Nile Tilapia Oreochromis Niloticus Research Articles

On‐farm growth performance of different strains of tilapia, Oreochromis niloticus reared in earthen ponds

AbstractThe growth of aquaculture sector in Kenya has been anchored on farmed Nile tilapia Oreochromis niloticus. Different strains of the species exist in Kenya with unknown quality due to lack of stock improvement programmes coupled by variations in breeding and management practices in different hatcheries. The seeds supplied to farmers have not exhibited good performance and resilience to changing climate. There is need to validate the quality of strains supplied to fish farmers in Kenya. This study sought to compare the growth performance of three strains of farmed Nile tilapia; Sagana strain (SAG‐F8) produced through selective breeding, super YY strain (KAM‐YY) from Kamuthanga fish farm and the local strain (LOC‐T) obtained from Siaya County. The fish were stocked in fertilised earthen ponds measuring 300 m2 in triplicates at 3 fish/m2. The fish were fed on 35% crude protein diet for 180 days at Bukani Aquapark located in Busia County, Kenya. There was no significant difference in mean weight gain (MWG) between SAG‐F8 and LOC‐T strain exhibiting 159.786 ± 6.76 g and 158.623 ± 4.67 g, respectively. However, under similar conditions, the KAM‐YY strain had a significantly lower MWG (131.74 ± 4.75 g) compared to the two strains. Food conversion ratio (FCR), specific growth rate (SGR) did not demonstrate any significant difference among the different strains. The body protein content in the SAG‐F8 fish strain was higher (65.40 ± 0.20%) followed by LOC‐T strain (61.23 ± 2.34%) and lastly KAM‐YY strain had the lowest (60.37 ± 0.89%). In this study, the impact of genetic improvement has been demonstrated to influence growth and feed efficiency as well as body composition. These improved strains will substantially increase fish production and productivity, hence, a positive impact on the fish farmers' livelihoods when supplied to the farmers and seed multipliers.

The effect of polysaccharide from Padina boergesenii on Aeromonas hydrophila resistance and growth, biochemical, digestive enzymes, non-specific immune response in Oreochromisniloticus

The present study was designed to investigate the sulfated polysaccharide isolated from Padina boergesenii influenced immunological mechanisms and disease resistance in Nile tilapia Oreochromis niloticus after being infected with Aeromonas hydrophila. FTIR, NMR and HPLC were used to characterize the isolated Sulphated polysaccharide extracted from P. boergesenii. The antioxidant properties of the isolated polysaccharide were investigated. The experimental group was divided into five groups (T1-T5) and experimental groups (T2-T5) fed with polysaccharides at concentrations of 0.5%, 1.5%, 2.5%, and 3.5%. The Group T1 serves as a control, and the diet contains no polysaccharides. The 45-day study period involved the examination of O. niloticus haematological, immunological, biochemical, digestive enzymes, antioxidant, and growth traits. Growth, biochemical components, digestive enzymes, haematological, immunological, and antioxidant levels were significantly higher in Experiment T4 (2.5%) compared to the other experimental groups. The experimental groups were infected with A. hydrophila after the feeding trial. Our results predict that the feeding polysaccharide-rich diets may help in growth of the fish and develop their biochemical, digestive enzymes, non-specific immune response, and disease resistance in O. niloticus.

Effects of major immunostimulant (Betamune) on health and production of Nile tilapia Oreochromis Niloticus

Effects of major immunostimulant (Betamune) on health and production of Nile tilapia Oreochromis Niloticus

Water temperature explains part of the variation in basal plasma cortisol level within and between fish species.

Within the thermal tolerance range of fish, metabolism is known to escalate with warming. Rapid thermic changes also trigger a series of physiological responses, including activation of the stress axis, producing cortisol. Fish have adapted to their environment by producing a low level of plasmatic cortisol when unstressed (basal), so that thriving in their natural temperature should not impact their basal cortisol levels. Yet, surprisingly, little is known on how temperature affects cortisol within and between fish species. Here, we conducted a phylogenetic meta-analysis to (1) test whether temperature can explain the differences in basal cortisol between species and (2) evaluate the role of temperature on differences in cortisol levels between individuals of a same species. To do this, we retrieved basal plasma cortisol data from 126 studies, investigating 33 marine and freshwater fish species, and correlated it to water temperature. Intra-species variability in basal plasma cortisol levels was further investigated in two species: the European sea bass Dicentrarchus labrax and the Nile tilapia Oreochromis niloticus. Factors such as life stage, sex and weight were also considered in the analyses. Overall, our phylogenetic analysis revealed a clear positive correlation between basal cortisol level and the temperature at which the fish live. The role of temperature has also been confirmed within D. labrax, while it failed to be significant in O. niloticus. In this paper, the influence of habitat, life stage, sex and weight on basal plasma cortisol levels is also discussed. Since some abiotic parameters were not included in the analysis, our study is a call to encourage scientists to systematically report other key factors such as dissolved oxygen or salinity to fully depict the temperature-cortisol relationship in fishes.

Assessment of Length-Weight Relationship of Nile Tilapia Oreochromis niloticus (Linnaeus 1758) from Qua Iboe River Estuary, Southeastern, Nigeria

The Length-Weight Relationship (LWR) of Oreochromis niloticus from the Qua Iboe River Estuary was studied for 12 months; from April 2021-March 2022. Fish samples were collected from the catches of artisanal fisheries using various mesh sizes of gill and cast nets. The b values in males ranged from 2.25-3.08 with a mean of 2.7333 0.2743 while that of the females varied between 2.41 and 2.930 with a mean value of 2.7075 0.1804). The overall growth coefficient in the LWR (W=aLb) ranged from 2.25-3.08 with a mean value of 2.72±0.04. Both males and females recorded negative allometric growth, and the exponents were significantly less than isometric (p<0.05). Higher b values were recorded in males. There was no significant difference between the b-values of males and females (p> 0.05) during this study with the respective exponential relationships. These data indicated that the length-weight relationships were similar in both sexes during the study period. A higher b-value was recorded in the wet season but there was no significant difference (p> 0.05) between the dry (November-March) and wet season (April-October).This study provides the basic information which could enhance production potential of O. niloticus and its sustainable development, culture and management in Qua Iboe River Estuary,Nigeria.

Temperature-associated virulence, species susceptibility and interspecies transmission of a Lactococcus petauri strain from rainbow trout.

Lactococcus petauri is an important emergent aquaculture pathogen in the USA. To better understand environmental conditions conducive to piscine lactococcosis and the susceptibility of fish species, laboratory-controlled challenges were used as models of infection. Rainbow trout Oncorhynchus mykiss maintained at 13 or 18°C were challenged by intracoelomic (ICe) injection with 101, 103 or 105 colony-forming units per fish (CFU fish-1) and monitored for 21 d. At 13°C, trout experienced mortalities of 7, 7 and 0%, and bacterial persistence of 0, 20 and 0% in survivors, respectively. When exposed to the same bacterial doses, trout maintained at 18°C experienced mortalities of 59, 84 and 91%, and bacterial persistence of 60, 66 and 0% in survivors, confirming a significant role of temperature in the pathogenesis of lactococcosis. Additionally, the susceptibility of rainbow trout, Chinook salmon Oncorhynchus tshawytscha, white sturgeon Acipenser transmontanus, Nile tilapia Oreochromis niloticus, and koi Cyprinus carpio to infection by L. petauri was compared using ICe challenges at 18°C. Trout and salmon experienced 96 and 56% cumulative mortality, respectively, and 17% of surviving salmon remained persistently infected. There were no mortalities in the other fish species, and no culturable bacteria recovered at the end of the challenge. However, when surviving fish were used in further cohabitation trials, naïve trout housed with previously exposed tilapia exhibited 6% mortality, demonstrating that non-salmonids can become sub-clinical carriers of this pathogen. The data obtained provide useful information regarding temperature-associated virulence, fish species susceptibility, and potential carrier transmission of L. petauri that can be used in the development of better management practices to protect against piscine lactococcosis.

Effects of the fresh and dried housefly (Musca domestica) larvae in the diets of Nile tilapia Oreochromis niloticus (Linnaeus, 1758): growth, feed utilization efficiency, body composition and biological indices

A 56-day feeding trial was undertaken to assess the ef-fects of housefly maggots (HM) forms (dried and fresh) as protein sources on growth, feed efficiency, and body indices of Oreo-chromis niloticus finger-lings. A control diet (T0) contained 300 g/kg of fish-meal (without HM). Two practical diets with the same formula were prepared with dried HM (T1) and fresh HM (T2) where 66 % of the fishmeal was replaced. Di-ets were fed to triplicate groups of tilapia (mean ini-tial weight: 10.26 ±0.12 g). There was no difference in survival, condition factor, feed conversion ratio, and protein efficiency ratio. Fish fed diets T0 and T1 had sig-nificantly increased (P < 0.05) mean final weight (50.25 ±1.39 - 52.24 ±1.03 g), specific growth rate (2.84 ±0.03 - 2.88 ±0.03 %/day) and weight gain (389.70 ±7.63 - 402.78 ±8.16 %) compared to T2 diet ones (46.30 ±2.03 g; 2.67 ±0.07 %/day and 356.70 ±7.76 % respective-ly). Viscerosomatic and hepatosomatic index in fish fed T1 and T2 diets were significantly higher than those fed T0. The present findings indicate that the dried form of housefly maggot has given the best results in terms of growth compared to the live form. However, housefly forms did not affect feed efficien-cy parameters.

Genetic Characterization of Nile Tilapia (<i>Oreochromis niloticus</i>) Strains from Senegal for Sustainable Local Aquaculture Production

The optimization of aquaculture production requires the selection of efficient strains. Thus, genetic improvement has become one of the important levers to boost the development of aquaculture. The objective of this study was to carry out genetic characterization of Nile tilapia Oreochromis niloticus, one of the most cultivated fish species in Senegal, in order to select an efficient strain to optimize local fish production. Thus, fish from five different populations (Richard-Toll, ANA, ITACA, Mbodiene and Sauvage) were analyzed, with 15 individuals per population. Genetic diversity and population structure were assessed using molecular genetic analyses by sequence characterized amplified region (SCAR) and microsatellite (SSR) markers. The analyses of the SCARII marker were conducted on four populations (ANA, ITACA, Sauvage and Mbodiene) while microsatellite analyses were conducted on all five populations. The results show high levels of polymorphism of SSR markers, and a high level of observed heterozygosity (Ho), indicating a high within-population genetic variability. These results are in agreement with the AMOVA results, which indicated a high within-population genetic variability (94%). The genetic structure analysis by DAPC indicates that the five populations analyzed are structured into four groups, which are highly heterogeneous because they share common allele individuals. The analysis of the genetic structure by AMOVA showed a low degree of differentiation between the populations (6%), in agreement with the genetic differentiation index (Fst = 0.059). The heterogeneity of studied populations implies a genetic flow over time, which may have existed between the original populations. The overall negative Tajima D values and low genetic differentiation indicate an excess of rare mutations in the populations studied, resulting from a recent population expansion from a limited number of initial breeders isolated in locale hatcheries. Thus, further studies with a much larger panel of markers are required to better differentiate the strains and identify the most efficient ones for sustainable local aquaculture production.

Histopathological Alterations in Nile Tilapia Oreochromis Niloticus (L.) as Influenced by Dietary Antiparasitic Drug Emamectin Benzoate at the Recommended and Higher Doses for an Extended Period

The effects of the dietary antiparasitic drug emamectin benzoate (EB) on the biosafety and kidney, liver and intestine tissue histopathology of Oreochromis niloticus were assessed. Extended EB medication at the recommended dose (50 μg/kg biomass/day) for 21 days reduced survival, feed intake and biomass. A dose-dependent hepatotoxic, nephrotoxic and intestinal toxic effects of EB were noticed. Tubular degeneration, glomerulopathy, inflammation and necrotized renal interstitium in the kidney and glycogen-type vacuolation and cytoplasmic degeneration in the liver were observed. The intestine exhibited loss of absorptive vacuoles, mucinous degeneration, necrotized intestinal villi and absorptive region and inflammation. Lamina propria swelling was noticed in the higher-dosed groups. With the termination of medication, the pathological changes were reduced significantly, indicating the ability of fish to mount adaptive responses to recoup. The extended EB administration for 21 days is unlikely to produce adverse and irrevocable effects on fish at the recommended dose.

Effects of dietary inclusion of Seaweed in regular commercial fish feed on proximate composition, minerals and fatty acid profiling of Nile Tilapia Oreochromis niloticus (Linnaeus, 1758)

Feed formulation is important to improve the quality of feed by adding nutritive ingredients. The use of seaweed in fish feed is not usual in our country though these are cultivated in Cox`s Bazar and Saint Martin`s Island for human consumption. This study investigated the effects of seaweed (Hypnea sp.) as supplementation on the meat quality of Nile tilapia. The current study was continued for 3 months using 30 days old more or less similar-sized 30 tilapia fingerlings/aquarium (total of 10 aquariums). Commercial feed was selected based on its easy availability and is frequently used by farmers in rural areas. Collected seaweed was mixed with the formulated feed at four percentages. Finally, five different treatments were applied to the fishes where – T1 (5% seaweed), T2 (10% seaweed), T3 (15% seaweed), T4 (20% seaweed), and T5 (Commercial feed as control) with twoa sets of replications for each. After 3 months of rearing, fish were harvested for proximate composition, minerals, and lipid extraction as well as for the determination of the quantity of different fatty acids in the sample with a trace amount of heavy metals. Heavy metals were detected in tilapia meat at a trace level which is not harmful for human consumption. The findings have a clear indication that a 10% seaweed mixed diet can be considered the optimum amount as supplementary feed for Nile tilapia to improve their nutrient composition.

A new species of Cichlidogyrus Paperna, 1960 (Platyhelminthes: Monogenea: Dactylogyridae) infecting tilapias in Lake Kariba (Zimbabwe), with a discussion on its phylogenetic position

Monogeneans dominate the external parasite fauna of bony fish. During recent years, examination of more populations and species of Cichlidogyrus Paperna, 1960 has led to the (re)description of several species. Cichlidogyrus halli (Price & Kirk, 1967) Price, 1968, for example, has been redescribed several times in the past and has been proposed to encompass many (pseudo)cryptic species. In Lake Kariba (Zimbabwe), specimens of a species of Cichlidogyrus were found that morphologically resemble C. halli. These specimens were found on the gills of native Oreochromis cf. mortimeri and Coptodon rendalli (Boulenger, 1897), and introduced Nile tilapia Oreochromis niloticus (Linnaeus, 1758). A detailed study of the morphology of these specimens, including morphometrics, and a thorough comparison with specimens of C. halli is presented. Part of the COI gene and 18S-ITS1 fragment were sequenced and analysed to provide insight into the phylogenetic placement of these specimens within the Cichlidogyrus–Scutogyrus monophylum. We found that C. halli and the new specimens sp. nov. are sister clades within the same monophyletic clade, and that clear morphological and morphometric differences are present in the dorsal bar of the haptor (auricles almost twice as long as in C. halli) and the male copulatory organ (wider penis stylet, longer accessory piece with a more elongated and less pronounced terminal triangular cap, narrower heel, as compared with C. halli). Based on these results, the new specimens are described as a new species: C. chloeae sp. nov. The role of introduced Nile tilapia as a potential reservoir for native parasites raises concern for potential spillbacks and stresses the need for further monitoring of monogeneans on native and introduced tilapias. http://zoobank.org/urn:lsid:zoobank.org:pub:DAF7DD13-6A31-4271-970B-A03DEEDD3938

Growth performance of different fish species during dry period in Chitwan, Nepal

In order to assess the growth and yield of different fish species during dry period, an experiment was conducted in the Aquaculture Farm of Agriculture and Forestry University, Rampur, Chitwan from 1 April to 10 July, 2021. The experiment included three treatments: T1 (Carp polyculture), T2 (Common carp Cyprinus carpio monoculture) and T3 (Nile tilapia Oreochromis niloticus monoculture), each with three replications. Silver carp (Hypophthalmichthys molitrix 7%), Bighead carp (Aristichthys nobilis 20%), Grass carp (Ctenopharyngodon idella 13%), Rohu (Labeo rohita 30%), Mrigal (Cirrhinus mrigala 10%) and Common carp (20%) were stocked at densities of 1,400, 4,000, 2,600, 4,000, 6,000 and 2,000 fish/ha, respectively. Stocking density of Common carp and Nile tilapia was 20,000 fish/ha. Fish were fed with sinking pellet (28% crude protein) at the rate of 3% of body weight. Gross and net fish yield was significantly higher in T3 (89.89±0.67 t/ha/yr,16±0.25 t/ha/ yr) than in T2 (4.88±0.38 t/ha/yr, 4.05±0.35 t/ha/yr) due to higher (p<0.05) survival in T3 (72.5±11.3 %) than in T2 (40.6±4.5 %). Gross margin was significantly higher in T3 (1,257,482±186,600 NRs./ha/yr) than in T2 (434,250±124,753 NRs./ha/yr). Based on higher survival, yield and gross margin, Nile tilapia monoculture is suitable for dry season.

Mitotic chromosomal abnormalities and DNA polymorphism in the Nile tilapia (Oreochromis niloticus, Linnaeus, 1758) as a biomarker for water pollution by heavy metals.

Mitotic chromosomal aberrations and DNA polymorphism (RAPD marker) were carried out on the Nile tilapia Oreochromis niloticus collected from five sites in Minia governorate, Egypt to test their applicability as biomonitors for heavy metal contaminants of water. The diploid chromosome number of O. niloticus population was 2 n=44. Different types of chromosomal aberrations were recorded (e.g., deletion, ring, centromeric attenuation, end-to-end association, dicentric chromosome, stickiness chromosomes, endomitosis, fragments and chromatid gap). The chromosomal aberrations varied between O. niloticus population collected from five sites, and the most common type was ring (R) chromosomes. Samples obtained from Bahr Yousef and Irrigation drain exhibited the highest aberration frequency. The frequency of chromosomal aberration was positively correlated with the concentration of heavy metals where their concentration in the surface water of Irrigation drain and Bahr Yousef exceeded the limits defined by WHO as well as the concentration of Pb in muscles. The RAPD marker was also used to identify genetic variation among Nile tilapia samples collected from five different water sources. It created polymorphic and unique bands that can be used as genetic markers to track DNA variations. The dendrogram also revealed that exposure to heavy metal pollution causes gradual accumulation of variance, whereas areas subjected to environmental stress showed higher genetic variation and clustered together.

Biological invasion: evidence from a tropical reservoir (Eleiyele, South West Nigeria

The encroachment of freshwater territories by invasive species is a global issue with its associated co-existence, displacement and facilitation of native species. The blackchin tilapia, Sarotherodon melanotheron is one of the most successful biological invasive species. Data on its apparent ecological consequences on native species are rare in Nigerian inland waters. Based on stomach contents analyses, diets, feeding strategies, and dietary niche breadths of two sympatric invasive S. melanotheron and native Nile tilapia Oreochromis niloticus populations in a tropical domestic water supply were assessed for possible convergence. Both species exhibited generalist feeding strategies subsisting mostly on algae but fish eggs and larvae were conspicuous preys of S. melanotheron. Dietary niche of S. melanotheron was wider than that of O. niloticus. Dietary niche overlap was high and significant between these sympatric species. These findings imply that competitive feeding interactions-including predations on vulnerable early life stages may potentially promote invasion success of S. melanotheron in Eleiyele Reservoir.

Effect of pH on Egg Hatching, Larval Growth Performance, and Enzymatic Activity of the Nile tilapia Oreochromis niloticus

Effect of pH on Egg Hatching, Larval Growth Performance, and Enzymatic Activity of the Nile tilapia Oreochromis niloticus

Thymomodulin enhances vaccination responses against Streptococcus agalactiae in Nile tilapia

Streptococcosis caused by Streptococcus agalactiae is a major economic problem for Nile tilapia Oreochromis niloticus production worldwide. Inactivated vaccines are considered an efficient method for controlling streptococcosis. However, during the vaccination process, stress during fish handling could affect the immune response. Immunomodulators, such as thymomodulin, act on the immune system and can improve vaccination responses. Thus, the aim of this study was to assess the immunomodulatory effect of thymomodulin in O. niloticus vaccinated against S. agalactiae. For this, fish were distributed in a factorial design (2x2x6), corresponding to two levels of thymomodulin supplementation (0.0 and 0.3%), two treatments (sterile phosphate buffered saline and inactivated S. agalactiae vaccine). Initially, fish received thymomodulin supplementation for 30 days. Next, fish were vaccinated by injection intraperitoneal (i.p.) of heat inactivated S. agalactiae vaccine. 15 days after vaccination, all fish were challenged i.p. with S. agalactiae and blood samples were collected at 7, 14, 21 days post infection (DPI). Results revealed that fish supplemented with thymomodulin vaccinated or not developed better protection against S. agalactiae than vaccinated fish without thymomodulin. Furthermore, fish vaccinated and supplemented with thymomodulin presented high levels of antibodies after 14 and 21 DPI, suggesting that thymomodulin can promote the immune response in Nile tilapia.

Effects of Chronic Ammonia Exposure on Growth of Genetically Improved Farmed Tilapia (GIFT) Cultured Under Different Densities

AbstractTilapia are among the most widely cultivated fish species in the world, with a high level of importance for freshwater fish production. An important tilapia variety for the international market is genetically improved farmed tilapia (GIFT; Nile Tilapia Oreochromis niloticus). Multiple studies have been developed to determine the maximum concentrations of ammonia (NH3) recommended for the cultivation of various varieties of tilapia; however, there are no specific data for the cultivation of GIFT. Growth results for GIFT fry exposed to NH3 at 0.50, 0.89, and 1.58 mg/L in 69‐d chronic toxicity tests were evaluated. The experiments were conducted in three recirculation aquaculture systems, one for each concentration of NH3. Stocking densities were 33, 66, and 132 fish/m3. Fish were fed ad libitum three times per day. The only mortalities recorded were for treatments with the highest NH3 concentration (1.58 mg/L), which had a cumulative mortality of 89.5%. There were no significant differences in weight gain for the three stocking densities assessed at an NH3 concentration of 0.50 mg/L. Results indicated that GIFT juveniles can be cultured with stocking densities of up to 132 fish/m3 in environments with ammonia concentrations of up to 0.89 mg/L without compromising fish survival, although the daily weight gain was between 30% and 41% lower than the values reported for optimal culture conditions.

Biological Responses of Nile tilapia Oreochromis niloticus as Influenced by Dietary Florfenicol

Antibiotics are used in the treatment of bacterial diseases in commercial aquaculture. In this study, we the biological responses of Oreochromis niloticus juveniles upon dietary florfenicol (FFC) administration at 15 mg (1×) and 45 mg kg biomass−1 day−1 (3×) for 10 days in terms of feed intake, survival, biomass, hematological, erythro-morphological, serum biochemical, and histopathological aberrations as compared with controls. FFC caused a dose-dependent reduction in feed intake, survival, and biomass, with marked variations in hematology, hematological indices, and erythrocytic cellular and nuclear abnormalities, suggesting its apparent cytotoxic and nucleotoxic effects. The serum biomarkers increased significantly in a dose-dependent manner, except for calcium and chloride, which decreased significantly. The therapeutic dose (1×) group exhibited marked histopathological aberrations, such as renal tubular epithelial degeneration and a widened lumen in the kidney, as well as glycogen-type vacuolation and cytoplasmic degeneration in the liver during the dosing period. The extent of kidney and liver tissue damage was more prominent in the 3× group. The 1× serum biomarker levels became normal, with the exception of alkaline phosphatase, within 3 weeks of suspension of dosing. The recovery of the measured parameters and histopathological and erythro-morphological changes suggested that the therapeutic dietary biological responses induced by FFC are reversible and safe for O. niloticus.

Influence of Substrates on the Quality of Hermetia Meal for Fish Meal Substitution in Nile Tilapia Oreochromis niloticus

Commercially produced black soldier flies (Hermetia illucens) represent a promising fish meal substitute, particularly in the context of using agricultural by-products and waste. Here, the culture of Hermetia maggots on five selected substrates (potato protein (P) as a by-product of starch production, rapeseed oil cake (R) from rape oil production, maize silage (M), soybean (S) meal and, as a control, concentrated chicken feed (C)) were evaluated, assessing the growth performance of Hermetia maggots related to the overall production and the nutritional composition of the respective meal. Subsequently, their use as ingredients in aquafeed formulations was evaluated in a feeding trial with juvenile Nile tilapia Oreochromis niloticus, assessing the growth performance of the fish. Substrates used for Hermetia culture significantly affected the growth and development of the maggots, revealing substantial differences in the meal quality. Still, if incorporated in isonitrogenous and isocaloric diets (33% crude protein, 21–22 MJ/kg) replacing 75% of the fishmeal protein in the formulated diets, no significant differences in growth performance of the fish were observed compared to the fishmeal control. As a conclusion, substrates clearly affect the production yield and the composition of maggots. Nevertheless, this can be compensated by feed formulation as demonstrated by the feeding trial.

Isolation and Characterization of Aeromonas jandaei from Nile Tilapia in Lake Volta, Ghana, and Its Response to Antibiotics and Herbal Extracts.

Production of Nile Tilapia Oreochromis niloticus contributes to economic growth in many countries. However, there has been a decline in its production over the years due to the influx of bacterial infections, with Aeromonas jandaei as an emerging threat. In this study, we identified and characterized A. jandaei from cage-cultured Nile Tilapia in Akosombo Stratum II of Lake Volta in Ghana and evaluated its response to commonly used antibiotics using the disc diffusion and agar well diffusion methods for herbal extracts at various concentrations (10, 30, 50, 70, and 100 mg/mL). The herbs considered included guava Psidium guajava leaf, bitter leaf Vernonia amygdalina, neem Azadirachta indica leaf, and their cocktail (GBNL in the ratio of 1:1:1). The bacterium was isolated from swab samples from the head kidneys of 27 moribund Nile Tilapia collected from nine fish farms. Samples were screened for A. jandaei by culturing and identification using morphological and molecular techniques. The bacterium isolate from fish in the study, identified as A. jandaei GH-AS II, had 92-93% identity to A. jandaei reference strains. Infection of healthy Nile Tilapia (n = 210) with the bacterium isolate showed that 1.0 × 10⁵ CFU/mL was the lethal dose causing 50% mortality. Antibiotic susceptibility testing showed that A. jandaei GH-AS II was resistant to tetracycline and ampicillin. Herbal extracts at the various concentrations inhibited the growth of the bacterium isolate, with a significant increment in the zones of inhibition with increasing concentrations of leaf extracts. However, GBNL showed prominence compared to the other extracts only at 100 mg/mL. Management of A. jandaei GH-AS II by using herbal extracts at Nile Tilapia farms in Lake Volta may be recommended since the use of antibiotics, such as tetracycline and ampicillin, may not yield the needed result.