RESPIRATORY STRESS OF SALINITY ON Oreochromis niloticus

Oreochromis niloticus (Nile tilapia) commonly found in the freshwater bodies of Kerala was used in this study as the experimental fish so as to determine the effect of salinity on the respiration rate of the fish. The fishes were exposed to different salinities (5ppt, 10ppt, 15ppt, 20ppt) for a period of one hour. The sample with 0ppt salinity was taken as the control. Using Winkler’s method, the dissolved oxygen level in the water taken at different intervals (5th minutes, 15th minutes, 30th minutes and 1 hour) from the sample solutions were estimated. In control (0ppt) average oxygen consumption during different time interval was found to be stable at 0.12 mg/ml/g body weight. The dissolved oxygen consumption by fish increased with increasing salinities from 0ppt to 10ppt, then decreased in 15ppt and 20ppt, besides this consumption of Oxygen decreased from 5th minutes to 60th minutes of exposure. The opercular beats of the fish was noted and it was found that in the control (with 0 ppt salinity), the rate of opercular beats was quite steady without a huge rise or fall and the average value noted was 122/minutes. In all other salinities (5, 10, 15 and 20 ppt), the opercular beats was decreased from 1st minute to 60th minute. The rate of opercular beats was lower in the control when compared with 5ppt,10ppt, 15ppt and 20ppt.Even though Oreochromis niloticus (Nile tilapia) is very sturdy fish, and tides over stressful environment conditions, salinity changes in this experimental setup caused changes in the respiration rate of the fish. So this study discloses how other less sturdy aquatic fauna could easily succumb to salinity change in their environment.