Bacterial microbiota of eggs from cage-reared and tank-reared grouper, Epinephelus coioides

Abstract

At SEAFDEC AQD, opaque spawned grouper eggs are observed during collection in cage-reared brood stock; while opaque and multi-colored eggs are often observed in tank-reared fishes. This study aimed to investigate the occurrence of these opaque and multicolored eggs and at the same time to compare the bacterial microbiota of eggs from brood stock reared in cages, to those from fish reared in concrete tanks. Grouper eggs from brood stocks reared in cages and tanks were processed for bacterial count and identification. Results showed that total bacterial count (on MA) and presumptive Vibrio count (on TCBS) of eggs from brood stock reared in concrete tanks were lower than those from cage-reared fishes. Aeromonads (for tank-reared) and Pseudomonads (for cage-reared) were the dominant bacteria in the good eggs; while Vibrios were dominant in the bad eggs for both egg sources. Total bacterial count of the egg-incubating medium from the brood stock tanks (10⁴ cfu/ml) was lower than the total bacterial count of water from the cages (10⁷ cfu/ml). Presumptive Vibrio counts of water from the tanks (10² cfu/ml) were lower than those from the cages (10⁶ cfu/ml). The Aeromonads dominated the water from the tanks; while Vibrios dominated those from the cages. Good eggs that did not hatch, turned yellow after 3 days, and pink after 5 days.