Summer Mortality Syndrome Affecting Cultured European Seabass at Kafrelsheikh Province, Egypt

Abstract

The present work aimed to investigate the causes of summer mortality syndrome affecting cultured European seabass (Dicentrarchus labrax) by examining physiochemical farm water characteristics, isolation, and identification of recovered bacterial pathogens from diseased fish studying the effect of water temperature on stress biomarkers and disease severity. Studied water parameters were normal except ammonia and dissolved oxygen was higher and lower than the standard value. Sixty-two bacterial isolates were recovered from moribund fish and identified as 31 Vibrio fluvialis, 23 Pseudomonas aeruginosa and 8 Staphylococcus aureus isolates. The calculated LD50 of V. fluvialis, P. aeruginosa and S. aureus for D. labrax fingerlings were 4.67 × 107, 2.37 × 106 and 1.38 × 107, respectively. There was a direct correlation between water temperature and mortality rate of fish challenged with V. fluvialis as the mortality rate was 44.44, 50, 66.66, and 83.33% for fish maintained at 27, 30, 33, and 36°C. Plasma cortisol, superoxide dismutase, catalase and malondialdehyde significantly increased when the water temperature exceeded 30°C. The experimentally infected fish showed similar clinical signs and postmortem lesions of naturally diseased fish with no boundary between different pathogens. Antibiogram test indicated that florfenicol was the most effective antibiotic against all the recovered bacterial isolates while all isolates resisted sulfamethoxazole-trimethoprim. Massive degenerative changes observed in the hepatopancreas, posterior kidney and gill tissues of experimentally infected fish.

Genetic characterization and antimicrobial profiling of bacterial isolates collected from Nile tilapia (Oreochromis niloticus) affected by summer mortality syndrome

“…In recent years, Egyptian tilapia farms have faced unusual mortality episodes, particularly during the summer season with high mortality rate and general signs of septicemia, which known as Summer Mortality Syndrome “SMS”. The phenomenon was firstly reported by Fathi et al, 2017 in tilapia farms, however, SMS has been used recently to describe unusual mortalities in marine fish, Cultured European Seabass (Ali et al, 2021). The same study has identified some bacterial pathogens ( Vibrio fluvialis , Pseudomonas aeruginosa , and Staphylococcus aureus ) from the affected fish.…”

The role of Aeromonas genotyping in virulence for Dicentrarchus labrax

“…Vitek 2 Compact system (bioMérieux, France) was used for bacterial isolate identification using the Gram‐negative card according to the method described by Ali, El‐Nokrashy, et al. (2021). The biochemical profile of each isolate was determined at different time points and then automatically matched with the system database.…”

“…Cortisol was extracted as described by Ali, El‐Nokrashy, et al. (2021); plasma cortisol was assayed by measuring the absorbance at 415 nm in a microplate reader model AO, Azure Biosystems, USA, using the Cayman cortisol determination kit, USA.…”

“…Cortisol is the most abundant corticosteroid in fishes; cortisol is secreted in response to many stress conditions and diseases (Ali, El‐Nokrashy, et al., 2021). Cortisol plays a regulatory role in the fish immune system; it downregulates the inflammatory response and reduces antibody production and humoral immune response.…”

Virulence associated genes profiling of Streptococcus iniae isolated from diseased Nile tilapia Oreochromis niloticus

“…The diseased fish show the general signs of septicemia (Ali et al, 2018). Ali et al (2021b) reported that thermal stress is the main predisposing factor for the summer mortality syndrome associated with disease outbreaks affecting cultured fish, stressed fish became immune-compromised and highly susceptible to bacterial diseases. resistance (Baiano and Barnes, 2009).…”