, 1999; Andersen et al., 2000), and were later evaluated for other species (e.g., scallops: Robert and Gérard, 1999; Andersen et al., 2000; Sarkis et al., 2006; Magnesen et al., 2006; and oysters: Rico-Villa et al., 2006, Rico-Villa et al., 2008; Reiner, 2011; Suneja et al., 2014). More recently, studies have sought to use recirculating aquaculture systems (RAS), aiming to further optimize production by using high larval densities and minimal water consumption, allowing greater control of culture conditions and improving the management of waste streams (Badiola et al., 2012; Ebeling and Timmons, 2012; Murray et al., 2014). Although the number of RAS studies for culturing bivalve larvae are limited (e.g. Venerupis corrugata, Joaquim et al., 2016; Crassostrea virginica, Congrove, 2012; Kuhn et al., 2013; C. gigas, Asmani et al., 2016, Asmani et al., 2017; Crassostrea angulata, Qiu et al., 2015, Qiu et al., 2017; Pecten maximus, Magnesen and Jacobsen, 2012; and Argopecten purpuratus, Merino et al., 2009), the reported larval growth and survival rates are promising.

One of the major problems currently encountered in the production of bivalve mollusks in a RAS is to define an appropriate protocol to provide satisfactory rearing conditions in terms of: i. temperature; ii. frequency of feeding; iii. algal concentration; iv. larval handling; v. density of larval storage; and vi. water flow. Among these factors, larval stocking density is an important and easily manipulated cultivation parameter (Dahlhoff, 2004; Liu et al., 2006; Takahashi and Muroga, 2008). High stocking densities can adversely affect feeding rates, oxygen consumption and growth efficiency (MacDonald, 1988; Gireesh and Gopinathan, 2008; Velasco and Barros, 2008). The effects of stocking density on larval development and survival have been studied for several species of bivalves, including cockles (Hurley and Walker, 1996; Walker et al., 1998; Liu et al., 2006; Yan et al., 2006; Gireesh and Gopinathan, 2008; Liu et al., 2010), mussels (Brenko and Calabrese, 1969; Langdon and Önal, 1999), oysters (Doroudi and Southgate, 2000; O'Connor and Lawler, 2004; Saucedo et al., 2007) and scallops (Gruffydd and Beaumont, 1972; Lu and Blake, 1996; Rupp and Parsons, 2004; Gouda et al., 2006).

In bivalve hatcheries using the static production system, the larvae are grown at stocking densities between 1 and 20 larvae mL⁻¹, depending on age and species (for reviews, see Robert and Gérard, 1999; Helm et al., 2004; Gosling, 2015). In continuous open-flow system studies, there is generally an increase in larval concentrations to between 5 and 200 larvae mL⁻¹, but the most common stocking density is 50 larvae mL⁻¹ (Rico-Villa et al., 2008; Costa et al., 2015). Different species of shellfish have different growth performances when maintained at the same density in continuous open-flow culture systems (Magnesen et al., 2006; Sarkis et al., 2006; Rico-Villa et al., 2008; Costa et al., 2015); however, there have been few studies that have determined the effect of stocking density in RAS larval cultures (Asmani et al., 2017). The main objective of this study was to assess the effect of stocking density on the growth, survival and settlement competency of larval C. gigas reared in commercial-scale RAS.

Section snippets

Local of study and recirculation system

This study was carried out on Laboratory of Marine Mollusks, Department of Aquaculture, Federal University of Santa Catarina, Florianópolis, Brazil, between 25 October to 14 November 2017 (1st experiment) and between 2 December to 22 December 2017 (2nd experiment).

The RAS (Fig. 1, Fig. 2, Fig. 3) used in this study consisted of nine cylindrical-conical white fiberglass larval culture tanks (250 L each tank; Fig. 1, n° 1), nine microalgae containers (100 L each; positioned next to the larval

Results

In the first experiment, significant differences in larval growth in shell lengths were observed at the 14th and 17th day of culture between densities of 50 (11.82 μm day⁻¹) and 150 larvae mL⁻¹ (9.03 μm day⁻¹; Figs. 4A, B). In contrast, in the second experiment the only significant difference in shell growth in lengths occurred on the sixth day of culture, between larvae reared at densities of 50 and 100 larvae mL⁻¹ (20.79 and 19.04 μm day⁻¹, respectively; Figs. 4C, D).

The greatest larval yield

Discussion

The results of this study demonstrated the feasibility of the use of a commercial-scale RAS for the production of C. gigas oyster larvae at high stocking densities using a zero-water exchange. Our results showed that stocking densities of 50 larvae mL⁻¹ resulted in higher survival and competent larvae; therefore all stocking densities studied the RAS maintained optimal physical-chemical parameters of the culture water. The higher RAS densities were likely only possible due to continuous

Conclusion

The results of this study demonstrate the feasibility of producing Crassostrea gigas larvae in a RAS at larval densities of 50 and 75 larvae mL⁻¹. However, larval rearing with densities of 50 larvae mL⁻¹ is recommended, as the best growth rate and larval yields were observed in this treatment.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors are grateful for the financial support received from the Ministério da Pesca e Aquicultura (MPA) grant n° 23080.070481/2013 and from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), through the Ciência do Mar 2 project, grant n° 1969/2014. They also thank the Concelho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the PhD scholarship awarded to Cassio de Oliveira Ramos and for the Research Productivity scholarship awarded to Dr. Claudio

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