Streptococcus agalactiae (Group B Lancefield) has emerged as a significant pathogen affecting both humans and animals, including aquatic species. Infections caused by S. agalactiae are becoming a growing concern in aquaculture and have been reported globally in various freshwater and marine fish species, particularly those inhabiting warm water environments. This has led to numerous outbreaks with high morbidity and mortality in fish. Nile tilapia (Oreochromis niloticus), a member of the Cichlid family, is one of the severely affected fish species by S. agalactiae. The current study aims to focus on S. agalactiae infection in cultured O. niloticus with reference to its transmission and sources of infection; risk factors influencing GBS infection, disease clinical signs, lesions, and pathogenesis; S. agalactiae virulence factors; and how to diagnose, treat, control, and prevent infection including vaccination and herbal extract medication.

This study investigated the ethanolic leaf extract of Brazilian pepper tree (Schinus terebinthifolius Raddi) for its metabolite composition and effects on growth performance and intestinal immune gene expression in Nile tilapia (Oreochromis niloticus). Ultra-performance liquid chromatography-electrospray ionization-mass spectrometry (UPLC-ESI-MS/MS) in positive and negative modes revealed a diverse profile of 33 peaks in each polarity, identifying key compounds such as phenolic acids (e.g., gallic acid and ferulic acid), flavonoids (e.g., myricetin-O-glucoside and quercetin 3-O-glucoside), gallotannins (e.g., glucogallin and pentagalloylglucose), and triterpenoids (e.g., masticadienoic acid). A 60-day feeding trial with four groups (control and three extract doses; 0.5%; T0.5%, 1%; T1% and 2%; T2%) demonstrated dose-dependent enhancements in growth metrics, where final body weight increased by up to 106.9 ± 3.6 g, weight gain% by 197.3 ± 3.5%, and the growth rate got more than doubled in T2% (2.4 ± 0.1), alongside improved feed conversion ratio (1.24 ± 0.01) at 30 days and condition factor (stabilized at 2.1 ± 0.0) at 60 days post-feeding. Viscero- and gastro-somatic indices declined insignificantly in most feed groups, indicating improved muscle growth. Biphasic patterns were observed in intestinal gene expression as follows: over 60 days, the IL-1β gene upregulated at low doses but returned to normal at high doses. The IL-10 gene upregulated progressively, promoting an anti-inflammatory balance. In fish fed medium and high doses (T1% and T2%), the IgM gene is upregulated, supporting humoral immunity. These outcomes, linked to the extract’s previously described antioxidants, anti-inflammatory, and antimicrobial bioactive compounds, suggest that S. terebinthifolius is a promising natural feed additive for sustainable tilapia aquaculture and warrants further validation for commercial application.

In river Nile and its branches, numerous individuals of red swamp crayfish, Procambarus clarkii, displayed melanised areas in gills. To clarify the cause of these lesions, several isolates of Fusarium spp. were recovered. The fungi were first identified morphologically on culture media. Subsequently, molecular identification was carried out based on the internal transcribed spacer (ITS) region and beta-tubulin gene (TUB2) sequences. Based on GenBank database searches, the causative agent was identified as Fusarium solani. To fulfill Koch`s postulates, an experimental infection was induced using a representative isolate (ESHA-1). The challenged crayfish showed similar lesions noticed on naturally-infected ones, and the pathogen was re-isolated from the lesions of the infected individuals. Zinc oxide nanoparticles (ZnO NPs) exhibited a significant reduction in fungal growth. To our knowledge, this is the first record of Fusarium solani infection in red swamp crayfish inhabiting the River Nile.

The present study aimed to isolate and characterize bacteriophages (phages) specific for Edwardsiella ictaluri to be used as a biological control of the infection in fish as a final goal. Twenty-six phages (PEi1 ~ PEi26), lytic to E. ictaluri were isolated from ayu Plecoglossus altivelis and its surrounding environment (water and mud) using enrichment and double agar layer methods. All phages formed clear plaques ranging in size from 0.3 to 8 mm in diameter. Transmission electron microscopy revealed that all the isolated bacteriophages belonged to the family Myoviridae. According to phage morphology, plaques size and DNA restriction patterns with EcoRI, the phages were classified into four groups (I ~ IV). E. ictaluri strains isolated from ayu (n=57) were sensitive to these phages with various degrees, resulting in twenty-five phage types of the bacterium. E. ictaluri strains isolated from catfish in the USA (type strain; JCM1680), Indonesia (n=4) or Vietnam (n=2) exhibited no or very limited susceptibility to the present phages. In addition, E. tarda, the most closely related species to E. ictaluri, as well as other fish pathogens were not susceptible to any of the phages examined.

The present study was carried out to investigate the common bacterial infections of some saltwater fishes in Red Sea at Hurghada, Egypt. One hundred and twenty fishes of different species including Hipposcarus harid, Scarus ferrugineus and Scarus niger were subjected to bacteriological investigations.The bacteria isolated from the vital organs were phenotypically identified as Vibrio logei, V. ichthyoenteri, V. fischeri, Moritella marina, Photobacterium damselae subsp. piscicida and Edwardsiella tarda, in addition to two isolates of the genus Streptococcus. Experimental challenge with the dominant isolate, V. logei, proved its pathogenicity to H. harid with 86.7% mortality rate. Histopathological investigations of experimentally infected fish disclosed prominent pathological alterations in vital organs including liver and kidney. The antibiotic sensitivity of V. logei, revealed its sensitivity to Norfloxacin, Ciprofloxacin and Ofloxacin.

Spring viremia of carp (SVC) is a contagious viral disease that causes high mortality among infected fish. The present study aimed to investigate the expression profile of tumor necrosis factor alpha (TNF-α) gene following experimental infection of Nile tilapia (Oreochromis niloticus) with SVCV. Fish was exposed to SVCV (3.2×107 TCID50/ml) by immersion for 4 hrs. Then, spleens of both infected and control fish were sampled at various time points (1 h, 12 h, 1 d, 3 d, 5 d, 7 d, 11 d, and 14 d) post-infection (pi). The expression of TNF-α gene, at these time points was assessed using reverse transcription quantitative real-time PCR (RT-qPCR). The results revealed a significant upregulation of TNF-α gene that starts from 12 hrs pi, and continued to reach its peak at the 3rd dpi recording a fold change of 2.3 and 6.1, respectively, compared to the control. Subsequently, TNF-α gene expression commenced to regress at 5th dpi until it became similar to its corresponding control at 11th and 14th dpi. To the best of our knowledge, this is the first study exploring one of the immune responses of Nile tilapia after SVCV infection.