Performance and Fecundity of Triploid Eastern Oysters Crassostrea virginica (Gmelin, 1791) and Challenges for Tetraploid Production

Abstract

ABSTRACT The goal of this study was to initiate a program for producing Florida tetraploid founders to meet the needs of the fast-growing oyster farming industry in the Gulf of Mexico. The objectives were to: (1) produce chemically induced triploids originated from Florida wild stocks and (2) screen and identify triploid females for induction of tetraploid founders. By use of Florida wild stocks from different locations, chemically induced triploids were produced in three spawn groups. Compared with diploid siblings, triploids at juvenile stages did not show significant fast growth (shell metrics and body weight) in every group, but at 1-y-old in spawning season did show significantly faster growth (P < 0.0001) than their diploid siblings. Among triploids, the occurrence of female averaged 1.66% (43 out of 2,597 triploids), ranging from 0.68%, 1.2%, and 4.26% in the three spawn groups. Oocytes from these 43 triploid females averaged 214,715 per female ranging from <100 to 1,800,000. Flow cytometry analysis of gonad from the nonfemale triploids (n = 186) showed five types of ploidy composition. A majority of these nonfemale triploids (66.1%) showed 3n only, indicating no gametogenesis occurred, and other different ploidy compositions showed initiation of gametogenesis with different chromosome segregations. Tetraploid induction was conducted by fertilizing the oocytes from triploid females with sperm from diploid males followed by polar body inhibition. The fertilization varied greatly ranging from 12% to 91%, and survival to D-stage swimming larvae ranged from 0% to 24%. Ploidy of pooled D-stage larvae indicated a tetraploid composition ranging from 38% to 80%. Heavy mortality of putative tetraploid larvae occurred at about 7–9 days and juveniles (1, 3, and approximately 200) were harvested in three groups. Unfortunately, these juveniles were lost during a hurricane in October 2018 at the growout site of one collaborating farm before individual ploidy examination. Although no confirmed tetraploid founders were harvested, the occurrence and fecundity of triploid females were documented in detail, which should be useful for future development of tetraploid stock for oyster aquaculture.