Combined effects of flow condition and parasitism on shoaling behaviour of female guppies Poecilia reticulata

Abstract

Group living in fish can provide benefits of protection from predators and some parasites, more efficient foraging for food, increased mating opportunities and enhanced energetic benefit when swimming. For riverine species, shoaling behaviour can be influenced by various environmental stressors, yet little is known how flow rate might influence the shoaling of diseased fish shoals. In view of the increasingly unpredictable flow rates in streams and rivers, this study aimed to assess the combined effect of flow condition and parasitism on the shoaling behaviour of a model fish species. Shoal size, shoal cohesion and time spent shoaling of female guppies Poecilia reticulata were compared when infected with the directly transmitted ectoparasite Gyrodactylus turnbulli under flow and static conditions. Flow condition was an important factor in influencing shoaling behaviour of guppies with the fish forming larger shoals in the absence of flow. When a shoal member was infected with G. turnbulli, shoal cohesion was reduced, but the magnitude of this effect was dependent on flow condition. In both flow and static conditions, bigger fish formed larger shoals than smaller counterparts. Future changes to stream hydrology with more frequent flooding and drought events will affect the shoaling tendency of fish. During high-flow events, diseased fish may not be able to keep up with shoal mates and therefore have a higher risk of predation. Additionally, these findings may be important for aquaria and farmed species where an increase in flow rate may reduce aggregation in fish.

Parallel and nonparallel behavioural evolution in response to parasitism and predation in Trinidadian guppies

“…Of particular relevance to our study, Gyrodactylus infection influences, and is influenced by, various aspects of behaviour. For instance, Gyrodactylus ‐infected guppies show impaired swimming ability and reduced activity due to fin damages (López, ; Cable et al ., ), reduced shoaling cohesion (Croft et al ., ; Hockley et al ., ) and lower boldness (Richards, ). In addition, infection risk is influenced by shoaling and other behaviours (e.g.…”

To group or not to group: Effect of prolonged exposure to predation and resource availability on the shoaling behaviour of zebrafish (Danio rerio)

“…Although we expected the two high predation treatments (HP-HF and HP-LF) to have greater shoal compactness than the LP-LF group, we found no significant difference in shoal cohesion. Increased shoal size increases competition for other social factors such as mating (Alexander 1974;Hoogland and Sherman 1976) and also increases the risk of parasitism (Phillips 1924;Freeland 1976;Duffy 1983), which could lead to reduced shoal cohesiveness (Alexander 1974;Mikheev 2009;Hockley et al 2014). Thus, the tendency of fish to stay close to each other due to predation pressure may not be strong enough to overcome the tendency to repel each other within the shoal in order to reduce competition for other social factors (Mikheev 2009;Shelton et al 2015).…”

Assessing the effects of water flow rate on parasite transmission amongst a social host

“…However, shoaling tendencies have been observed to diminish in higher flow rates in common minnow (Garner, 1997), three-spined sticklebacks (Sneddon et al, 2006), and zebrafish (Suriyampola et al, 2017). Contrastingly, Hockley et al (2014) showed that in no-flow conditions, the shoaling tendencies of Trinidadian guppies (Poecilia reticulate Peters, 1859) were significantly reduced compared to those experiencing flowing water, but only following the introduction of Gyrodactylus turnbulli Harris, 1986 infection. This indicated that parasitism may have a greater influence than flow in determining shoaling preferences.…”