Low water temperature, dissolved oxygen, and pH outside of the 6-9 range can cause stress which can result in disease. Rough handling of fish during transport to the farm or sorting for market, and overcrowding, can remove skin and scales from the fish which then become more susceptible to infection. Vibriosis is a bacterial infection which has caused the death of snapper farmed in sea-cages. Vibriosis typically appears as white, circular lesions on the sides of fish. Infected fish are dark in colour, sluggish, do not feed well and can die in large numbers.
Fingerlings are usually more susceptible to vibriosis than advanced fish.
Outbreaks of vibriosis can be controlled by antibiotics, such as oxytetracycline, added to the pellet diet. Other options for prevention may include stocking fingerlings well before the onset of winter and avoiding handling the fish during winter. The gill fluke parasite, Bivagina pagrosomi , has also caused disease in farmed snapper. The adult flukes attach to the gills and skin and when present in large numbers can cause severe blood loss. Infected fish are dark and sluggish and do not feed well.