Behavior and brain size of larval zebrafish exposed to environmentally relevant concentrations of beta-methylamino-l-alanine

Abstract

Harmful algal blooms (HABs) release toxic compounds in water and are increasing in frequency worldwide. The neurotoxin β-methylamino-l-alanine (BMAA) is released by HABs and has garnered much attention over the past 20 years due to its association with human neurodegenerative disorders, but its effects on wildlife are still largely unknown. This study characterized the effects of chronic exposure to environmentally relevant concentrations of BMAA on the behavior and brain size of developing zebrafish (Danio rerio). Zebrafish were continuously exposed to 0, 1, 10, or 100 µg/l waterborne BMAA between 0- and 5-days postfertilization (dpf) before the onset of exogenous feeding. At 5 dpf, locomotion and responses to vibrational and visual stimuli were assessed. Following behavioral testing, larvae body and brain size were measured. Survival between 0 and 5 dpf did not differ between treatments. Moreover, BMAA exposure did not affect thigmotaxis, startle response magnitude, habituation to repeated presentation of vibrational startling stimuli, or relative brain size. A moderate increase in overall activity was observed in larvae exposed to 10 μg/l BMAA under light, but this effect was not seen in dark conditions, indicating that visual processing may have been affected by chronic BMAA exposure. Thus, passive continuous exposure to environmentally relevant concentrations of BMAA prior to first feeding in zebrafish did not affect survival or selected measures used to represent brain development, anxiety, and motor reflexes, but a limited light-dependent effect on locomotion suggests targeted neurotoxicity within the visual system.

Keywords: behavior; brain size; harmful algal blooms; neurotoxicity; zebrafish; β-methylamino-l-alanine.