UTTAR PRADESH JOURNAL OF ZOOLOGY

Background: Chemical communication and olfactory-based sibling recognition are essential for shoaling behaviour, survival, and social organization in fishes. However, aquatic pollutants such as Sodium Lauryl Sulphate may disrupt these chemosensory mechanisms by damaging the olfactory epithelium of Systomus sarana.

Aim: Fish populations are exposed to many different man-made chemicals present in their habitat. These chemicals may interfere with their chemo-sensory ability causing serious damages to various life processes. The present study analyses how pollutants like Sodium Lauryl Sulphate, an anionic surfactant present in detergents, affects the sibling odour recognition ability of Systomus sarana.

Study Design: Fish exposed to sub-lethal concentration of Sodium Lauryl Sulphate for 168h, failed to differentiate the odour cues of siblings and heterospecifics while the control fish exhibited preference to sibling odour cues. Further, examination of the olfactory epithelium using the scanning electron microscopy revealed damaged epithelial cells accounting for the toxic effects of Sodium Lauryl Sulphate on chemosensory organs of the fish.

Place and Duration of Study: Fish were collected from canals associated with paddy fields of Irinjalakuda (10o25’, 10o18’47” N lat. and 76o17’19”, 76o12’48”E long.), Thrissur district, Kerala, India. The fishes were acclimatized with laboratory conditions and induced to breed to form the experimental and stimulus shoals. Methodology: In a dichotomous choice test, both the control and test fish were given an opportunity to swim near the water scented with odour cues of either siblings or heterospecifics without any direct visual contact. The time spent by the fish within the preference zone was recorded for six minutes. Sibling recognition ability of the fish was measured after 72hrs (3 days), 120hrs (5 days) and 168hrs (7 days) of exposure to SLS. Data were normalized using arcsine transformations. Since the correlation between the samples were significant, the data analyzed using parametric dependent sample two-tailed ‘t’ test. The olfactory epithelial tissue of the fish was examined under Scanning Electron Microscope.

Results: Throughout the experiment, the control fish spent significantly more time near the compartment having water scented with the odour of their siblings. The test fish, after 72h of exposure to SLS, successfully discriminated the sibling odour cues and associated with it. However, as the duration of exposure extended it failed to discriminate odourcues of siblings from heterospecifics. The SEM analysis shown damages in epithelial tissues of the test fish.

Conclusion: Shoaling behavior is highly important from a conservation perspective as it enhances the survival and stability of fish populations. Any factor that interferes with the cohesive shoaling of fish may raise concern about its survival. Considering the broad range of toxicological affects of surfactants on aquatic life, special attention should be given to reduce the excessive use.