Alterations in schooling, shoaling, and startle response behaviors in mummichog, Fundulus heteroclitus, resulting from exposures to the harmful algal bloom neurotoxins, brevetoxin and saxitoxin

J.D. Salierno¹ and A.S. Kane^1,2

¹Aquatic Pathobiology Laboratory, Department of Veterinary Medicine, University of Maryland, College Park, MD, USA
²Virgina-Maryland Regional College of Veterinary Medicine, College Park, MD, USA

Harmful algal blooms (HABs) in the mid-Atlantic United States, and associated observations of fish morbidity and mortality, have increased in frequency and severity over the past several decades. The ability to predict and characterize environmental effects of different HAB species is essential to HAB remediation and control. This study investigated the exposure effects of relevant, low-level HAB neurotoxins on swimming behavior of twelve groups of 5 mummichog, Fundulus heteroclitus. These neurotoxins included saxitoxin (STX, 100 and 150 µg/L) and brevetoxin (PbTx-2, 40 and 55 µg/L). Thirty-minute video segments before, during, and after neurotoxin exposure were captured using a videography system (Videoscript Professional©, v. 3.1) and were evaluated using software designed for the analysis of interactions, schooling and shoaling behaviors. Predator avoidance (overhead visual bird model) and startle response (auditory/vibratory stimulus) behaviors in groups of mummichog were compared before and after toxin exposure. In an attempt to link behavioral alterations with neuronal signaling in the brain, changes in brain activity resulting from STX and PbTx-2 exposure were quantified using neuronal c-Fos expression. Mummichog groups exposed to both concentrations of STX showed significantly decreased interactions (50%) as well as decreased schooling and shoaling frequencies. Fish exposed to both concentrations of PbTx-2 showed increased interactions (30%) and schooling frequency (25%). Shoal and aggregation size significantly decreased after exposure to both HAB toxins. Additionally, exposure to both toxins significantly altered specific components of startle- and predator response behaviors. The c-Fos neuronal activity assay revealed similar results, whereby STX exposure significantly decreased brain activity while PbTx-2 increased brain activity. These behavioral and neuronal alterations further confirm the known paralytic and excitatory actions of STX and PbTx-2. These results suggest that sub-lethal exposure to HAB toxins can have demonstrable effects on swimming and social behaviors, startle response and predator avoidance behaviors, and brain activity. This is the first study to documents alterations in social behavior of fish exposed to HAB toxins. This data will provide a better understanding how environmentally realistic concentrations of HAB stressors affect fish behavior.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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