This study reports the optimization of a cost-effective one-step PCR assay for the detection of White Spot Syndrome Virus (WSSV) in wild shrimp populations, providing an accessible alternative to expensive commercial nested PCR kits in Mozambique. Primer sets targeting VP19, VP24, VP26 and VP28 were evaluated, with the VP28_2 primer set demonstrating the highest sensitivity and no cross-reactivity with Infectious Hypodermal and Haematopoietic Necrosis Virus (IHHNV) or Decapod Iridescent Virus 1 (DIV1). Cost analysis showed that the optimized assay is approximately three times less expensive than commercial nested PCR (USD 5.57 vs. USD 15.75 per reaction). The assay was applied to 300 wild shrimp specimens (Penaeus indicus and Penaeus monodon) collected during a cross-sectional survey conducted in the rainy season (October-November 2022) at 15 landing sites across six provinces. WSSV was detected in 60.7% of samples, with significant regional variation: 78.0% in the South, 58.0% in the Centre and 48.1% in the North. Although the findings indicate widespread WSSV occurrence in wild shrimp populations, the cross-sectional design, single-season sampling and sample size limit inference on temporal trends. Nevertheless, the optimized assay provides a practical and affordable tool for routine WSSV surveillance under existing resource constraints.

Introduction: Antibiotics are commonly used to treat infections and promote fish welfare in Aquaculture. Reports suggest that the use of antibiotics in fish farming often breaches established protocols, frequently accumulating in fish muscles and sediments. These residues are known to be detrimental to the fish, altering antioxidant activity and immune responses, and posing environmental risks. In this study, we aimed to investigate the presence, types and quantify, quantify the levels of antibiotic and residues in Nila tilapia (Oreochromis niloticus) fish muscles and sediment samples, and evaluate the associated health risks to humans and the aquatic ecosystem in Stratum II of Lake Volta, Ghana. Methodology: Muscles of table-sized fish and sediment samples were collected from cage aquaculture farms along the Stratum II of the Lake Volta, Ghana, and analysed using Liquid Chromatography with tandem mass spectrometry (LC-MS-MS) for the presence of antibiotic residues. Variations in residual antibiotic concentrations and basic sediment properties throughout the various strata of the Lake Volta were examined using analysis of variance (ANOVA) with a general linear model (GLM). A post-hoc test for multiple comparisons with a significance level of p < 0.05 was performed using Tukey's HSD technique. Potential antibiotic sources were examined using principal component analysis (PCA). Possible risks to human health and the environment were estimated using risk quotients described in the European Technical Guidance Document on Risk Assessment. Results: Four antibiotics, namely ciprofloxacin, tetracycline, chloramphenicol, and azithromycin, were identified in both fish muscle and sediments, with Azithromycin, tetracycline, and ciprofloxacin residues being the most frequently detected antibiotics. Except ciprofloxacin which showed higher concentration midstream, the rest showed higher concentrations of the detected antibiotic residues from downstream sites. Risk analysis of antibiotic residues in fish muscle tissues and sediments revealed risk quotients that ranged from 0.0024-0.0382 for humans and from 0.0200-0.5713 for the aquatic ecosystem in the Lake. Discussion and conclusion: The detection of antibiotic residues in both fish muscle and sediment from aquaculture farms along Lake Volta suggests evidence of antibiotic use or contamination in fish farming in the Lake Volta. Though current antibiotic levels may not pose immediate risks, their accumulation, particularly Chloramphenicol, which has been banned for use in aquaculture, could contribute to antimicrobial resistance making it difficult for future treatment of human infection as well as compromising the food quality and safety. Antibiotic residues in fish and sediments from Lake Volta aquaculture signal contamination risks and a potential threat to future infection treatment

Background Environmental contaminants pose significant threats to aquatic ecosystems and human health. While most studies have focused on the occurrence, levels and risk assessments of the environmental contaminants within aquatic ecosystems, there is limited and poorly documented information regarding fish farmers’ and fishermen’s knowledge and practices that may contribute to aquatic contamination. To address this gap, the present study investigated the knowledge and practices of fish farmers and fishermen concerning environmental contaminants, with particular emphasis on their sources and potential implication in fish and human health. Methods A cross-sectional study was conducted among 171 fish farmers and fishermen across 6 districts in Malawi: Chikwawa, Karonga, Machinga, Mangochi, Mchinji and Zomba, covering all 3 regions of the country. A semi-structured questionnaire and personal observation were used to collect data and statistical software STATA was used for data analysis. Results The study revealed that the majority of both the fish farmers and fishermen had only attained primary education (81.8%) and (86.1%), respectively with mean knowledge scores of (55.3%) for fish farmers and (40.3%) for fishermen on environmental contaminants. The findings also revealed a mean practice score of (31.7%) for fish farmers with extensive use of pesticides in crops that were near water bodies and the use of animal manure for pond fertilization. About (44.4%) of fishermen had insufficient knowledge on the risks of the environmental contaminants in fish. Conclusion The findings highlight the need for behavior change awareness campaigns and extension services focusing on the sources and potential health risks of the environmental contaminants in fish and humans. This study provides background information for further research on the sources and occurrence of environmental contaminants in aquatic ecosystem.

Since 2020, recurrent mortalities have been reported in grow-out farms in the Ruvu River basin in Tanzania’s Pwani region. This study investigated bacterial pathogens associated with these outbreaks. A cross-sectional survey was conducted between March 2022 and November 2023 in four affected tilapia farms. A total of 60 moribund fish were sampled. Clinical examination revealed skin ulcers, hemorrhages, fin erosion, abdominal distension, and darkened skin. Postmortem changes showed pale livers, enlarged spleens, and swollen gallbladders. Bacteria from skin lesions, kidneys, liver, and intestines were identified using selective media, morphology on agar, biochemical tests, and 16S rRNA gene sequencing, revealing six genera: Pseudomonas, Aeromonas, Bacillus, Staphylococcus, Enterobacter, and Micrococcus. Among these, Pseudomonas aeruginosa was the most frequently isolated from all farms and was strongly associated with the observed disease outbreaks. Phylogenetic analysis of P. aeruginosa further demonstrated close genetic relatedness among isolates obtained from different farms. The findings identify P. aeruginosa as the most frequently isolated bacterial pathogen associated with disease outbreaks in affected farmed tilapia within the Ruvu River basin and highlight the importance of improved biosecurity, stocking management, and aquatic animal health surveillance in Tanzania.

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.

The use and misuse of antibiotics for treating animal and human infections are a key driver of the emergence of resistant bacterial strains at the human-animal-environment interface. This inappropriate use threatens ecological balance and poses a significant risk to human health. The lack of relevant knowledge of the right attitudes and practices regarding antimicrobial stewardship among fish farmers, antibiotic drug retailers, and government agencies has significantly exacerbated this serious environmental and public health issue. To enhance understanding and improve communication for the implementation of sound antimicrobial stewardship in the fish farming industry in Ghana, this study aimed to assess the knowledge, attitude, and practices of key stakeholders regarding the use of antibiotics in cage aquaculture on Volta Lake in Ghana. We conducted a qualitative field survey involving interviews, key informant discussions, and observations. The participants were veterinary drug retailers and government officials from the fisheries, aquaculture, and veterinary sectors to gather insights about their knowledge, attitudes, and practices on antibiotics use in aquaculture. The study covered 40 respondents, comprising 18 veterinary drug retailers, 12 general pharmaceutical shop operators, five Fisheries Commission officials, and five government-trained veterinary personnel operating along the stratum II of the Volta Lake of Ghana. All quantitative and qualitative data were analysed using STATA and thematic analysis. The survey revealed that drug retailers possess limited knowledge, expertise, and education on the use of antibiotics in fish farming. It was found that drug sellers occasionally recommend treatment regimens to fish farmers based on observable symptoms associated with specific diseases. The results further revealed a lack of regulation in selling veterinary drugs to farmers. Government officials, on their part, strive to create awareness and educate farmers on the selection and appropriate use of antibiotics through routine quarterly inspections, thereby promoting best practices for cultivating healthy fish. Despite this, the results indicate insufficient coordination between government officials, drug retailers, and fish farmers regarding the usage of antibiotics in aquaculture on Lake Volta. Regular joint training programs are encouraged to improve and enhance knowledge, attitudes, and practices among government officials, veterinary drug retailers, and fish farmers. In addition, monitoring the activities of drug sellers and users, as well as fostering effective communication among all stakeholders, will significantly aid in reducing antibiotic use, misuse, and abuse in aquaculture. Under the One Health framework, efforts to integrate veterinary drug retailers, farmers, and other stakeholders of concern in antibiotic governance are required to address the increasing burden of antibiotic misuse and abuse in aquaculture in Ghana and the world.

Background: Antibiotic residue in food products and the resulting antibiotic-resistant bacteria represent a significant global public health threat. The misuse of antibiotics is a primary contributor to this issue. This study investigated the knowledge, attitudes, and practices (KAP) regarding antibiotic use among cage fish farmers on Ghana’s Volta Lake. Method: We conducted a cross-sectional survey with 91 cage fish farmers across three scales: small, medium, and large. A semi-structured questionnaire complemented by personal observations provided comprehensive data. We used several statistical methods for analysis: Pearson Chi-Square and Spearman correlation tests to examine relationships and trends among variables, logistic regression to analyze variable interactions, and Cronbach’s alpha to check internal consistency. Additionally, Kendall’s coefficient was used to rank challenges, utilizing STATA and SPSS for these calculations. Results: The survey revealed that 58.55% of cage fish farmers earn an average of 10,000 USD annually, with 35.16% having over 16 years of experience. From the survey, all sampled populations admitted to antibiotic applications in their farming operation. Knowledge of antibiotic types was mainly influenced by peers (46.15%), with tetracycline being the most recognized and used. There was a significant reliance on the empirical use of antibiotics, with 52.75% of farmers using them based on personal experience and 40.66% without a prescription. When initial treatments failed, 41.76% of the farmers would change or combine drugs. Older farmers (over 51 years) and those with tertiary education demonstrated significantly better KAP scores regarding antibiotic use. Strong correlations were also found among knowledge, attitudes, and practices in antibiotic usage. Conclusions: The findings indicate a need for improved education on antibiotic use among fish farmers to reduce misuse and enhance awareness of the potential consequences. This study provides foundational data for designing interventions to address these issues in the context of cage fish farming on Volta Lake.

The current study was carried out to investigate a wide variety of persistent organic pollutants (POPs) in wild and farmed tilapia (Oreochromis niloticus) in Lake Kariba, Zambia, and assess levels of POPs in relation to Environmental Quality Standards (EQSs). Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyls (PBDEs), and perfluoroalkyl substances (PFASs) were determined in liver samples of tilapia. PFASs compounds PFOS, PFDA and PFNA were only detected in wild fish, with the highest median PFOS levels in site 1 (0.66 ng/g ww). Concentrations of POPs were in general highest in wild tilapia. The highest median ∑DDTs (93 and 81 ng/g lw) were found in wild tilapia from sites 1 and 2, respectively 165 km and 100 km west of the fish farms. Lower DDE/DDT ratios in sites 1 and 3 may indicate relatively recent exposure to DDT. The highest median of ∑17PCBs (3.2 ng/g lw) and ∑10PBDEs (8.1 ng/g lw) were found in wild tilapia from sites 1 and 2, respectively. The dominating PCB congeners were PCB-118, -138, -153 and -180 and for PBDEs, BDE-47, -154, and -209. In 78% of wild fish and 8% of farmed fish ∑6PBDE concentrations were above EQSbiota limits set by the EU. This warrants further studies.

The current study was carried out to determine occurrence and levels of persistent organic pollutants (POPs) in wild and farmed tilapia (Oreochromis niloticus) in Lake Kariba, Zambia, and possible implications for fish health. Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyls (PBDEs), hexabromocyclododecane (HBCDD) and perfluoroalkyl substances (PFASs) were determined in liver samples of tilapia. Concentrations of POPs in wild tilapia were in general higher than in farmed tilapia, however, concentrations of DDTs and PCBs in wild tilapia foraging near the fish farms were more in the range of the farmed fish. The highest median ∑DDTs (93 and 81 ng/g lw) were found in wild tilapia from sites 1 and 2, respectively 165 km and 100 km west of the farms. DDE/DDT ratios seem to indicate recent exposure to DDT. The highest median of ∑ 17 PCBs (3.2 ng/g lw) and ∑ 10 PBDEs (8.1 ng/g lw) were found in wild tilapia from site 1 and 2, respectively. The dominating PCB congeners were PCB-118, -138, -153 and -180 and for PBDEs, BDE-47, -154, and -209. Of PFASs, only PFOS, PFDA and PFNA were detected in wild fish with highest median PFOS levels in site 1 (0.66 ng/g ww). The PCB and BDE concentrations in wild and farmed fish were above EQS biota limits set by the EU. This may suggest a risk to the fish species and threaten biodiversity.

Tilapia lake virus (TiLV) is an emerging viral pathogen of tilapiines worldwide in wild and farmed tilapia. TiLV is an orthomyxo-like, negative sense segmented RNA virus, belonging to genus Tilapinevirus, family Amnoonviridae. Here we developed a quantitative real-time PCR (qRT-PCR) assay testing primer sets targeting the 10 segments of TiLV. Sensitivity, specificity, efficiency and reproducibility of these assays were examined. Detection sensitivity was equivalent to 2 TCID50/ml when tested on supernatants from cell culture-grown TiLV. Specificity tests showed that all primer sets amplified their respective TiLV segments, and standard curves showed linear correlation of R2 > 0.998 and amplification efficiencies between 93 % and 98 %. Intra- and inter-assay coefficients of variation (CV %) were in the range of 0.0 %- 2.6 % and 0.0 %- 5.9 %, respectively. Sensitivity tests showed that primer sets targeting segments 1, 2, 3 and 4 had the highest detection sensitivities (100.301 TCID50/ml). The qRT-PCR used for detection of viral genome in TiLV infected organs gave virus titers equivalent to 3.80 log10, 3.94 log10 and 3.52 log10 TCID50/ml for brain, kidney and liver tissues, respectively as calculated on the basis of Ct values. These findings suggest that primer optimization for qPCR should not only focus on attaining high amplification efficiency but also sensitivity comparison of primer sets targeting different viral segments in order to develop a method with the highest sensitivity.

The aim of this study was to assess the levels of heavy metals in both wild and farmed tilapia on Lake Kariba in Zambia and to evaluate the impact of intensive fish farming on wild tilapia. Three sites for wild fish (2 distant and 1 proximal to fish farms) and two fish farms were selected. One hundred fish (52 from distant sites; 20 near fish farms; 28 farmed fish) were sampled and muscle tissues excised for analysis of heavy metals (Mg, Fe, Zn, Al, Cu, Se, Co, Mo, As, Cr, V, Ni, Hg, Pb, Li, Cd, and Ag) by acid (HNO3) digestion and ICP-MS. All metals were found to be below the maximum limits (MLs) set by WHO/EU. Essential metals were higher in farmed tilapia, whereas non-essential metals were higher in wild tilapia. Significantly higher levels of essential metals were found in wild fish near the fish farms than those distant from the farms. Estimated weekly intake (EWI) for all metals were less than the provisional tolerable weekly intakes (PTWI). Target hazard quotients (THQ) and Hazard Indices (HI) were <1, indicating no health risks from a lifetime of fish consumption. Selenium Health Benefit Value (HBVSe) was positive for all locations, indicating protective effects of selenium against mercury in fish. Total cancer risk (CR) due to As, Cr, Cd, Ni and Pb was less than 1 x 10(-4), indicating less than 1 in 10,000 carcinogenic risk from a lifetime consumption of tilapia from Lake Kariba. Hg levels (0.021 mg/kg) in wild tilapia at site 1 were higher than the Environmental quality standard (EQS = 0.020 mg/kg) set by EU, indicating possible risk of adverse effects to fish. Except for Hg, levels of metals in fish were safe for human consumption and had no adverse effects on fish.

Objectives Aeromonads cause severe diseases in farmed aquatic organisms. Herein, we examined 28 isolates causing disease in farmed aquatic organisms from India (n = 24) and Taiwan (n = 4) to gain insight of their genotypic and phenotypic properties. Results API 20NE biochemical phenotyping showed ≥ 90% similarity classifying all isolates as Aeromonas hydrophila . 16S rRNA genotyping showed ≥ 98% homology among all isolates with A. sobria (NR119044.1ATCC), A . veronii (MK990549.1), A. caviae (NR029252.1) and A. hydrophila (MG984625.1ATCC) and other reference strains. In contrast, gyrB showed a higher intraspecies diversity (≥ 96%) than 16S rRNA delineating the 28 isolates into three groups. Group-I consisted of seven Indian isolates clustered with A. sobria (MK484163.1ATCC), group-II comprised of five Indian and two Taiwanese isolates clustered with A. veronii AF417626.1ATCC while group-III had 11 Indian and three Taiwanese isolates grouped with A. hydrophila (AY987520.1 and DQ519366.1) reference strains. None of our isolates clustered with A. caviae (AJ868400.1ATCC) reference strain. These findings suggest that A. sobria , A. veronii and A. hydrophila could be the etiological agents of diseases observed in farmed fish and soft-shelled turtles ( Pelodiscus sinensis ) examined in this study. Overall, our findings accentuate the importance of combining phenotyping with genotyping for correct taxonomic classification of Aeromonas spp. in Aquaculture.

In this study, fish farmers’ management practices, occurrence, and knowledge of fish diseases in Nyeri County, Kenya, were evaluated. Fish farming management practices for small-scale farmers in Kenya have numerous challenges which have led to disease occurrence and reduced production. Moreover, the impact and association of these challenges to farmers’ knowledge of fish diseases and their burden has not been fully studied. A semistructured questionnaire was used to capture farmers’ biodata, fish species farmed, and farmers’ management practices such as handling of nets, pond fertilization, and disposal of fish waste. Farmers’ knowledge of fish diseases was based on their ability to identify independent and dependent variable indicators. Independent variables included clinical signs, decreased feeding, bulging eyes, floating on water, abdominal swelling, bulging eyes, abnormal skin color, reduced growth, and abnormal swimming with fish death as were the dependent variable. A total of 208 farmers were interviewed and included those of tilapia (134), mixed tilapia and catfish (40), catfish (22), rainbow trout, and five dams under cooperative management. Tilapia was the most kept fish species (66.8%) followed by polyculture of tilapia and catfish (20%) and rainbow trout (2%). Most respondents were male (78.5%) over 51 years of age (50%). Fifty percent of the respondents had secondary school education. There was a significant association between deaths and sharing of nets in Kieni East subcounty ( p = 0.0049 , chi-square), while on-farm fish waste disposing appeared to cause higher deaths compared to burning of the waste although not statistically significant ( p = 0.13 ). Few respondents observed decreased feed uptake (<20%) and poor growth. Fifty-seven percent of farmers reported mortalities. Fish poor growth, floating in water, and management practices in subcounties had significant effect on fish deaths. The farmers had knowledge of signs of diseased fish, but there was paucity of knowing the specific causes of disease. Farmers need to be empowered on best aquaculture husbandry to avoid disease transmission and specific fish disease signs to enhance proper reporting of disease for subsequent mitigation measures.

Aquaculture is the fastest food-producing sector in the world, accounting for one-third of global food production. As is the case with all intensive farming systems, increase in infectious diseases has adversely impacted the growth of marine fish farming worldwide. Viral diseases cause high economic losses in marine aquaculture. We provide an overview of the major challenges limiting the control and prevention of viral diseases in marine fish farming, as well as highlight potential solutions. The major challenges include increase in the number of emerging viral diseases, wild reservoirs, migratory species, anthropogenic activities, limitations in diagnostic tools and expertise, transportation of virus contaminated ballast water, and international trade. The proposed solutions to these problems include developing biosecurity policies at global and national levels, implementation of biosecurity measures, vaccine development, use of antiviral drugs and probiotics to combat viral infections, selective breeding of disease-resistant fish, use of improved diagnostic tools, disease surveillance, as well as promoting the use of good husbandry and management practices. A multifaceted approach combining several control strategies would provide more effective long-lasting solutions to reduction in viral infections in marine aquaculture than using a single disease control approach like vaccination alone.

The pathogenesis of Lactococcus garvieae (L. garvieae) was assessed in Nile tilapia (Oreochromis niloticus) following administration by two different routes of infection (intraperitoneal versus immersion), using 180 fish divided into three groups. The first group of fish was injected intraperitoneally (IP) with 3 × 105 colony-forming units (cfu) of L. garvieae; the second group was infected by immersion (IMM) into water containing 9.6 × 105  cfu/ml L. garvieae, and in group 3 (Control), the fish were injected IP with sterile normal saline. Mortalities were recorded daily, and on 3, 5, 7, and 13 days post-infection (dpi), liver, kidney, spleen, brain and eyes were sampled. The level of infection between groups was assessed by number of mortalities that occurred, pathology/histopathology of internal organs, bacterial re-isolation and presence of bacteria in situ determined using immunohistochemistry. A significant difference (p < .0001) was observed between L. garvieae re-isolation from tilapia following administration by IP injection and IMM. Similarly, more clinical signs and mortalities (p < .001) were observed in the IP group compared to the IMM group where no mortalities were observed. These findings suggest that L. garvieae has a low invasive potential in Nile tilapia with intact skin/external barriers and highlights the importance of maintaining fish without cuts or abrasions under field conditions.

The autovaccine was produced in-house using a bacterial isolate from a diseased fish from the target farm. Three groups of 150 fish each were injected with either 1) an oil-adjuvanted, inactivated whole cell autovaccine, 2) adjuvant only or 3) PBS (negative control). Approximately 660 degree days post vaccination, the fish were challenged with 9x105 cfu bacteria/fish by intraperitoneal injection and monitored for a further 28 days. Protection against infections was measured by lack of/reduced bacterial loads both by bacterial re-isolation and immunohistochemistry as well as absence of clinical signs/pathology. Significantly less L. garvieae (p<0.03) was re-isolated from either the adjuvant only or control groups compared to the vaccinated group. Furthermore, a significantly high amount (p<0.001) of anti-L. garvieae specific antibodies were observed in the vaccinated group compared to the adjuvant only or control groups at time of challenge. This coincided with protection against infection measured by absence/reduced L. garvieae re-isolation from internal organs, reduced clinical signs and lack of pathology in this group. In the adjuvant only and control groups, bacteria were re-isolated from the kidney, liver, spleen, brain and eyes during the first 14 days. The findings suggest that oil-based vaccines can protect tilapia against L. garvieae infection through an antibody mediated response.

This study aimed to assess antimicrobial susceptibility of members of the family Flavobacteriaceae isolated from Nile tilapia (Oreochromis niloticus). Antimicrobial susceptibility of 67 Flavobacteriaceae isolates originating mainly from ponds and Lake Victoria against 19 antimicrobial agents was determined by the broth micro dilution method. Overall, most isolates were susceptible to enrofloxacin (97%; MIC90 2 μg/ml) followed by novobiocin (85%, MIC90, 4 μg/ml) and the aminoglycoside streptomycin (85%; MIC90, 128 μg/ml). Some isolates were also susceptible towards trimethoprim/sulfamethoxazole (77.6%), neomycin and florfenicol both at 62.7%. Susceptibility levels were low for tylosin tartrate (32.8%), clindamycin and sulphathiazole both at (23.9%), ceftiofur (6%), spectinomycin (6%) and tetracyclines/oxtetracyclines (4.5%). In contrast, β-Lactams (amoxicillin, penicillin), gentamycin and erythromycin exhibited very poor activity against Flavobacteriaceae isolates. The extent of antimicrobial susceptibility did not vary significantly among isolates from farmed and wild fish isolates (P > 0.01). The highest Multiple Antimicrobial Resistance (MAR) index was observed in Chryseobacterium indologenes (0.89) and the lowest in Chaetoderma indicum isolates (0.32). Our results indicate that most of Flavobacteriaceae isolates are multidrug resistance, and this may be associated with intrinsic resistance mechanisms to a broad range of antimicrobial agents. However, the need remains to carryout in-depth study to understand better the underlying genetic mechanisms given that the magnitude and trend for susceptibility was comparable between isolates from aquaculture and fisheries. The findings from this study give us insight into appropriate choice of antimicrobial agents for effective treatment of infections caused by these isolates. Key words: Aquaculture, Fisheries, Intrinsic resistance, minimum inhibitory concentrations, ponds, Lake Victoria.

Tilapia lake virus (TiLV) causes high mortality and high economic losses in tilapines. We describe an experimental challenge study focusing on early post challenge innate immune responses. Nile tilapia ( Oreochromis niloticus ) were infected with 10 5 TCID 50 /mL TiLV intraperitoneally, followed by virus quantification, histopathology and gene expression analysis in target (brain/liver) and lymphoid (spleen/headkidney) organs at 3, 7, 12, 17, and 34 days post challenge (dpc). Onset of mortality was from 21 dpc, and cumulative mortality was 38.5% by 34 dpc. Liver and kidney histopathology developed over the period 3–17 dpc, characterized by anisocytosis, anisokaryocytosis, and formation of multinucleated hepatocytes. Viral loads were highest at early time (3 dpc) in liver, spleen and kidney, declining towards 34 dpc. In brain, viral titer peaked 17 dpc. Innate sensors, TLRs 3/7 were inversely correlated with virus titer in brain and headkidney, and IFN-ß and Mx showed a similar pattern. All organs showed increased mRNA IgM expression over the course of infection. Overall, high virus titers downplay innate responses, and an increase is seen when viral titers decline. In silico modeling found that TiLV segments 4, 5 and 10 carry nucleolar localization signals. Anti-viral effects of TiLV facilitate production of virus at early stage of infection.