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Vibrio harveyi , which belongs to family Vibrionaceae of class Gammaproteobacteria , includes the species V. carchariae and V. trachuri as its junior synonyms. The organism is a well-recognized and serious bacterial pathogen of marine fish and invertebrates, including penaeid shrimp, in aquaculture. Diseased fish may exhibit a range of lesions, including eye lesions/blindness, gastro-enteritis, muscle necrosis, skin ulcers, and tail rot disease. In shrimp, V. harveyi is regarded as the etiological agent of luminous vibriosis in which affected animals glow in the dark. There is a second condition of shrimp known as Bolitas negricans where the digestive tract is filled with spheres of sloughed-off tissue. It is recognized that the pathogenicity mechanisms of V. harveyi may be different in fish and penaeid shrimp. In shrimp, the pathogenicity mechanisms involved the endotoxin lipopolysaccharide, and extracellular proteases, and interaction with bacteriophages. In fish, the pathogenicity mechanisms involved extracellular hemolysin (encoded by duplicate hemolysin genes), which was identified as a phospholipase B and could inactivate fish cells by apoptosis, via the caspase activation pathway. V. harveyi may enter the so-called viable but nonculturable (VBNC) state, and resuscitation of the VBNC cells may be an important reason for vibriosis outbreaks in aquaculture. Disease control measures center on dietary supplements (including probiotics), nonspecific immunostimulants, and vaccines and to a lesser extent antibiotics and other antimicrobial compounds.

Tenacibaculosis occurs due to the marine bacterial pathogen Tenacibaculum maritimum . This ulcerative disease causes high mortalities for various marine fish species worldwide. Several external clinical signs can arise, including mouth erosion, epidermal ulcers, fin necrosis, and tail rot. Research in the last 15 years has advanced knowledge on the traits and pathogenesis mechanisms of T. maritimum . Consequently, significant progress has been made in defining the complex host-pathogen relationship. Nevertheless, tenacibaculosis pathogenesis is not yet fully understood. Continued research is urgently needed, as demonstrated by recent reports on the re-emerging nature of tenacibaculosis in salmon farms globally. Current sanitary conditions compromise the development of effective alternatives to antibiotics, in addition to hindering potential preventive measures against tenacibaculosis. The present review compiles knowledge of T. maritimum reported after the 2006 review by Avendaño-Herrera and colleagues. Essential aspects are emphasized, including antigenic and genomic characterizations and molecular diagnostic procedures. Further summarized are the epidemiological foundations of the T. maritimum population structure and elucidations as to the virulence mechanisms of pathogenic isolates, as found using biological, microbiological, and genomic techniques. This comprehensive source of reference will undoubtable serve in tenacibaculosis prevention and control within the marine fish farming industry. Lastly, knowledge gaps and valuable research areas are indicated as potential guidance for future studies.

The primary natural resource we use in our daily lives for a variety of activities is freshwater for drinking and various developmental goals. Furthermore, the pace of human population increase worldwide is rising rapidly and has a great impact on the Earth’s natural resources. Natural water quality has diminished owing to various anthropogenic activities. Water is crucial to the life cycle. On the other hand, chemical and agricultural industries pollute heavy metals. Acute and chronic diseases caused by heavy metals, such as slow metabolism and damage to the gills and epithelial layer of fish species, are divided into two categories. Pollutants can also harm liver tissues and result in ulceration as well as diseases such as fin rot, tail rot, and gill disease. The most prevalent heavy metals are As, Cr, Pb, and Hg, which are systemic toxicants that affect human health. These metals are categorized as carcinogens by the US Environmental Protection Agency and the worldwide agency for cancer research because they cause organ damage even at low exposure levels. The focus of the current study is to review various freshwater sources of heavy metal pollution.

The aquaculture sector is facing environmental issues because of rising chemical pollution of aquatic systems, which may be caused by man-made or natural causes. The combined action of these mixtures can produce an effect that is either severalfold higher or severalfold lower than the overall toxicity of the individual components. The objective of this study is to evaluate the impact of three individual toxicants: lead (Pb 0.088 mg L −1 ), mercury (Hg 0.084 mg L −1 ), and pendimethalin (PM 0.355 mg L −1 ) and their combinations on the behavior, oxidative stress, immunology, biochemistry, and histopathological changes in Nile tilapia. The results show that mortality was evident across all treatment groups and was highest in the mixture (MIX) group, at 33.4%. Some of these behavioral changes included increased mucus secretion, fin rot, and dark skin coloration of the fish, all of which were evidently exacerbated in the MIX group. The erythrocyte and hemoglobin indices presented marked reductions in the MIX and PM groups in comparison to the control group. The MIX group had higher levels of serum creatinine and urea, as well as the liver enzymes alanine aminotransferase, aspartate transaminase, and alkaline phosphatase. They also had higher levels of malondialdehyde and lower levels of total antioxidant capacity, which showed oxidative stress. The stress biomarkers, cortisol and glucose, showed greater impact on the MIX and PM groups. The neurobehavioral assessment demonstrated noticeable decreased acetylcholinesterase levels in PM and MIX-exposed groups. In the serum immunological parameters, levels of nitric oxide and lysozyme were lower, especially in the MIX and PM groups. In all experimental groups, especially the MIX group, the levels of spleen pro-inflammatory cytokine genes were higher. The histopathological examination revealed marked lesions in the gills, liver, and brains in the form of inflammation, necrosis, and circulatory alterations. Among the exposed groups, the MIX group exhibited the highest histopathological changes. Collectively, our findings demonstrated significant toxic effects of heavy metals and herbicides on Nile tilapia, revealing a synergistic impact on both physiological and histopathological responses resulting from combined exposures. The data evidently indicate the ecological hazards associated with heavy metals and herbicides in aquatic ecosystems.

Hexaflumuron (HEX) insecticide is widely used in agriculture practices to fight crop insects. The toxicological effect of HEX on Nile tilapia (Oreochromis niloticus) was investigated in this study. Two hundred and forty fish (35.50 ± 1.45 g) were divided into six groups in four replicates (40 fish/group; 10 fish/replicate) and were exposed to six distinct HEX concentrations (0, 2, 4, 6, 8, and 10 mg L−1) for 96-h. The 96-h lethal concentration 50 (96-h LC50) of HEX was calculated to be 7.19 mg L−1. The fish exhibited reduced surface and middle swimming, aggressiveness, and tail-spreading behaviors with increasing bottom swimming and resting patterns after HEX exposure. HEX exposure resulted in body bleeding and fin rot. The erythrogram (red blood cell count, hemoglobin, and packed cell volume %) was significantly reduced with increased mean corpuscular volume by HEX exposure. HEX exposure decreased the white blood cells (WBCs) and differential WBC counts. Acute HEX exposure raised 8-hydroxy-2-deoxyguanosine level while lowering brain acetylcholine esterase activity. HEX exposure caused hepato-renal dysfunction and increased stress-related parameters (glucose and cortisol). Exposure to HEX reduced the immune responses (lysozyme, nitric oxide, immunoglobulin M, and complement 3). A substantial decrease in the antioxidant variables (reduced glutathione content and catalase) with increasing the malondialdehyde was noted by HEX exposure. Moreover, histopathological changes resulted from HEX exposure in the gills, liver, kidney, and spleen. These results indicate that HEX exposure induced behavioral changes, hepato-renal dysfunction, and immune-antioxidant disruption, indicating a possible physiological disruption in O. niloticus.

In the study, Aeromonas strains (n = 12) were isolated from moribund grass carp fry reared in the cage culture unit from the Central Himalayan region of India. They were identified as Aeromonas veronii, by biochemically and 16S rRNA analysis. The experimental bath infection of grass carp fry was performed using A. veronii GCAFBLC 228, one of the 12 isolates at cell concentrations 106 and 108 CFU mL−1. The infected fry showed varied behavioural characteristics followed by tail rot, black pigmentation and hemorrhage in the body 48–96 h post infection. The post bath challenged demonstrated maximum mortality (23%) at cell concentration 108 CFU mL−1 during 10th and 12th day. Histopathology revealed hypertrophy, hyperplasia, fusion of gill lamellae, detachment and epithelial cell detachment in gill, swelling of hepatocytes, granular deposition in liver and tubular degeneration and yellow pigmented macrophage aggregates in the kidney. The in vitro assays for virulence traits recorded that A. veronii GCAFBLC 228 was β-haemolytic having strong cell surface hydrophobicity (CHS) characteristic (> 50%), precipitated after boiling, produced slime, non-suicidal and bound to crystal violet. The antibiogram showed that the strain was susceptible to ciprofloxacin (5 μg), cefotaxime (30 μg), ceftazidime (30 μg), cefoxitin (30 μg), ceftriaxone (30 μg), chloramphenicol (30 μg) and tetracycline (30 μg). Negative staining transmission electron microscopy revealed presence of the lateral flagellum-like structure and cell adherence possibly could be correlated with the pathogenicity of A. veronii GCAFBLC 228. The further investigation is warranted to study the transmission, pathogenesis and epidemiology of A. veronii GCAFBLC 228 to develop the best health management practice for cage farmed fish.

Bacterial illness causes detrimental impacts on fish health and survival and finally economic losses for the aquaculture industry. Antibiotic medication causes microbial resistance, so alternative control strategies should be applied. In this work, we investigated the probiotic-medicated diet as an alternative control approach for antibiotics in treating Vibrio cholerae infection in Nile tilapia (Oreochromis niloticus). One hundred eighty fish (50 ± 2.5 g Mean ± SD) were allocated into six groups in glass aquariums (96 L) in triplicate for 10 days. Groups 1 (G1), G2, and G 3 were intraperitoneally (IP) injected with 0.5 mL sterilized tryptic soy broth and fed on a basal diet, basal diet contained B. subtilis (BS) (1 × 10 5 CFU/ kg-1 diet), and basal diet contained trimethoprim-sulfamethoxazole (TMP-SMX) (1.5 g/kg-1 diet), respectively. Additionally, G4, G5, and G6 were IP challenged with 0.5 mL of V. cholerae (1.5 × 107 CFU) and received the same feeding regime as G 1 to 3, respectively. The results exhibited that the V. cholera-infected fish exhibited skin hemorrhage, fin rot, and the lowest survival (63.33%). Additionally, lowered immune-antioxidant biomarkers (white blood cells count, serum bactericidal activity, phagocytic activity, phagocytic index, and lysozymes) with higher lipid peroxidation marker (malondialdehyde) were consequences of V. cholerae infection. Noteworthy, fish-fed therapeutic diets fortified with BS and TMP-SMX showed a substantial amelioration in the clinical signs and survival. The BS diet significantly improved (P < 0.05) the immune-antioxidant indices of the infected fish compared to the TMP-SMX diet. The current findings supported the use of a BS-enriched diet as an eco-friendly approach for the control of V. cholerae in O. niloticus.

This study assessed fish farms, general fish health management, disease occurrences, and management practices in Tanzania’s pond and cage culture systems. Data were collected using semistructured questionnaires from operational farms across three regions (Pwani, Dar es Salaam, and Mwanza). The questionnaire survey assessed farmers’ demographic data, general pond management practices, and health management issues, including pond treatment, the use of disinfectants and antibiotics, disease and mortality, fish waste management, and net handling. The results showed that the majority (93.2%) of respondents were male, and 34.1% were aged 40–49 years. Most farmers owned ponds/tanks (69.7%), and the remaining owned cages (30.3%). Tilapia was the most farmed fish species (97.0%), followed by the polyculture of tilapia and catfish. Except for the lake, where all cage farms were located, rivers, springs, wetlands, boreholes, and municipal piped water were other sources of water. All water sources for pond‐based farms lacked pretreatment reservoirs. Most fish farms (87/131) had experienced fish diseases and mortalities. Only 20.6% of respondents reported receiving training in fish health and disease management. Most respondents knew that fish could get sick, but training in disease diagnosis was poor. The clinical signs that respondents listed included decreased feed intake, erratic movements, skin ulcers, a distended abdomen, darkened skin, white skin patches, fin rot and scale erosion, stunted growth, and protruding eyes. The survey suggests that training attendance and self‐reported diagnostic capacity were limited among farmers in the surveyed regions. Training and capacity building for farmers in disease diagnosis and management are a way forward for enhancing the sustainability and profitability of tilapia farming in Tanzania.

Tail rot disease is associated with major economic losses in the seahorse aquaculture in China. This study aimed to isolate and identify the pathogen causing tail rot disease in seahorses. Three culturable intestinal bacteria strains were isolated from Hippocampus kuda specimens with tail rot disease. Strain HL11, HL12, and HL13 were identified as Pseudoalteromonas spongiae, Bacillus subtilis and Photobacterium ganghwense based on its morphological characteristics, physiological and biochemical properties, through 16S rRNA and gyrB sequencing, respectively. Challenge experiments using these strains on healthy H. kuda and bacterial re-isolation from challenged diseased seahorses showed that the bacteria strain named HL11 induced identical pathological symptoms, indicating that it is the causative pathogen of the disease. Antibiotic-resistance tests against of 32 antibiotics revealed that HL11 was highly sensitive to 13 kinds, while exhibited intermediate susceptibility to 6, and resistance to 13 kinds. Antibacterial tests of the bioactive agents showed that HL11 was susceptible to five kinds, including tea polyphenols, lactic acid, gallic acid, allicin, and polylysine; however, it was not susceptible to the other 13 kinds of bioactive agents. The results demonstrate the potential of using bioactive agents to replace antibiotics to generate an environmentally friendly mode of culturing seahorses.

Cage aquaculture in Lake Victoria has expanded rapidly, yet disease outbreaks remain a major constraint to productivity and farmer livelihoods. This study assesses the economic impact of bacterial disease outbreaks on cage fish farms in Tanzania's Lake Victoria Basin, focusing on Mwanza, Simiyu and Mara regions. Using a multi‐stage cluster sampling method, 84 cage fish farmers were surveyed across six districts. Our findings reveal that bacterial diseases, particularly fin and tail rot, were most prevalent, with medium‐level outbreaks (affecting 11%–30% of fish) reported in over half of the farms. The average mortality rate was 15.92%, resulting in significant economic losses ranging from1800 to 19,093 per production cycle. Poor biosecurity, handling practices and water quality were key contributors to disease spread. Profitability indicators such as gross margin, net income and profit ratio declined sharply with increasing mortality. Farms with lower mortality rates achieved better financial outcomes, while those with higher mortality faced reduced output and rising costs. The study highlights the urgent need for improved disease management, biosecurity training and support services to enhance the sustainability and profitability of cage fish farming in the region.