Creation in biofilters of favorable conditions for the existence of biocenoses secures RAS from the toxic effects of nitrites, which until recently did not attach great importance to toxicants for aquatic organisms. However, it has been found that they are very toxic to fish and aquatic invertebrates. The purpose of the work was to investigate the effect of microbiological starter of the "Filtronorm-D" biofilter filler on the behavior of adult rainbow trout during the launch of the biofilter.
Investigation of the influence of the microbial starter of the filtrotorm-D biofilter filler on the behavior and clinical condition and the preservation of rainbow trout during the launch of the biofilter of the ultrasound has been studied.
Evaluated the clinical signs of adult rainbow trout during the launch of the biofilter CWS for the use of polypropylene filler RK PLAST-control in it. According to the second variant, the clinical signs of adult rainbow trout were evaluated during the startup of the biofilter of the ultrasound scanner for the use of polypropylene filler RK PLAST in it and the addition of the microbiological starter of the biofilter "Filtronorm-D" – experiment. In the experimental group, the biofilter water was introduced by our microbiological starter, biofilter filler "Filtronorm-D", containing live cultures of nitrifying and denitrifying bacteria in the amount of 107 CFU/cm3.
On the 10th day of the experiment, after the application of the microbiological starter of the biofilter filler "Filtronorm-D",
approximately 5 % of the fish with the initial clinical signs of nitrite poisoning were detected. The fish for a long time stood motionless in the corners of the pool, they had the darkening of the body and the brown color of the gills. On the 15th day after the launch of the CWS and the use of "Filtronorm-D", changes in behavior were detected in most of the research objects, which may indicate an increase in the amount of nitrites in water and their effect on the body of trout. Approximately 25 % of fish for a long time stays motionless in the corners of the pool, the mobility of the whole fish has decreased, some individuals have risen to the surface of the water. Changes in pigmentation of the body were also found in approximately
10 % of the individuals. The body became darker, the fins were sealed, the gills got brown color. During this trial period, the mortality rate of the fish was 1,3 %. On the 20th day of the experiment, the signs of nitrite poisoning of fish became increasingly pronounced. Approximately 30 % of the fish showed the presence of darkening of the body and fins, the latter were sealed. In the same fish, the changed color of the gills was observed – from red to brown. In addition, during this period of research, the highest trout death was determined – 3,1 %, which is almost 2.4 times (p <0,05) higher than in the 15-day period. The period of ultrasound starting from the 20th to the 25th day was characterized by a decrease in the content of nitrites from 1,1 mg/dm3 to 0.6 mg/dm3. The process of reducing the content of nitrites in water affected the activity of fish – only about 20 % of trout swam in the upper layers of water. On the 30th day of the launch of the ultrasound with the use of the microbiological starter of the biofilter filler "Filtronorm-D" no signs of nitrite poisoning in rainbow trout were noted. The loss of fish in the indicated period was practically not marked. At the same time, during the application of polypropylene filler RK PLAST without the addition of a microbiological starter of the biofilter filler "Filtronorm D", the most problematic period for fish, in which it is most dying due to the effect of nitrites, is the period from 25 to 30 days.
Thus, the conducted researches prove that during the launch of ultrasound for the use of polypropylene filler RK PLAST in it and the addition of the microbiological starter of the biofilter fillter "Filtertronorm D" the most dangerous is the period from 15 to 20 days. During this period, the largest death of fish and signs of nitrite poisoning is recorded, which requires the implementation of veterinary and sanitary preventive measures to reduce the toxic effects of nitrites.
Key words: RAS, rainbow trout, biofilter, "Filtronorm-D", nitrites, fish behavior, signs of poisoning.
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