Heterogeneous movement by a small non-migratory stream fish

Movement is a basic feature of fish ecology, being related to dispersal, recolonization, and recovery of local populations after disturbance. Non-migratory species are the main component of stream fish communities, especially in the Neotropics, but there is little information on the characteristics of their movement. In this capture-recapture study, we describe the individual movement of the armored catfish Rineloricaria aequalicuspis in a stream in southern Brazil. We also assess whether this species displays heterogeneous movement, as well as its degree of mobility and the relationship between individual fish movement and body size and local habitat characteristics. Data on individual fish positions were obtained monthly from November 2018 to March 2019, in ten 20-m stream sections along a 430-m stream stretch. Individual fish were captured by kick sampling and measured, photographed (for later photo-identification), and released back to the stream. The movement frequency distribution was moderately leptokurtic (kurtosis = 3.31), indicating heterogeneous movement with two groups of individuals, stationary and mobile. The maximum movement distances were 248 m and 208 m, downstream and upstream, respectively, while the mean movement distance was 98.6 m. Density of individuals was the main factor affecting the probability of movement, suggesting a role for resource availability and intraspecific interactions. The heterogeneous movement pattern observed for R. aequalicuspis indicates that intra-populational variability in movement behavior occurs in non-migratory stream species, which have been often assumed to be either sedentary or mobile species. We highlight that sedentary behavior should not be assumed a priori for stream fishes, not even for those species usually considered to be of low mobility, as many loricariids.

Automated summary

The study described individual movement of the armored catfish Rineloricaria aequalicuspis in a stream in southern Brazil, revealing heterogeneous movement and maximum distances of 248 m downstream and 208 m upstream. Density of individuals was found to be the main factor affecting the probability of movement, indicating intra-populational variability in movement behavior.