Locomotor Repertoire of The Larval Zebrafish: Swimming, Turning and Prey Capture

Abstract

Larval zebrafish (Brachydanio rerio) are a popular model system because of their genetic attributes, transparency and relative simplicity. They have approximately 200 neurons that project from the brainstem into the spinal cord. Many of these neurons can be individually identified and laser-ablated in intact larvae. This should facilitate cellular-level characterization of the descending control of larval behavior patterns. Towards this end, we attempt to describe the range of locomotor behavior patterns exhibited by zebrafish larvae. Using high-speed digital imaging, a variety of swimming and turning behaviors were analyzed in 6- to 9-day-old larval fish. Swimming episodes appeared to fall into two categories, with the point of maximal bending of the larva's body occurring either near the mid-body (burst swims) or closer to the tail (slow swims). Burst swims also involved larger-amplitude bending, faster speeds and greater yaw than slow swims. Turning behaviors clearly fell into two distinct categories: fast, large-angle escape turns characteristic of escape responses, and much slower routine turns lacking the large counterbend that often accompanies escape turns. Prey-capture behaviors were also recorded. They were made up of simpler locomotor components that appeared to be similar to routine turns and slow swims. The different behaviors observed were analyzed with regard to possible underlying neural control systems. Our analysis suggests the existence of discrete sets of controlling neurons and helps to explain the need for the roughly 200 spinal-projecting nerve cells in the brainstem of the larval zebrafish.

Neural circuitry for stimulus selection in the zebrafish visual system

“…C-starts were characterized by a large maximum tail amplitude and large bout integral (Burgess and Granato, 2007;Figure 4D, blue cluster). Burst swims exhibited a high tail beat frequency and were symmetric across the midline (Budick and O'Malley, 2000;Figure 4D, red cluster). Slow swims exhibited relatively small values across all three parameters (Figure 4D, green cluster).…”

Neuromodulation and Behavioral Flexibility in Larval Zebrafish: From Neurotransmitters to Circuits

“…When a zebrafish larva encounters a potentially edible object, it needs to switch its behavior from exploration, when it travels relatively large distances, to prey hunting in its immediate surroundings. Larvae hunt preys (in laboratory settings most often unicellular organisms such as paramecia, or small moving visual stimuli simulating them) with a well-coordinated series of fin, tail, eye, and jaw movements performed in sequential steps of prey detection, approach, and ingestion (Budick and O'Malley, 2000;Bianco et al, 2011;Preuss et al, 2014;Semmelhack et al, 2014;Antinucci et al, 2019;Mearns et al, 2020). By using a microscope capable of performing whole-brain calcium imaging at cellular resolution in freely swimming zebrafish larvae (Kim D. H. et al, 2017), Marques et al identified neuronal correlates of exploration and hunting behavior (Marques et al, 2020).…”

“…Moreover, methods for imaging and analyzing activity of a large number of neurons are lowering the barrier for discovering new neuromodulatory circuits (Ahrens et al, 2012;Freeman et al, 2014;Keller and Ahrens, 2015;Randlett et al, 2015;Lovett-Barron et al, 2017;Mu et al, 2020). Finally, zebrafish larvae perform several well-characterized behaviors (Budick and O'Malley, 2000;Orger and de Polavieja, 2017), some of which, such as hunting and threat avoidance, are modulated by internal states (De Marco et al, 2014Filosa et al, 2016;Lovett-Barron et al, 2017). The behavioral repertoire of older zebrafish is wider, including for example territoriality, social, and reproductive behavior (Orger and de Polavieja, 2017), but their larger and opticallyopaque brains constitute an obstacle for optical interrogation of neuronal circuits involved in neuromodulation.…”

Larval Zebrafish Exhibit Collective Circulation in Confined Spaces

“…However, at the 5 days post-fertilization larval life stage, when zebrafish are approximately 4 mm in length, before the onset of social shoaling behavior [25,26], they utilize different movement patterns from adult fish. Larval zebrafish, a millimeter with 2 Ls swimmer move in what is often termed a beat-and-glide or burstand-coast discontinuous manner; they swim in bouts of movement followed by pauses [27]. This species has been extensively studied in terms of their kinematics, neurobiology, development, and behavior [28][29][30][31][32] but the individual or collective motion of larvae in confinement has not been explored previously.…”