Ahmed M. Darwish

Laboratory Efficacy of Florfenicol against Streptococcus iniae Infection in Sunshine Bass

An experimental feeding trial was performed to evaluate the efficacy of florfenicol (FFC) in controlling Streptococcus iniae infection in sunshine bass (female white bass Morone chrysops x male striped bass M. saxatilis). Five dosage levels of FFC in medicated feed were administered daily: 0, 5, 10, 15, and 30 mg of active ingredient/kg of fish body weight. Treatment was started within 22-24 h postchallenge by waterborne exposure to virulent S. iniae. The FFC medication was continued for 10 consecutive days, followed by a 25-d posttreatment observation. At the conclusion of the experiment, FFC treatment significantly increased the survival of S. iniae-challenged sunshine bass from 4.2% in the nonmedicated (positive control) group to 69.2% in the 5-mg/kg dosage group, 86.7% in the 10-mg/kg group, and 94.2% in the 15- and 30-mg/kg groups. Survival was significantly higher in the 15- and 30-mg/kg treatment groups than in the 5-mg/kg treatment group; differences among the 10-mg/kg and higher dosage groups were not significant. Survival curve analysis using a log-rank test indicated no significant difference between curves for the 10- and 15-mg/kg groups but a significant difference between curves for the 5- and 10-mg/kg groups. At the end of the experiment, no carriers were detected in any challenged group receiving an FFC-medicated diet, but the bacterium was recovered from the nonmedicated challenged survivors of the infection. The results of the experiment suggest that the optimum therapeutic daily dose of FFC is between 10 and 15 mg/kg body weight for 10 d.

Chronic exogenous kisspeptin administration accelerates gonadal development in basses of the genus Morone.

The present study assesses the effects of chronic administration of peptides to fish, termed kisspeptins, which are the products of the KISS1 and KISS2 genes, and have been shown to control the development of puberty in animals. Using ecologically and commercially important species (white bass, Morone chrysops, striped bass, Morone saxatilis, and their hybrid) as comparative models, we determined that repeated bi-weekly injections (over 7 weeks) differentially accelerate puberty, as evidenced by increases in the prevalence of spermatozoa in the testes of juvenile fish. Moreover, in sexually mature fish, kisspeptin treatment led to increased gonad weight, gonadosomatic index, and spermatocrit in some white and striped bass. Additionally, mature white bass treated with kisspeptins showed an advancement in oocyte development as determined by histological examination. These gonadal changes occurred in the absence of any photothermal manipulation or hormone injections. To date, this is the first description of kisspeptin-mediated pubertal initiation in fish, and the first evidence that kisspeptins could modulate gonad maturation. Although it remains to be determined how kisspeptins may best be utilized in practice, our findings are a basis for future studies to characterize the molecular underpinnings of the KISS system in various fish species.

Laboratory Efficacy of Amoxicillin for the Control of Streptococcus iniae Infection in Blue Tilapia

Abstract Experimental feeding trials were performed to evaluate the efficacy of amoxicillin (AMX) in controlling Streptococcus iniae infection in blue tilapia Oreochromis aureus. The doses of AMX active ingredient tested were 0, 5, 10, 30, and 80 mg/kg of fish body weight (BW) per day. Administration of medicated feed started within 22–24 h postchallenge by waterborne exposure to S. iniae (after skin scraping) and continued for 12 consecutive days, followed by a 17-d posttreatment observation. Oral administration of AMX-medicated feed for 12 d at a daily rate of 10, 30, and 80 mg/kg BW significantly increased the survival of S. iniae−infected tilapia from 3.8% in the challenged, nonmedicated positive control to 45, 75, and 93.8%, respectively. The survival rate was significantly higher in the 80-mg treatment (93.75%) than the 10-mg treatment (45%) but did not differ significantly between the 10-mg (45%) and 30-mg (75%) treatments. At the conclusion of the experiment, no carriers were detected in any chall...

Histological and Hematological Evaluation of Potassium Permanganate Exposure in Channel Catfish

Abstract A histological and hematological study was performed to evaluate the effect of waterborne exposures of channel catfish Ictalurus punctatus to potassium permanganate (KMnO4). Three concentrations of KMnO4 were chosen to represent one, three, and five times the therapeutic concentrations (0.438, 1.315, and 2.190 mg/L, respectively), based on the KMnO4 demand, for 36 h, which is three times the usual treatment duration. The organs examined were the gill, liver, and trunk kidney. Differential leukocyte counts of neutrophils and monocytes in the blood and plasma enzyme analyses (lactate dehydrogenase and alanine transaminase) were also performed. The gill was the only organ to show microscopic lesions. Fish exposed to the therapeutic concentration of KMnO4 for 36 h had mild hypertrophy and spongiosis in the gills sampled during exposure, but no lesions were noticed 2 d postexposure. Gills of fish exposed to three and five times the therapeutic dose had extensive hyperplasia, epithelial hypertrophy and...

Laboratory Efficacy of Amoxicillin for the Control of Streptococcus iniae Infection in Sunshine Bass

Abstract An experimental trial was performed to evaluate the efficacy of amoxicillin in controlling Streptococcus iniae infection in sunshine bass (a hybrid of female white bass Morone chrysops × male striped bass M. saxatilis). Minimum-inhibitory-concentration studies of amoxicillin against multiple S. iniae isolates showed a sensitivity range of 0.0156–0.5 μg/mL. The amoxicillin dose levels tested were 30, 50, 80, and 120 mg of active ingredient per kilogram of fish body weight per day. Administration of medicated feed started 1 d after infection by immersion exposure to S. iniae and continued for eight consecutive days; this was followed by an observation at 15 d posttreatment. Amoxicillin increased the survival rate from 1% in the infected, nonmedicated group to an average of 95% in the infected groups receiving the four doses; there were no significant differences among the medicated groups. Survivors of the infection were not found to be carriers of the bacteria (i.e., there was negative bacterial i...

Europium-sensitized luminescence determination of oxytetracycline in catfish muscle

An europium-sensitized time-resolved luminescence (TRL) method was developed to determine oxytetracycline (OTC) in cultivated catfish muscle. Extraction of OTC from fish muscle was performed with pH 4.0 ethylenediaminetetraacetic acid (EDTA)-McIlvaine buffer and clean up with hydrophilic-lipophilic balanced copolymer solid phase extraction (SPE) cartridges. The eluate was used without further concentration for TRL measurement in pH 9.0 micellar tris(hydroxylmethyl)aminomethane (TRIS) buffer. Cetyltrimethylammonium chloride (CTACl) was used as surfactant and EDTA as a co-ligand. The excitation and emission wavelengths were set at 388 and 615nm, respectively. The linear dynamic range was 0-1000ngg(-1) (R(2)=0.9995). The recovery was 92-112% in the fortification range of 50-200ngg(-1) and the limits of detection (LOD) ranged from 3 to 7ngg(-1). Incurred catfish samples were used to demonstrate the performance of the method around 100ngg(-1), the European Union maximum residue level.

Evaluation of potassium permanganate against an experimental subacute infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus (Rafinesque)

An experiment was performed to evaluate the efficacy of potassium permanganate (KMnO4) as a prophylactic and therapeutic treatment of an experimental subacute infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus. Fish were cutaneously abraded and divided into five treatment groups: (i) challenged by waterborne exposure to F. columnare and not treated with KMnO4 (positive control), (ii) challenged and simultaneously treated with KMnO4, (iii) challenged and treated with KMnO4 at 1, 6 and 9 days post-challenge, (iv) not challenged and treated with KMnO4 at 1, 6 and 9 days post-challenge (first negative control) and (v) not challenged and not treated (second negative control). The dosing of KMnO4 was 2.0 mg L(-1) above the potassium permanganate demand for 2 h duration. The survival of the group challenged and simultaneously treated with KMnO4 (99%) was significantly higher than the positive control (78%) and was not significantly different from the negative control groups. The challenged fish treated with KMnO4 post-challenge had 7% higher survival than the positive control (85% compared with 78%), but that difference was not statistically significant. The results demonstrate that KMnO4 has a clear prophylactic value but probably a marginal therapeutic value once the infection has established.

Laboratory Efficacy of Oxytetracycline for the Control of Streptococcus iniae Infection in Blue Tilapia

Abstract Experimental trials were performed to evaluate the efficacy of oxytetracycline in controlling Streptococcus iniae infection in blue tilapia Tilapia aurea. Minimum-inhibitory-concentration studies of oxytetracycline against multiple S. iniae isolates indicated a general sensitivity at concentrations of 0.25–0.50 μg/mL. The dose levels tested were 25, 50, 75, and 100 mg active ingredient per kilogram of fish body weight per day. Administration of medicated feed started within 4–5 h after infection by waterborne exposure to S. iniae (after skin scraping) and continued for 14 consecutive days, followed by a posttreatment period of 21 d. The 50-mg treatment significantly increased the survival of infected fish from 7% in the nonmedicated group to 45%. The 75- and 100-mg treatments had survival rates (85% and 98%, respectively) that were significantly higher than that of the 50-mg treatment. There was no significant difference between the 75- and 100-mg treatments and the uninfected, nonmedicated treat...

In Vitro and In Vivo Evaluation of Potassium Permanganate Treatment Efficacy for the Control of Acute Experimental Infection by Flavobacterium columnare in Channel Catfish

Abstract An experiment was performed to evaluate the in vitro and in vivo efficacy of potassium permanganate (KMnO4) against Flavobacterium columnare. In vitro, F. columnare treated with KMnO4 at 2 mg/L for 8 h exhibited a 70% reduction in colony-forming units (CFU). A minimum KMnO4 concentration of 10 mg/L was needed to inhibit bacterial growth. An acute and systemic experimental infection was produced in channel catfish Ictalurus punctatus by waterborne exposure to the bacteria after mechanical cutaneous abrasion to remove mucus and epithelium. At 22 h postchallenge, an 8-h treatment with KMnO4 at 2.3 mg/L (2.0 mg/L above the average KMnO4 demand of 0.3 mg/L) was initiated. This did not reduce mortality in experimentally infected fish. The infection model utilized in the experiment was evaluated by examining the clinical signs and histopathology of infected fish. Fish in the model showed columnaris signs similar to those of a natural infection, including skin depigmentation and ulceration and gill necro...

Improved method for determining antibiotic susceptibility of Flavobacterium columnare isolates by broth microdilution.

A simple and reproducible microdilution method was developed to test the susceptibility of the bacterium Flavobacterium columnare to antibiotics in vitro. The testing was conducted at 28 degrees C for 44-48 h at two dilutions of Mueller-Hinton broth (DMHB) using a standardized inoculum, a reference isolate of Escherichia coli ATCC25922 as a quality control organism, positive and negative control wells, and standardized custom-made microtiter plates. The E. coli ATCC25922 and F. columnare ATCC23463 (the species type strain) had significantly better growth in DMHB at 1:5 (4 g/L) than at 1:7 (3 g/L). The E. coli ATCC25922 was found to be acceptable as a reference isolate and produced minimum inhibitory concentration (MIC) values similar to those in the range published by the Clinical and Laboratory Standards Institute derived using standard Mueller-Hinton broth. The new method was used to determine the MIC of 23 F. columnare isolates (representing the three genotypes of the species) to enrofloxacin, ampicillin, oxytetracycline, erythromycin, florfenicol, flumequine, ormetoprim/sulfadimethoxine, and oxolinic acid.