Effects of hybridization between Nile tilapia (Oreochromis niloticus) and blue tilapia (Oreochromis aureus) on immune response to Aeromonas hydrophila

Effects of hybridization between Nile tilapia (Oreochromis niloticus)
and blue tilapia (Oreochromis aureus) on immune response to
Aeromonas hydrophila
Waleed N. El-Hawarry* and Talat T. Saad**
*Department of Animal Husbandry and Animal Wealth Development, Faculty of Veterinary Medicine, Alexandria
University, Egypt.
**Poultry and Fish Disease Department, Faculty of Veterinary Medicine, Alexandria University, Egypt.
E-mail: [email protected]
Received 1st November 2011, Accepted 30th December 2011
Abstract
Resistance to Aeromonas hydrophila infections (mostly occur during environmental changes, stressors, change
in the temperature, in contaminated environments), in three genotypes of tilapias, Nile tilapia (Oreochromis
niloticus), blue tilapia (Oreochromis aureus) (males and females) as well as their crossbred hybrid (♂O. aureus x
♀O. niloticus) was studied. Based on comparison of non-specific immunity; the crossbred hybrid (♂O. aureus x
♀O. niloticus) showed the highest percentage of phagocytic activity and phagocytic index in comparison to
purebred genotypes. Meanwhile, the purebred ♀O. aureus showed the lowest levels for the former non-specific
immune parameters at the base line level and post vaccination with the A. hydrophila vaccine. Similarly, the
crossbred hybrid (♂O. aureus x ♀O. niloticus) showed the highest antibody titers against A. hydrophila pathogen
following booster vaccination and challenge infection by the virulent A. hydrophila. Meanwhile, the vaccinated
mortality percentages and the relative level of protection (RLP %) were the lowest and the highest respectively for
the crossbred hybrid (♂O. aureus x ♀O. niloticus). These results suggest that there is a potential for genetic
improvement of disease resistance in aquatic animals since a specific variation exists in immunity against a specific
pathogen and consequently, hybrid may be used to create a broad genetic base for future selection programs.
Keywords: Purebred, Oreochromis niloticus, Oreochromis aureus, inter-specific hybrid tilapia, immune response,
Aeromonas hydrophila.