World Aquaculture Magazine - March 2021

WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2021 65 marine invertebrates (Delacroix et al. 2013). However, the oxidizing species react by creating reactive subspecies that are potentially harmful to the aquatic environment (Reiser et al. 2011). UV irradiation is therefore considered to be an effective alternative to ozonation and chlorination for the inactivation of pathogens in aquaculture. Although this process has the advantage of not generating disinfection byproducts, a UV system is not totally effective for the treatment of gametes or oyster larvae. Moreover, the effectiveness of pathogen removal by UV is linked to the turbidity of water (Li et al. 2000, Gullian et al. 2012). The objective of this study was to evaluate the efficiency of ultrafiltration for the retention of spermatozoa and oocytes of Crassostrea gigas oysters in the case of continuous release at low concentrations, or intermittent, accidental release at high concentrations, as both may occur in effluents from oyster hatcheries. The viability of these species was studied after treatment by flow cytometry and microscopic analysis. Study Methods Gamete treatment trials were conducted at the Ifremer station in Bouin, France, which is continuously supplied with seawater from the Atlantic Ocean through Bourgneuf Bay. Over the six months of tests, the average quality of incoming seawater was: turbidity - 4.5 NFU, salinity - 33.5 g/L, chlorophyll a - 4.5 µg/L and pheopigments - 0.7 µg/L. Ultrafiltration experiments were performed with two types of discharges: 1) chronic, corresponding to a continuous release of small quantities of gametes and 2) accidental, corresponding to a short-term release of a high quantity of gametes during spontaneous spawning of all individuals in the same spawning event or during fertilization, during which a surplus of gametes can be released in the effluents. These two types of effluents have gamete I n aquaculture, management of incoming water and effluents requires use of seawater treatment and disinfection processes, especially in the context of increasing sanitary crises affecting aquatic animals. In particular, shellfish farming faces two challenges: 1) upstream degradation of coastal water quality, principally related to the presence of pathogens responsible for high mortality in juveniles and adults and 2) preservation of the environment and biodiversity through production of native or exotic oysters in commercial hatcheries. Farm biosecurity is therefore a priority for many professionals who have to deal with new environmental regulations. In this context, development of a reliable process leading to complete removal of specific biological materials must be studied. This is the case with triploid oysters that grow faster than diploid oysters and have a constant flavor quality throughout the year because they do not enter gametogenesis. Production of tetraploid shellfish imposes a risk for marine biodiversity. Indeed, if such biological material was released into the environment, the undesirable sterilization of wild oysters is a potential outcome. The elimination of gametes (spermatozoa and oocytes) from the effluents of shellfish farms likely to produce them is necessary to reduce the risk. The main processes effective at controlling various pathogens encountered in aquaculture are chemical oxidation, UV radiation, electrolytic methods and heat (Kasai et al. 2002, Kasai et al. 2011, Sharrer et al. 2005). Membrane processes are used to treat supply water (Szmukala and Szaniawska 2009) or eliminate toxic microalgae (Castaing et al. 2011). Only a few studies have evaluated the treatment performance of removing biological material from the effluent of shellfish hatcheries. The effectiveness of oxidation by chlorine, ozone and UV radiation— the most widely used processes for disinfection of seawater —have been studied for the inactivation of biological material of oysters Crassostrea gigas (Stavrakakis et al. 2017). Chlorine is considered to be a potential spermicide for various Removal of Oyster Gametes from Hatchery Effluents by Ultrafiltration Clémence Cordier, Christophe Stavrakakis, Béatrice Dupuy, Mathias Papin, Patrick Sauvade, Franz Coelho and Philippe Moulin FIGURE 1. Experimental plan to generate chronic and accidental releases of oyster gametes. Production of tetraploid shellfish imposes a risk for marine biodiversity. Indeed, if such biological material was released into the environment, the undesirable sterilization of wild oysters is a potential outcome. The elimination of gametes (spermatozoa and oocytes) from the effluents of shellfish farms likely to produce them is necessary to reduce the risk. The main processes effective at controlling various pathogens encountered in aquaculture are chemical oxidation, UV radiation, electrolytic methods and heat. ( C O N T I N U E D O N P A G E 6 6 )