HYBRIDIZATION OF Crassostrea belcheri ♀ × C. iredalei ♂ IMPROVED THE SURVIVAL AND GROWTH UNDER HATCHERY CONDITIONS OVER PURE STRAINS

Fariborz Ehteshamei *, Nicholas  , Annie Christianus ,  Mehdi Ebrahimi,
Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
ehteshami@upm.edu.my  

Crassostrea belcheri and C. iredalei are commerically important oyster species for food throughout Southeast Asia, however their spat supply can be unpredictable for aquaculture. To potentially improve larval productivity, hybridization was conducted with C. belcheri females and C. iredalei males (CBCI) and C. iredalei females and C. belcheri males (CICB).  The fertilization rate, larval survival and development at different larval stages (D-stage, umbo, eyed-larvae and pediveliger) and spat after 100 days of these hybrids were compared with pure larval strains of C. belcheri (CBCB) and C. iridalei (CICI), which was confirmed from genetic analysis.  Three male and female oysters from each treatment were stripped, eggs fertilized and the larvae stocked at 4/ml.  All larvae were fed at the same rate with microalgae.  Results showed that the fertilization rate of CICI and CBCB was >80%, which was significanlty higher compared to the  hybrids, with CICB significanlty lower than all treatments at 30%.  Survial at each stage was similar, however at the pediveliger stage, survival was significantly higher for CBCI compared to the CICB cross.  For growth, CBCB was significantly higher than the CICI at the D-stage, but no significant differences were detected among the treatments up to the pediveliger stage (Table 1).  On day 30 after becoming spat, the CICB cross were significantly larger than all other treatments, however after 100 days of culture, the CBCI treatment became significantly bigger than CICI (Table 2).  Results indicate that the larger size of oyster spat is maternally inherited from C. belcheri.  The fatty acid composition of the spat revealed CBCI had higher C20:5n-3 than others while C22:6n-3 was higher for CICB.  Total n-3 and n-6 was higher and lower for CBCI, respectively.

To the best of our knowlegde this is the first report on the hybiridization of C. belcheri and C. iridalei.  The higher survival of CBCI during the pediveliger stage along with larger size appears promising to improve larval productivity.