Effectiveness of oxytetracycline in reducing the bacterial load in rohu fish(Labeo rohita,Hamilton)under laboratory culture condition

Objective:To observe the effectiveness of most widely used antibiotic,oxytetracycline(OTC)in reducing the bacterial load in rohu fish under artificial culture condition in the laboratory.Methods:The experiment was conducted in the Faculty Fisheries,Bangladesh Agricultural University,Mymensingh-2202.The fish were reared in 8 aquaria where fish in 5 aquaria were used for replication of the treatment(experimental group)and fish in remaining 3 aquaria were considered as a control(Control group).OTC was fed to the fish in the experimental aquarium at the rate of 2 g/kg through diet twice daily whereas fish reared under control condition was given feed without antibiotic for 20 d and bacterial content in the aquarium water,gills,skin and intestine of fish were estimated at every alternative day after onset of the experiment.Results:Rearing the fish with OTC treated feed resulted in gradual decrease of bacterial load in the aquarium water,gills,intestine and skin of the fish whereas the content remain unchanged Or little increased in the control group.W ater quality parameters such as dissolved oxygen,pH and total hardness were within the suitable range in the experimental aquarium but not in control aquaria throughout the experimental period.Conclusions:These results suggest that OTC could be a potential antibiotic to reduce the bacterial load in fish and can be used commercially for maintaining the fish health in aquarium conditions.

Effects of antibiotic on the bacterial microflora in two commercially important catfish species,Clarias batrachus and Heteropneustes fossilis in Bangladesh

Objective:To assess the effects of a widely used antibiotic,oxytetracycline(OTC)on the bacterial microflora in two catfish species under artificial culture conditions in the laboratory.Methods:The experiment was conducted in the Faculty of Fisheries,Bangladesh Agricultural University,Mymensingh-2202.The fish were reared in six aquaria(size 37 cm×30 cm×60 cm)where three aquaria served as replicates of the antibiotic treatment groups and the remaining three aquaria served as an untreated control group.Each aquarium was stocked with 25 fish on an average body weight 15 g.OTC was administered to the fish in the treatment groups at the rate of 2 g/kg in-feed twice daily upto ad libitum,whereas fish in the untreated control groups were given the same feed without antibiotics for 20 d.During the experiment,bacterial loads were estimated as colony forming unit(CFU/g)by every alternate day in the aquarium water,gills,skin and intestine of fish.Results:The administration of OTC in feed resulted in gradual decrease of bacterial loads in the gills,intestine and skin of the two catfish species tested.In contrast,the bacterial loads remain unchanged or slightly increased in the control groups not fed with OTC.Water quality parameters such as dissolved oxygen,pH and total hardness were found to be within suitable range in the test aquaria but not in control aquarium throughout the experimental period.Conclusions:The results of this experiment showed that in-feed antibiotic OTC for a period of 20d reduced the bacterial loads in the gills,intestines and skin of treated fish.