Behavioral Effects of Nitrite on Goldfish (Carassius auratus)

Abstract

As the human population grows the demand for food products grows, increasing the need for high agricultural output. This increase in agriculture leads to the frequent use of inorganic fertilizers which can pollute freshwater systems with nitrogenous compounds. Nitrite, a byproduct of fertilizer pollution, can accumulate and reach concentrations between 0.5 μM and 1.0 mM in aquatic ecosystems. Nitrite is known to disrupt physiological processes such as ion homeostasis, respiration, and neural and cardiovascular function. Nitrite is also known to cause methemoglobinemia, the irreversible oxidation of red blood cells. The effect of nitrite on internal organs and functions is extensively studied. However, little is known about the effects of nitrites on external sensitive organs in aquatic animals, where the pollutant is in continuous contact with surface epithelia. The olfactory system is critical for coordination reproductive events, predator avoidance, and food detection in fish. To detect odors, the olfactory system must be continuously exposed to the environment, therefore it is sensitive to pollutants. There is a need to determine the effects of nitrite on the olfactory system in fish. Behavioral trials, using Goldfish (Carassius auratus), were conducted to establish the effects of nitrite on food detection via olfactory system. In order to conduct the behavior trials a two‐choice maze was built. The two‐choice maze had a food odor released in one channel while a control odor was released in the second channel. Each behavior trial lasted twenty minutes and consisted of an acclimation period, pre‐cue exploratory period, re‐acclimation, and a cue exposure period. Time spent in each channel during the pre‐cue exploratory period was recorded to establish preference bias. Time spent in each channel during the cue exposure period was also recorded. To study the effects of nitrite on goldfish feeding behavior, fish were exposed to four different sublethal nitrite concentrations (0 mM, 0.01mM, 0.3 mM, and 1.0 mM), for a week before the behavior trials began. Weekly behavior trials were then conducted for four weeks. A Wilcox rank test was used to determine the preference for food odor, after four weeks of nitrite exposure. The goldfish exposed to nitrite were significantly less attracted to food odor than the control group (p < .05). Food preference decreased as nitrite concentration increased. The results indicate that nitrite negatively affects the olfactory system and it’s ability to detect food odor, therefore showing that sublethal concentrations of nitrite negatively affects food detection before any other physiological function is affected.