Reproductive cycle of a non-native oyster, Crassostrea gigas, in the Adriatic Sea

Abstract

The Pacific oyster Crassostrea gigas was introduced for the aquaculture purposes in many different parts of the world. However, the species has never been officially introduced for commercial farming in the Croatian part of the Adriatic Sea. Interestingly, in the 1970s, the Pacific oyster has been reported in the natural habitats of the Lim Bay, in northern Adriatic Sea. Although the species was recorded there, there is a lack of knowledge about its biology and ecology in this region, including a reproductive cycle. Information on the reproductive biology of non-indigenous species in new areas is crucial for prediction of their future survival and possible spread in invaded habitats. In this study, we provide the first data on the reproductive biology of the Pacific oyster in the Adriatic Sea, the northernmost part of the Mediterranean Sea. Quantitative and qualitative methods of gonad tissue analysis were conducted, and effects of environmental conditions on the gametogenesis were evaluated during two reproductive cycles. Our study confirmed that environmental conditions in the Lim Bay were favourable for the reproduction of the species. The Pacific oyster reproduced once per year and had a prolonged spawning period. Water temperature was the main factor affecting gonad development and oocyte size, while chlorophyll a concentration had an impact on the oocyte development in terms of their size.

Reproductive Biology and Spawning Pattern of Oyster Magallana bilineata in Mengkabong Bay, Sabah, Malaysia

“…The Magallana bilineata population in Mengkabong Bay was found to be female-biased at a ratio of 1:2.36. These findings are consistent with those of several other Crassostrea species, including Crassostrea (M.) saidii, C. brasilliana, C. cortezieensis, C. gigas, and C. rhizophorae (Castilho-Westphal et al, 2015;Ezgeta-Balić et al, 2020;Antonio et al, 2021;Barman et al, 2022). Conversely, several Crassostrea species have been reported to be malebiased (Rodríguez-Jaramillo et al, 2008) or have similar or almost equal sex ratios (Castaños et al, 2009;Vaschenko et al, 2013;Dridi et al, 2014).…”

“…The sections were then mounted with DPX and examined under an inverted microscope (CKX41, Olympus) at 40x to 100x magnifications to determine the sex ratio and gonad developmental stages. Six stages (inactive, early active, late active, ripe, spawning, and spent) were identified following the scale proposed by Ezgeta-Balić et al (2020), and the numerical values and descriptions of the six stages for male and female gonads are presented in Table 1 and Fig. 3 and Fig.…”

Triploid Pacific oysters exhibit stress response dysregulation and elevated mortality following marine heatwaves

“…Samples were embedded in paraffin, stained with hematoxylin and eosin, sectioned, and imaged at 4x, 10x, and 40x magnification. Images of diploid and triploid gonad sections were assigned to reproductive stages in accordance with ploidy-specific metrics as outlined by (Ezgeta Balic et al, 2020) and (Matt & Allen, 2021), respectively. Gonad was assessed as either resting (stage 0), within an early (stage 1) or late growth stage (stage 2), mature (stage 3), spawning (stage 4), or unknown.…”

Annual gametogenic phenology of oyster, Magallana bilineata (Röding, 1798) collected from the west coast of Moheshkhali Island, Cox's Bazar, Bangladesh

“…In contrast, several other species of Megallana (= Crassostrea ), including M. brasilliana , M . cortezieensis , M. gigas , M. irhizophorae , and M. aidii , have been reported to have a female bias [ 22 , 30 , 31 ]. However, some of these species have been reported with either equal sex ratios [ [32] , [33] , [34] ] or male-biased ratios in different countries [ 35 ].…”