The aim of this study was to investigate the patterns of antibiotic resistance of Aeromonas spp. bacteria isolated from the sea trout (Salmo trutta) from the state fish hatcheries of the Institute of Food Safety, Animal Health and Environment ‘BIOR’, Latvia. Bacteriological investigations were performed at four state fish hatcheries located in the drainage basins of the main Latvian rivers – Daugava, Venta and Gauja, during the five-year period (2012 – 2016). In fish with visible clinical signs, bacteriological samples were collected from heart, liver, spleen, kidney and ulcer surfaces. Aeromonas hydrophila and Aeromonas salmonicida were isolated from sea trouts. A total of 52 individual sea trouts were examined. Resistance to amoxicillin, ampicillin, cephalexin, colistin, doxycycline, enrofloxacin, erythromycin, florfenicol, gentamycin, kanamycin, lincomycin, neomycin, oxytetracycline, spectinomycin, streptomycin, tetracycline, trimethoprim/sulfamethoxazole was tested. The results of this study suggest a multi-drug resistance pattern among the A. hydrophila isolates. All the isolates were resistant to amoxicillin (100%), ampicillin (100%), cephalexin (100%) and erythromycin (100%). The lowest level of resistance was found against florfenicol (4.55%), gentamycin (4.55%), kanamycin (4.55%), but susceptibility was recorded to enrofloxacin, neomycin and trimethoprim/sulfamethoxazole. A. salmonicida isolates were resistant to oxytetracycline (9.38%) and tetracycline (9.38%). For other antibiotics A. salmonicida isolates were susceptible.

This study was designed with the aim to determine the impact of residual antibiotics on haematological and biochemical constituents of broiler chickens’ blood. For this, one-day-old chickens were randomly divided into four equal groups with 10 individuals in each group (n = 40). All groups of chickens fed with commercial basal diet; the first group considered as control, fed only with basal ration; the feed of the second, third and fourth groups of chicken were supplemented with amoxystin, tetracycline and chloramphenicol, respectively. Antibiotics were given daily, individually, in sub-therapeutic concentrations: amoxystin at the dosage 10 mg kgE-1, tetracycline and chloramphenicol – 20 mg kgE-1 of the chicken’s weight for 41 days. The blood parameters were measured at the end of experiment on the 42nd day. In comparison with the control group, decreasing of leukocytes was observed in the 2nd and 4th groups, and increasing in the 3rd group of broilers. The concentration of erythrocytes and hemoglobin was reduced in the 2nd group and hematocrit was higher in the 3rd and 4th groups (p is less than or equal 0.01). The total protein was decreased by 22% in the 2nd group, 16% – in the 3rd and 4th groups as compared to the control group (p is less than or equal 0.01) in blood serum. The concentration of glucose was decreased by 45.8, 46.5 and 51.5% in the second, third and fourth groups of treated birds, respectively, compared to those of birds in the control group (p is less than or equal 0.01). Based on the results it could be concluded that antibiotics influence the dynamics of haematopoiesis and biochemical indices of broilers.