Zebrafish Case Study

About half of the fish species live in groups at some point in their life

cycle (Pitcher, 1998; Shaw, 1978). Fish living in social groups can gain

significant foraging and anti-predator advantages, but living in a group

also carries a cost, so fish constantly perform a risk-balancing trade-off

and decide to stay, leave or join with other fish effect (for a review, see

Krause & Ruxton, 2002; and Pitcher & Parrish, 1993). The advantages of

living in a group include the dilution effect, that is, a decrease in the

individual risk of being taken by predator in a larger group (Foster &

Treherne, 1981); the confusion effect, that is, the perceptual or cognitive

overloading that predators experience when confronted with a large group

Liu & Leach, 2011; Morris, 2009;

Stewart, Nguyen, Wong, Poudei, & Kalueff, 2014) and drug-induced behavior

(e.g. Gerlai, Ahmad, & Prajapati, 2008), among other topics. Several

authors have studied the collective motion of zebrafish under laboratory

conditions (Miller & Gerlai, 2007, 2008, 2012a; Shelton, Price, Ocasio, &

Martins, 2015) and have observed that it is a social specie which tends to

form tight groups, but also that zebrafish could form both shoals and

schools, depending on the level of stress/habituation, the presence of food

or the presence of a predator. . However, it should be noted that we know

little about the natural history and behavior of zebrafish, but some field

observations suggest that they form small shoals about 2-10 individuals

(Pritchard, Lawrence, Butlin, & Krause, 2001).

Hyphessobrycon is one of the largest genera within the family of

Characidae, and comprises about 130 species distributed from southern

Mexico to the Río de la Plata in Argentina (Carvalho & Langeani, 2013;

Dagosta, Marinho, & Camelier, 2014; García-Alzate, Valencia, &

Moreover, several studies

suggest that the genus is polyphyletic (e.g., Javonillo, Malabarba,

Weitzman, & Burns, 2010; Mirande, 2009, Oliveira et al., 2011), which

compromise the generalization of studies coming from other tetra species to

the black neon tetra. So far, we are not aware of any paper characterizing

the collective motion of this specie neither under laboratory conditions

nor field studies. Nonetheless, the observations of cardinal tetras

(Paracheirodon axelrodi) in the wild, a sister clade to black neon tetras

according to Mirande (2009), note that they swim in groups of few dozens of

individuals (Walker, 2004) but they fail to provide more precise

information.

The study of collective motion is normally based on the multitracking of

videos about groups of fish which are recorded under laboratory conditions,

but there is a great diversity in the experimental setup used by the

researchers. One of these differences is the water column height, some

authors use a shallow water level to restrict the mobility of the fish and

prevent as much as possible the occlusions between the individuals (e.g., 5

cm, Leem et al, 2012; Salierno, Gipson, & Kane, 2008), while others