Evaluating the toxicity of silver nanoparticles on the behaviour and and physiology of bristlenose catfish (Ancistrus cirrhosis)

Abstract

Silver nanoparticles (AgNPs) are a common material found in many household items, but as these items are thrown out, AgNPs can leach into the aquatic environment, and are currently being found in increasingly higher concentrations in our water supply. In the aquatic environment, AgNPs aggregate and fall to the bottom, affecting benthic creatures. In this study, the Bristlenose Catfish (Ancistrus Cirrhosis) was used for their benthic nature and their ability to air breathe using their highly vascularized stomachs. By analyzing air breathing frequency (seen only in times of stress), we can better understand what role AgNPs play in a catfish’s ability to tolerate environmental stress. Experimentation was done by isolating catfish for seven days with the absence or presence of AgNPs. On the eighth day, these fish were exposed to one of three environmental conditions: control (optimal conditions), hypoxia (20% O2 saturation), and high temperature (32°C). These fish then had their movement tracked and quantified over 6 hours. In addition to this, fish were placed in a respirometer to measure oxygen consumption, gills were analyzed via scanning electron microscopy, and gut samples were used to determine malondialdehyde (MDA) concentration. It was found that fish regardless of environmental stressor or AgNP presence total distance moved did not change. However, hypoxic fish exposed to AgNPs were found to increase air breathing frequency. This indicates that any movement the catfish is doing is focused on air breathing, which could increase their exposure to aerial predators. Respirometry analysis showed an increase in oxygen consumption only when AgNPs are present, which is in keeping with behavioral data, since an increase in basal oxygen consumption would lead to a higher air breathing frequency. MDA levels varied between environmental stressors in AgNP exposed fish, but qualitative gill analysis indicated that the gills were not damaged from nanoparticles. Together, these results support our hypotheses that AgNPs do interfere with a catfish’s ability to tolerate environmental stress. It is expected that with an increase in concentration or exposure times, these effects would increase proportionally.