Growth performance and disease resistance against Vibrio vulnificus infection of novel hybrid grouper ( Epinephelus lanceolatus x Epinephelus fuscoguttatus)

Groupers are economically important for aquaculture in Thailand. A novel hybrid grouper (Epinephelus lanceolatus x Epinephelus fuscoguttatus) has been successful cross-bred; therefore, the present work aimed to assess the hybrid's traits. The growth performance, strength and tolerance to a pathogenic bacterial infection of this hybrid were compared with its parent species, tiger grouper and giant grouper. The results of all measured growth parameters indicated that the hybrid strain grew fastest followed by giant and tiger grouper respectively. The expressions of the growth-related genes, insulin-like growth factor (IGF) I and II, were also analysed in fish muscle and liver which are the main target organs in fish growth regulation. Among tested species, similar expression patterns of IGF-I and IGF-II were detected in both organs. The levels of these genes in liver and muscle of hybrid and giant grouper were higher than those of tiger grouper comparable with the growth manner. After challenge with Vibrio vulnificus, the immunological parameters, clearance time of Vibrio in haemolymph and survival was measured to verify the fish immunity. Leucocyte number, lysozyme activity and the ability to eliminate the pathogen were very high in hybrid and giant grouper while these parameters were lower in tiger grouper. Correspondingly, the mortality rate of tiger grouper was higher than others and % survival at the end of observation time (15 days post challenge) was lowest in infected tiger grouper. Altogether, the results suggested that the hybrid grouper has desirable traits that will improve cultured grouper.